A Must-Read for Beginners! What Is Approximate Design? A Thorough, Easy-to-Understand Guide to the Basics

Are you familiar with the term “approximate design” often heard in the fields of construction and civil engineering? This refers to the work of performing a rough design for a planned project and estimating the necessary construction content and costs approximately. It may feel a bit difficult for beginners, but approximate design is a very important step for grasping the overall picture of a project and its budget.

In this article, we explain in an easy-to-understand way the purpose of approximate design, the timing for carrying it out, the information you should prepare, and the actual procedure. We also cover points to watch out for when conducting approximate design and look at concrete examples such as land development, road planning, and disaster recovery, explaining the relationship with on-site surveying and quantity verification. Finally, we introduce LRTK’s simple surveying feature as a tool that can help improve the accuracy of approximate design. Let’s go through the basic knowledge of approximate design together.

What is approximate design?

Approximate design is a simple design task performed in the early stages of a project. Before detailed drawings and specifications are finalized, it defines the plan’s outline (basic policy and layout) and identifies the necessary rough quantities and construction tasks. In short, it is the work of doing a “rough design” to gather information that will serve as the basis for cost estimation.

For example, consider creating a new road. In approximate design you draw an approximate route on a map or existing plan drawing, and tentatively decide the road’s length and width. Then you roughly estimate how much earth needs to be filled or excavated (a earthwork calculation), and what structures (bridges, retaining walls, etc.) might be required. For building construction, you might assume the building area, number of rooms, and main structure type (e.g., reinforced concrete or steel frame), and from the overall volume extract rough quantities.

In approximate design, precision like that of detailed design is not required, but you put together an outline plan necessary to judge the project’s budget and feasibility. In other words, it provides the material for stakeholders to reach a common understanding of “this plan will likely be about this scale and cost.”

Purpose of approximate design

The main purposes of performing approximate design are as follows.

• Understanding the budget: It is done to grasp the money required for a project at an early stage and to formulate a financing plan. The cost estimate obtained from approximate design lets you judge whether the plan is likely to fit within the budget or will be greatly exceeded.

• Checking plan feasibility: It plays a role in confirming the scale and feasibility of the plan in the early stages. If the approximate calculation shows that the required construction volume or cost is far larger than expected, it may be necessary to revise the plan (scale down or consider alternatives).

• Building consensus among stakeholders: It provides the basis for stakeholders—clients, engineers, superiors, or other departments—to share a common understanding of the project’s direction and rough scale. Meetings based on the results of approximate design serve as evidence when agreeing on project policy.

• Schedule and resource planning: Since approximate design reveals the rough volume of work, it helps in planning personnel and construction periods roughly. For example, you can estimate “If this much earth must be moved, this much time and this many machines will be required.”

In short, approximate design aims to provide decision-making material before pushing the project full-scale. By drawing the outline early, you avoid unnecessary investment and proceed efficiently.

When to carry out approximate design

So when should approximate design be performed? Generally, it is carried out at the following timings.

• Initial project planning stage: When the idea for a plan emerges, approximate design is performed to examine whether it can be realized. For example, when a municipality is considering new roads or facilities, cost estimation through approximate design is required before budget requests (preliminary budget requests).

• Budget preparation: It is carried out to estimate required expenses before annual budgeting or funding procurement. Clients often use the results of approximate design to explain the project budget to upper management or finance departments.

• Comparing multiple plans: When there are multiple plan options (for example, two route proposals A and B for a road), each option may be roughly designed to compare costs and volumes. Approximate design provides the basis for judging “which option is more economical” or “which option will likely have a shorter construction period.”

• When plans change: If major changes occur during the planning process, new approximate design is performed to assess the impact. For example, if an unplanned structure becomes necessary as design progresses, you estimate the additional cost approximately to check its effect on the overall project.

• Emergency response: In cases like disaster recovery where an outline construction plan must be prepared quickly, simple design—i.e., approximate design—is performed immediately. Without waiting for detailed surveys, you quickly estimate rough damage quantities and reconstruction work volumes to promptly calculate approximate quantities and costs and enable emergency budget measures.

Thus, approximate design can be called “a design for looking ahead.” It is used in the early and milestone stages of a project to decide or adjust the plan’s direction.

Information needed for approximate design

To perform approximate design, you need to gather several basic pieces of information. Specifically, the following are required.

• Local topography and survey data: Topographic information of the site or area under planning is indispensable. For land development or road works, survey drawings (contour maps or existing condition drawings) that show site elevations and terrain undulations are necessary. Without these, you cannot make accurate earthwork calculations (estimates of how much fill or excavation is needed).

• Field survey results: Actual on-site investigation is important in addition to drawings and numerical information. Walking the site to check ground conditions (presence of soft ground or bedrock), surrounding environment (adjacent buildings, roads, rivers), and construction constraints (narrow roads preventing large machinery access) enables more realistic approximate design.

• Required planning conditions: Information about the specifications and scale the project should achieve. For roads, this might be “what is the width in m” or “what is the design speed in km/h,” and for land development “how many lots to create” or “average lot area in m².” For buildings, “total floor area,” “number of floors,” and “use” are typical. If these conditions are not clear, design cannot proceed, so fix them through hearings with the client or stakeholders.

• Data from past similar projects: In approximate design you need to estimate quantities and unit prices roughly even without detailed drawings. Data from similar past projects is useful. For example, “a previous road project of the same scale had earthwork costs of about ○○ yen per km” can serve as a reference. In public works, it is common to refer to standard unit prices or productivity tables from cost manuals or unit price books.

• Design standards and legal checkpoints: Even in an approximate estimate, you must observe applicable standards. For roads, this includes maximum grade and minimum curve radius; for land development, standards under land development regulations; height restrictions; and structural standards for retaining walls. Check these to confirm whether “this plan is feasible.” If you ignore standards at the approximate stage, detailed design may later require a “redo” of the plan.

Based on the above information, you draw a plan drawing (layout) at the desk and consider a simple section model while proceeding with approximate design. Mix in simple calculations and sketches as needed to build the project outline.

Procedure for approximate design

Approximate design typically proceeds with the following steps.

• Organize planning conditions: First, clarify the project’s purpose and requirements. Organize client-provided requirements and self-set objectives to define “what and how much to build.” For example: “construct a road of ○ m in length,” “develop ○○ m² of land,” or “build a ○-story building.”

• Collect site information: Next, gather information about the site. Confirm survey maps, geological information, locations of existing facilities, presence of buried utilities like water and gas, and land ownership status. If possible, inspect the site, take photos, and interview stakeholders to capture points not apparent from desk data.

• Plan drafting (layout planning): Based on collected conditions, design the layout. Sketch on paper or draw basic diagrams in CAD to specify placement, routes, and shapes. For roads, draw lines on a map to approximate curves and grades; for land development, draw where to cut and fill; for buildings, consider basic floor plans and layouts. At this stage you may sketch multiple options for comparison.

• Quantity takeoff: Once the plan is established, calculate the necessary rough quantities. Extract approximate quantities for main work items. For roads, for example: “earthwork (excavation ○ m³, fill ○ m³)”, “subgrade/pavement area ○ m²”, “bridge length ○ m”, “drainage structures ○ locations.” For land development: “cut/fill volumes ○ m³”, “retaining wall length ○ m”, “development area ○ m².” For buildings: “total floor area ○ m²” and major structural material amounts (concrete ○ m³, rebar ○ t). Accuracy can be rough, but ensure no major omissions of key items.

• Approximate cost estimation: Multiply the quantities by standard or estimated unit prices to estimate costs. Public works often use unit prices based on cost manuals; private projects may obtain rough estimates from specialist contractors. The important point at this stage is to see whether the estimate fits within the budget. If the estimate greatly exceeds the budget, adjust the plan.

• Summarize results: Finally, compile the approximate design results into materials. Organize the layout and main section drawings, quantity tables, and breakdown of approximate construction costs so you can explain them to the client or superiors. Excessive detail is unnecessary, but include assumptions and specifications used. For example, note “this estimate is based on ○○ standards” or “assumed good ground requiring no pile foundations” so decision bases are clear when reviewing later.

These are the general steps for approximate design. In practice, these steps may be divided among a team or higher- and lower-level designs (e.g., overall road approximate design and individual structure approximate designs) may be executed in parallel.

Points to watch in approximate design

When proceeding with approximate design, pay attention to the following points.

• Balance between accuracy and efficiency: Approximate design is just an “outline,” so you do not need to calculate to minute detail. However, an overly rough plan lacks reliability. Within limited time, firmly grasp important points (e.g., earthwork volumes and presence of major structures) and rely on assumptions for minor details—this balance is essential.

• Consideration for uncertainties: In the early stages, information is often incomplete. Allow some margin for uncertain factors such as detailed ground conditions, underground utilities, or future price fluctuations. For example, “add 10% to the earthwork calculation result” or “include contingency in estimates.” Hedging against risk so that later changes do not cause major issues is important.

• Be careful about fixing planning conditions: Once approximate design results are available, they may be perceived as definitive. But approximate-stage plans are provisional. Share with stakeholders that changes and adjustments are likely during detailed design. Keeping flexibility—e.g., “approximate design suggests plan A, but if detailed design is not feasible, plan B is possible”—is a safe approach.

• Frequent communication with stakeholders: Approximate design is often done quickly, so do not proceed unilaterally; communicate with stakeholders regularly. Hearing from site personnel or experienced engineers may reveal overlooked cost factors (provisional works, seasonal construction issues). Beginners especially should consult others to improve the accuracy of their approximate design.

• Use up-to-date information and technology: Relying solely on old data or outdated experience can produce obsolete plans. Consider current material prices and new construction methods. For example, drone surveying and 3D modeling now allow faster and more detailed site understanding, improving approximate design accuracy.

By keeping these points in mind, you can prevent major mistakes at the approximate design stage and make detailed design and construction proceed smoothly.

Example of approximate design for land development

Let’s consider a concrete example: land development (residential land development). Suppose you plan to cut and fill a sloped site to make flat residential lots.

In this case, approximate design examines the following. First, understand the current topography of the development site and decide how high to level the land (development elevation). If you plan to cut high areas and fill low areas to balance the earthworks, calculate the quantities of cut and fill and check whether they balance (earthwork calculation). If surplus excavated soil remains, disposal costs for off-site removal by dump trucks will occur; if soil is insufficient, you need a budget to bring in fill from elsewhere. In approximate design, set broad policies such as “try to balance earthwork on site” or “any unavoidable surplus of ○○ m³ will be disposed off-site.”

Retaining walls and drainage facilities around the development are also necessary. Estimate how many meters of retaining wall of height ○ m are needed, and roughly how much side ditch and catch basin installation is required, then calculate those quantities. Also confirm whether roads to the developed lots, parks, and balancing ponds are needed. For all these elements, determine approximate sizes, quantity takeoffs, and then estimate total construction cost.

For example, consider an approximate design for developing a 10,000 m² hillside. From contour maps you estimate average cut/fill of about 2-3 m (6.6-9.8 ft). The earthwork would roughly be on the order of 20,000 cubic meters. Using the average-section method yields more precise results, but at the approximate stage a rule-of-thumb calculation based on experience is acceptable. Then list major items such as retaining walls totaling 100 m (328.1 ft), internal roads with a width of 6 m (19.7 ft) and a length of 200 m (656.2 ft), water and sewer pipes extending 200 m (656.2 ft), and one neighborhood park. Multiply each item by a rough unit price to conclude that land development will cost roughly “several hundred million yen.”

As shown here, earthwork calculation is the key in approximate design for land development. Because the project significantly alters existing terrain, capturing accurate original topographic information is crucial. In some cases, performing a simple survey at the approximate design stage to obtain more reliable terrain data is warranted.

Example of approximate design for road planning

Next, consider approximate design for road planning. Imagine planning a new road several kilometers long through mountainous terrain.

In road approximate design, first select a route on a map. If multiple candidate routes exist, draw approximate alignments considering curvature and grade. Once a route is chosen, examine longitudinal elevation differences. Calculate grades from start and end elevations and determine whether tunnels or bridges are needed if there are mountain passes or valleys.

For example, you might compare that “this route requires one 50 m (164.0 ft) long bridge because of a deep valley,” while “another route avoids the bridge but increases the distance by 1 km (3280.8 ft).” For each option, estimate earthworks (cut and fill volumes), required structures (number and length of bridges or tunnels), and road area (width × length) to roughly estimate cost and schedule.

As a concrete example, suppose you plan a 5 km (16404.2 ft) local road. From topographic maps you estimate several major cut sections amounting to about 300,000 cubic meters of cut and 200,000 cubic meters of fill. You may determine that 100,000 cubic meters of surplus material will require off-site disposal. There are two bridges of lengths 30 m (98.4 ft) and 100 m (328.1 ft) respectively (the 100 m bridge spanning a large valley will need several piers), no tunnels, and about five major box culverts for transverse drainage. From these quantities you aggregate the road main works cost + bridge works cost + ancillary work cost to conclude the project will cost roughly “○○ hundred million yen” on a preliminary basis.

A key point in road approximate design is that the selected route greatly affects construction cost. It is important to compare multiple options when possible and identify the most efficient plan. In mountainous roads, insufficient surveying or geological investigation can lead to misjudgments, so even at the approximate stage it is advisable to perform on-site checks at critical locations and base plans on the most reliable information possible.

Example of approximate design for disaster recovery

Finally, consider approximate design in the context of disaster recovery—for example, a slope collapse beside a road caused by heavy rain. Rapid reconstruction is needed after damage, but you first perform an approximate restoration design to determine the scale and cost of the work.

On site, quick surveys or drone imaging are usually conducted to rapidly grasp the volume of collapse and the damage extent. Based on that data, estimate “how many cubic meters of collapsed soil” and “how long and how high the collapsed slope is.” For instance, if you determine “about 500 cubic meters of soil have collapsed and blocked the road,” the volume of removal work is clear.

Next, set a restoration policy. Decide whether to simply regrade the slope or to install retaining walls or slope protection to prevent recurrence. In approximate design, consider a minimum structure that ensures safety. For example, plan “a concrete retaining wall 5 m (16.4 ft) high and 20 m (65.6 ft) long along the road, backfilled behind it,” and estimate material quantities (concrete ○ m³, rebar ○ t) and earth transport volumes. If the road is damaged, calculate pavement and guardrail repair quantities as well.

From this information, estimate the emergency restoration cost and request urgent budget allocation. Speed is especially important in disaster recovery; thus approximate estimates based on experience are often more valuable than precise calculations. Experienced engineers may make immediate judgments on site, and recently the use of photogrammetry and point cloud data analysis allows fast quantity derivation.

For example, if you estimate retaining wall works plus soil removal and road restoration to be on the order of “several tens of millions of yen,” you use this as the basis for budget applications and contractor arrangements. Detailed design and construction stages may require plan revisions based on ground investigation results, but it is important at the approximate design stage to identify the major work items so as not to miss essential elements.

Relationship between field surveys/surveying and approximate design

As described above, approximate design mainly involves desk work, but the relationship with field surveys and surveying is extremely important. Incorporating real site information into desk plans significantly improves the accuracy and reliability of approximate design.

For instance, in approximate design for land development or road planning, the availability of up-to-date survey data greatly influences the accuracy of earthwork calculations. If only old topographic maps or coarse elevation data are available, unexpected ridges or valleys can cause earthwork calculations to be seriously off. Therefore, if possible, perform a simple survey at the approximate design stage or use drone aerial photography to create a current 3D model for reliable terrain understanding.

On-site investigations can uncover issues not shown on drawings. For example, if you find large bedrock exposures while walking the site, you must account for increased cost for blasting or heavy equipment excavation. Or if locals inform you of buried utilities not visible on the surface, you can identify potential additional costs. Such information obtained by visiting the site with your senses is precious supporting data for approximate design.

Surveying technology has also advanced year by year. High-precision surveys that were previously only done during basic surveying or detailed design can now be performed early using simple equipment. Handheld GNSS (high-precision GPS) and simple surveying apps can quickly obtain elevation and position for points. Feeding such survey results back into approximate design helps prevent large discrepancies in quantities later.

In summary, approximate design and field work (site/surveying) go hand in hand. By comparing desk plans with actual site conditions, you can create a feasible plan rather than an unrealistic drawing.

Improving approximate design accuracy with LRTK’s simple surveying feature

In recent years, useful tools for streamlining on-site information gathering have emerged. One such tool is the simple surveying feature provided by LRTK. LRTK is a solution that allows you to easily acquire and share high-precision survey data using a smartphone or a small dedicated device. Using such tools at the approximate design stage can provide significant benefits in both accuracy and speed.

LRTK’s simple surveying feature includes, for example, the following characteristics.

• Photogrammetric positioning: Based on photos taken with a smartphone, you can measure the coordinates of the shooting location and the distance to target objects. This allows you to grasp approximate dimensions and positional relationships on site without spreading tape measures or surveying equipment. It can be used to estimate the scale of a collapse site from photos or to infer elevation differences at a development site from multiple photos.

• Coordinate recording: Using an LRTK device attached to a smartphone, you can record latitude, longitude, and elevation of arbitrary points with one tap. For example, you can walk and measure the edges and center points of a development site or key points along a road route alone and later plot them on a map. Tasks that previously required two people with transit instruments or GPS survey equipment can be done by one person with LRTK.

• Cloud sync: Measured data is immediately saved to the cloud and can be shared in real time with office PCs and colleagues. After obtaining data needed for approximate design on site, you can share it with the team before returning to the office and immediately use it for plan review. This reduces the risk of data loss and automates record organization, improving efficiency.

• Monopod measurement: LRTK is lightweight and compact and can be used mounted on a monopod or pole. This allows one person to acquire stable survey points. In narrow sites or areas with elevation differences, you can quickly measure positions and elevations without carrying heavy tripods or surveying equipment.

• Volume calculation: From multiple points or photo data acquired by LRTK, you can perform simple volume calculations. For example, using point cloud data of measured terrain, the system can automatically compute “how many cubic meters of earth would be moved if you developed this area,” drastically improving the accuracy of earthwork calculations. This is also powerful for estimating landslide volumes at disaster sites.

Using these features improves the quality of approximate design. Planning based on real field data reduces rework and revisions later. It also shortens work time, making LRTK a valuable ally when approximate design must be completed on a tight schedule.

With increasingly user-friendly design support tools for beginners, the cycle of “see the site, measure it, and immediately reflect it in the plan” has become dramatically easier. LRTK’s simple surveying feature is a representative example. If interested, check the [LRTK official site](https://www.lefixea.com/lrtk) to see how it can be used.

Above, we explained the basics of approximate design, concrete examples, and how to use the latest tools. Approximate design is a crucial process that lays the foundation for project success. Learn the basics well and use them to create efficient and accurate plans.