Landscape & Groundwork
Square Footage Calculator
Measure rectangle, triangle and circle areas, or combine rectangular and triangular sections.
Enter your measurements
Results update as you type.
About this calculator
Measure rectangle, triangle and circle areas, or combine rectangular and triangular sections. Enter the measurements for the selected mode and compare the worked example below. The result describes geometry only.
How to measure
- Measure the actual usable surface or internal space, using the field labels for the selected mode.
- Keep openings and excluded areas separate so they are subtracted once.
- Recheck units and label coverage before ordering.
How to use this calculator
- Choose rectangle, triangle, circle or Combine sections.
- Enter dimensions in the labelled units; use a perpendicular height for triangles.
- In Combine sections, add non-overlapping rectangular and triangular parts.
- Subtract excluded area once and read the net area in the displayed units.
Formula
Rectangle = length × width; triangle = base × perpendicular height ÷ 2
Circle = π × diameter² ÷ 4
Net area = sum of non-overlapping sections − exclusions
Assumptions
- All component shapes are planar and do not overlap.
- Triangle height is measured perpendicular to its base; the circle input is diameter.
- Exclusions are deducted once. There is no product yield, waste allowance or purchase-unit count in this model.
Common mistakes
- Applying the same allowance in both measurements and the extra-material field.
- Entering coverage or yield from a different product or measurement basis.
- Treating a quantity estimate as an installation or structural approval.
Worked example
Try it: press “Load example” above the form.
A 10 × 12 ft rectangle is 120 ft². In Combine sections mode, adding a triangle with 6 ft base and 4 ft perpendicular height gives another 12 ft², for 132 ft² total.
Limitations
Use non-overlapping shapes and perpendicular triangle heights. Curved and irregular boundaries require an appropriate geometric or surveyed model. This is not a property survey.
Frequently asked questions
How do I measure a triangle or combine an irregular area?
A triangle uses base times perpendicular height divided by two. For an irregular outline, choose Combine sections and add non-overlapping rectangular or triangular parts. Deduct exclusions once.
What does the worked example show?
A 10 × 12 ft rectangle is 120 ft². In Combine sections mode, adding a triangle with 6 ft base and 4 ft perpendicular height gives another 12 ft², for 132 ft² total.
Does this replace a property survey?
No. It calculates area from your entered planar shapes and exclusions. Boundaries, terrain and legal parcel areas require appropriate surveyed information.
What are the limits for curved or sloping boundaries?
Use non-overlapping shapes and perpendicular triangle heights. Curved and irregular boundaries require an appropriate geometric or surveyed model. This is not a property survey.
Sources
Sources explain the methods and any named product presets. Check your product label where coverage, yield or density differs.
- NIST: Revised Unit Conversion Factors
- Defined geometric and purchase-quantity model
Formulae on this page define the arithmetic model. Worked examples are illustrative, not product or installation recommendations.
Calculation documentation · Updated 2026-11-11 · Version 1.6.4. Estimates are planning aids. Confirm quantities, coverage and prices with your supplier before purchasing. Found an error? Report it.
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