Methodology
How we calculate area
Our methodology for the Area calculator: the formula, step-by-step calculation, authoritative sources, and limitations. Reviewed quarterly.
Formula
varies by shape (A = l × w for rectangles; A = πr² for circles; etc.)
Step-by-step
- 1
Identify the shape (rectangle, triangle, circle, etc.).
- 2
Measure the required dimensions (length, width, radius, base, height) in consistent units.
- 3
Apply the shape-specific formula:
- 4
Rectangle: A = length × width
- 5
Triangle: A = ½ × base × height
- 6
Circle: A = π × radius²
- 7
Trapezoid: A = ½ × (base1 + base2) × height
- 8
Ellipse: A = π × semi-major × semi-minor
- 9
Convert units if needed. 1 m² = 10.764 ft². 1 acre = 43,560 ft².
Authoritative sources
Every claim on this page is backed by an authoritative source.
Assumptions
What we take to be true when applying this formula.
-
All measurements are accurate to the precision needed for the use case.
-
The shape is regular (sides are straight, angles are as expected). For irregular shapes, decompose into regular shapes.
-
Units are consistent. Convert before calculating, not after.
Limitations
What this method does NOT capture.
-
For complex 2D shapes (L-shaped rooms, curved boundaries), use polygon decomposition or CAD tools.
-
Surface area is the 3D equivalent — for floor area of a multi-level building, sum the floor plates.
-
For land measurement, professional surveys are more accurate than tape measures.
Last reviewed: 2026-06-15 • Reviewed by: CalcxApp editorial team