Square footage calculator results give measured area from room or shape dimensions, with feet-and-inches entry, multiple sections, metric equivalents, and optional allowance and price.
Measure square footage from the right dimensions
For a rectangle, multiply length by width after converting both dimensions to the same unit. Square dimensions use side squared; circular areas use the radius squared multiplied by pi. Triangle base-height mode requires the perpendicular height. Three-side mode uses Heron’s formula and rejects sides that cannot form a triangle. Trapezoids require parallel bases and the perpendicular distance between them. The formulas follow OpenStax’s geometric formulas. Choose an entry path that matches the measurements you have: circle and ring diameters go across the center, border dimensions describe the inside opening, and border width is added outward. A sloped roof needs dimensions on its actual surface rather than an unadjusted ground footprint.
A bounding rectangle includes empty corners. For an L-shaped room, add separate rectangles that do not overlap.
Each ordinary dimension has its own unit selector. Feet-and-inches entry uses separate components.
Measured, planned and purchased area are different quantities.
Square Footage Calculator example
- Enter 12 for length and 12 for width.
- The measured area is 144 sq ft; the metric equivalent is 13.3780378 m².
- The result remains measured area until you enter an optional allowance.
Common area conversions
These equivalents come from the same area engine, using exact NIST unit definitions and display rounding only.
| Square feet | Square meters | Square yards | Acres |
|---|---|---|---|
| 1 | 0.09290304 | 0.111111111 | 2.29568411e-5 |
| 9 | 0.83612736 | 1 | 0.00020661157 |
| 144 | 13.3780378 | 16 | 0.00330578512 |
| 43,560 | 4,046.85642 | 4,840 | 1 |
Customary units use the international foot. Displayed decimal equivalents may be rounded.
Feet and inches without decimal mistakes
Choose Rectangle · feet and inches when your tape uses mixed components. Enter the whole feet and remaining inches separately. A length of 12 7 and width of 10 3 produce 128.979167 sq ft, not the area obtained by treating the measurements as decimal feet.
When entering total inches instead, convert the squared result, not just one dimension: a 12 by 12 surface is 1 sq ft. NIST’s unit tables establish the length and derived area factors.
Combine sections and subtract cutouts
Sketch irregular rooms as simple sections. Multiple sections accepts rectangles, triangles and circles, with an Add or Subtract choice on each row. Use the full diameter for a circular section and perpendicular height for a triangle. A 12 by 10 main rectangle plus a 6 by 4 alcove totals 144 sq ft.
Count each included patch once. Subtract only a cutout already inside an added section, and do not enter it again as an additional excluded area. Identical copies repeats the entire selected plan before the additional deduction. For a lot whose corners or angles are unknown, side lengths alone can be insufficient; this tool does not supply missing survey measurements.
For a wall, use its width and height as the rectangle dimensions. A 12 wide, 8 high wall has a 3 by 7 opening measuring 21 ; enter that opening as an additional exclusion to get 75 sq ft of remaining wall surface. Do not also subtract the same opening in the section list.
Convert the measured area and plan a purchase
The primary answer is measured square footage. Metric and square-yard equivalents describe the same surface; they do not add an allowance. Acres are available in calculation details for simple land measurements, using NIST’s international-foot definitions.
More options keeps excluded area, identical copies, an editable allowance and your quoted price separate. With an entered 10% allowance, the example room plans 158.4 (10% extra). An entered price of 2 per square foot gives 316.80 entered currency units using only the entered quote; no tax, labor or delivery amount is added separately. No local price or standard allowance is assumed.
When the next step is an order, packaged flooring needs whole-package rounding, broadloom carpet needs a roll-width and seam plan, and tile needs piece and box counts. Paint coverage also depends on coats and the product’s stated rate; a flat area by itself cannot supply those inputs.
For garden or land work, Topsoil Calculator adds the required depth to turn a footprint into volume. Linear Feet Calculator uses a material width to turn an already-measured area into length; a length alone does not determine square footage.
The distance around an outside boundary is a separate measurement. Perimeter Calculator uses its sides or circular dimensions; equal areas can have different boundary lengths.
When the area is already known, Area Converter changes its units directly, including acres and hectares; no shape dimensions are needed.