The most common question when building a house or building is "what's the budget?" Some contractors answer with a price per square meter; others ask for the drawings to take off a BOQ before quoting. How do these two figures differ, and which should you trust? This article explains what a BOQ is, the steps of quantity take-off and cost estimation, and why the design must be completed before you can know the real price.
What is a BOQ (Bill of Quantities)?
A BOQ, or bill of quantities, is a document that breaks down the construction work of an entire project into individual items, stating the quantity, unit, material cost and labor cost of each item, up to the total price. It is produced by a "take-off" — reading the construction drawings and measuring the actual quantities section by section, from piling and foundations and RC structural work to architectural work and electrical/plumbing systems.
In practice, a BOQ is used at 3 key stages: to set the budget and make decisions before construction, to compare each contractor's quotation line by line, and as the basis for progress payments during construction — so a single document controls the money throughout the project. For an overview of the design work that a BOQ starts from, read Guide to RC structural and civil engineering design.
How does a BOQ differ from a price per square meter?
A per-square-meter price is a rough estimate — floor area multiplied by an average rate — while a BOQ is an item-by-item take-off from the actual drawings. The first is fast but can be far off; the second is detailed and can be used to bind the price with a contractor. The differences are summarized in the table.
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| Topic | Price per m² | BOQ (take-off) |
|---|---|---|
| Method | Floor area × average price per m² | Take off quantities from the drawings item by item, then apply material + labor unit rates |
| Resolution | A single lump figure, no detail | Every item and work section, with quantities and units |
| Accuracy | Can be far off, as it does not reflect material specs and actual details | As accurate as the drawings are complete; usable to agree the actual price |
| Documents required | No drawings needed — floor area alone is enough | Full set of construction drawings + specifications |
| Use | Preliminary budget, feasibility study | Tendering, comparing contractor prices, contracts, progress payments |
| Best suited to | Before drawings exist / early project concept | After design is complete, before selecting a contractor |
The two methods do not replace each other — they are used at different stages. At the project concept stage, a per-square-meter price sets a rough budget; once the drawings are complete, a BOQ is taken off to get the real figure. Problems arise when a per-square-meter price goes straight into a contract: during construction the specs do not match what each party had in mind, and variation orders follow endlessly.
What are the steps of a BOQ take-off?
Preparing a BOQ has 4 main steps: read the drawings, take off quantities, apply material and labor rates, then compile the document. Each step in detail:
- Read the drawings and specifications: review the architectural, structural and MEP drawings in full, check the specified materials, and check whether each drawing set is consistent. Any conflicts between drawings must be clarified with the designer before the take-off.
- Quantity take-off: measure quantities from the drawings section by section — e.g. cubic meters of concrete, kilograms of reinforcing steel, square meters of masonry wall — organized by work section so they can be traced back.
- Apply material and labor rates: multiply quantities by unit rates, referencing market material prices or the standard price lists published by the relevant agencies, with separate columns for material and labor costs.
- Compile the BOQ: sum all sections into a total price, add overheads, profit and taxes according to the agreed price structure, giving a document ready for tendering or contracting.
What does a BOQ table (BOQ sheet) look like?
One row of a BOQ sheet contains the work item, quantity, unit, material unit rate, labor unit rate and the total price of that item, grouped into work sections such as piling, structural, architectural and MEP work. The example below is the structural section of a hypothetical 2-storey house, to show what the actual document looks like.
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| No. | Item | Qty | Unit | Mat./unit | Labor/unit | Total (THB) |
|---|---|---|---|---|---|---|
| 1 | Prestressed concrete pile I-22, 21 m long (incl. driving) | 30 | pcs | 6,000 | 1,500 | 225,000 |
| 2 | Structural concrete, compressive strength 240 ksc | 85 | m³ | 2,200 | 500 | 229,500 |
| 3 | Reinforcing steel SD40 | 9,500 | kg | 24 | 4 | 266,000 |
| 4 | Formwork + shoring | 560 | m² | 180 | 120 | 168,000 |
| 5 | Sand fill for leveling, compacted | 45 | m³ | 350 | 80 | 19,350 |
| Structural section total | 907,850 | |||||
⚠️ Every figure in the table is hypothetical. Actual material and labor prices depend on specs, location, timing and each contractor — do not use them as market price references. The point to note is the document structure: every item can be traced back to the drawings, and material and labor costs are separated, so contractor quotations can be compared line by line to see whether one is expensive on materials or on labor.
Why must the structure be designed before a BOQ can be prepared?
Because a BOQ is a direct take-off from the drawings — no drawings means nothing to take off. The quantities of concrete and reinforcing steel and the foundation sizes all come from the engineer's design. Until the structure is designed, any figure is just a guess.
The correct sequence therefore starts with a soil investigation so the engineer has data to design the foundations, followed by architectural and structural design with a structural calculation report. Only when the full drawing set is complete can a BOQ be taken off with figures that match reality. Soil data directly affects cost — for example, deep soft soil layers require longer piles, and the foundation quantities in the BOQ change accordingly. See our soil investigation and testing and civil engineering design services.
The complete drawings are also the same set used to apply for a building permit from the relevant authority — see the building permit process. Investing in completing the design first gives you both the permit and a controllable budget in one go.
Who should prepare the BOQ?
A BOQ is generally prepared by a quantity surveyor (QS) / estimator, engineer or architect on the design side, while each contractor takes off its own quantities to submit a competitive bid. An owner with their own reference BOQ can compare quotations fairly and see immediately which items from which contractor are abnormally cheap or expensive.
For residential projects, homeowners do not need to do the take-off themselves, but they should ask every bidding contractor for a BOQ and have the designer or a consultant check that the items are complete and the quantities reasonable. For the design-side costs that a BOQ starts from, read How RC structural design fees are priced.
This article explains cost-estimating principles for general understanding only. Material prices, labor costs and conditions differ from project to project. Preparing or certifying a BOQ and designing each building must be carried out by the licensed professionals directly responsible for that project.