Construction Cost Calculator

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What is Construction Cost?

This construction cost calculator builds a preliminary estimate from floor area, a cost per square foot, and the number of floors. It also applies a fixed multiplier when you select Finishing. The calculation is intended for comparing simple area-and-rate scenarios, not measuring materials from drawings.

The most important choice is what your area represents. The calculator multiplies Covered Area by Number of Floors. Enter the area of one typical floor when all floors have the same size. If you already know the total area across the building, enter that total with a floor count of one to avoid multiplying it twice.

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How to Use This Calculator

Choose Grey Structure or Finishing, then enter the covered area in square feet or square metres. The calculator converts square metres to square feet internally. The Cost per sq ft input always remains a rate per square foot, even when the area is entered in square metres.

Enter a scope-matched rate and the floor count, then choose Calculate. The result is rounded to a whole monetary unit and displayed with a dollar sign. There is no currency selector or exchange-rate conversion.

Before using Finishing, note how this page implements it: the same area-times-rate calculation is increased by 20%. It does not calculate a separate list of finish items or isolate a finishing-only budget. If you already have a complete quoted rate including finishes, using this multiplier can add an allowance you did not intend.

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Formula Used

Base estimate B = A × c × f, where A is covered area in square feet, c is cost per square foot, and f is the floor count. Grey Structure returns B. Finishing returns 1.20 × B.

For an area entered in square metres, the implementation first uses A = area in m² × 10.7639. This is a rounded conversion factor. A rate quoted per square metre must be converted independently before entry: divide that rate by approximately 10.7639 to obtain a rate per square foot.

The 20% adjustment is a built-in scenario assumption. It is not derived from your design, location, supplier prices, or a professional quantity survey. Changing construction type therefore changes a multiplier, not the underlying project specification.

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Variables Explained

Symbol or inputMeaning in this calculator
Construction TypeGrey Structure uses the base estimate; Finishing multiplies it by 1.20.
Covered Area AArea per typical floor, unless you enter the building total and set floors to one.
Cost per sq ft cMonetary amount for each square foot on the same scope and measurement basis as the area.
Number of Floors fMultiplier for equally sized floors. Use separate calculations for unequal areas when appropriate.
Total estimateArea × rate × floors, with the selected type multiplier and whole-unit display rounding.
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Worked Example

Suppose two floors each have 1,000 ft² of covered area. Use an illustrative rate of 150 per ft², select Grey Structure, and enter two floors. The total covered area represented is 2,000 ft². The estimate is 1,000 × 150 × 2 = 300,000.

With the same inputs and Finishing selected, the page multiplies 300,000 by 1.20 and returns 360,000. The additional 60,000 is the calculator's fixed 20% adjustment. It is not an independently measured bill for flooring, paint, fixtures, or joinery.

If your drawings instead show 1,000 ft² downstairs and 700 ft² upstairs, their combined area is 1,700 ft². Enter 1,700 with one floor, using the same 150 rate, to obtain a Grey Structure estimate of 255,000. Entering 1,700 and two floors would incorrectly double the building area.

For a unit check, 100 m² converts here to 1,076.39 ft². At 150 per ft² and one floor, the mathematical base estimate is 161,458.50. The current calculator displays 161,458 in this case because of floating-point rounding at the half-unit boundary; retain the unrounded calculation if that last unit matters.

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Why Use This Calculator?

The result is only as useful as the unit rate behind it. Record the source date, location, scope, and area definition of that rate beside your estimate. A rate for internal floor area should not be applied casually to a larger external area measurement, and a shell-only rate should not be described as a complete move-in budget.

The form has no separate entries for land, professional fees, permits, demolition, unusual ground conditions, external works, financing, taxes, or contingency. Whether any of these are included depends entirely on the rate you entered. List exclusions explicitly when sharing an estimate so another person can compare like with like.

Compare design scenarios by changing one input at a time. Real project costs may not scale exactly with area: some costs are fixed, while others depend on complexity.

A measured cost plan or contractor quotation needs more detail than this multiplication. RICS cost-planning guidance provides a framework for documenting scope and estimates; the calculator itself does not implement that full framework.

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Common Mistakes

    Avoid counting all-floor area once in Covered Area and again through Number of Floors. Avoid entering a square-metre rate into the square-foot price field. Do not read the Finishing option as a universal statement that finishing costs are 20% higher or as a separate finishing-only total.

    Use rates in one currency throughout your own comparison. The dollar symbol is a display label, not evidence that a local rate was converted to dollars. Also, the form accepts numeric floor values, but a fractional entry should not replace a proper calculation of unequal floor areas.

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Frequently Asked Questions

Should I enter plot area or covered floor area?

Enter the area represented by your construction rate, normally the covered building area under its stated measurement convention. A plot may include a garden, driveway, and setbacks that are not equivalent to constructed floor space.

Can I use square metres for both area and price?

The area selector supports square metres, but the price field remains per square foot. Convert a per-square-metre price by dividing by approximately 10.7639 before entering it.

Does Finishing give the cost of finishes alone?

No. It returns 120% of the same base estimate. It does not subtract a structural cost or measure individual finish items, so its label should not be interpreted as a separate finishing quotation.

How do I account for different floor sizes?

Add the relevant floor areas and use one as the multiplier, or calculate each floor separately and combine the estimates. Separate calculations also help when the floors need different unit rates.

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Sources & References

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