How to use
- Start with a rectangle, triangle, or circle for the first part of your room.
- In US mode, put whole or decimal feet in the feet field and any remaining inches in the adjacent field. Use decimal meters in metric mode.
- Add another shape for each non-overlapping section, then calculate the combined area.
- Remove unused rows; an empty shape is not automatically skipped.
How the estimate is calculated
A rectangle contributes length × width. A triangle contributes base × perpendicular height ÷ 2, and a circle contributes π × (diameter ÷ 2)². Adding those contributions gives the combined square footage. Feet and additional inches are combined before multiplication: feet + inches ÷ 12.
Example: a 20 ft × 15 ft rectangle contributes 300.0 sq ft. An adjoining triangle with a 10 ft base and 6 ft perpendicular height adds 30.0 sq ft. The total is 330.0 sq ft, or 30.7 m² and 36.7 sq yd. There is no waste allowance in this geometric total.
Area conversion reference
| Starting quantity | Converted quantity | Basis |
|---|---|---|
| 1 sq ft | 0.09290304 m² | 0.3048 m squared |
| 1 sq yd | 9 sq ft | 3 ft × 3 ft |
| 1 acre | 43,560 sq ft | Conventional land-area conversion |
| 1 in | 2.54 cm exactly | NIST length definition |
Length definition: NIST SI Units — Length. Square-meter and square-yard factors follow by squaring length factors. The acre conversion is used here as a conventional planning figure.
Measuring an L-shaped room
Sketch the boundary and draw a dividing line at the inside corner to create two rectangles. Label the separate lengths, rather than using the overall length twice. Count a closet as another rectangle if it belongs in your project. A bay window may be a rectangle plus triangles; measure the triangular height perpendicular to its base, not along the sloping side.
Keep each piece inside the boundary and avoid shared area. The calculator adds shapes; it cannot see overlap in your sketch. For a material order, take the finished area to the relevant paint or flooring estimator and apply the material-specific allowance there.
Common mistakes
- A triangle’s sloping edge is not its perpendicular height.
- Do not type 12.6 to mean 12 ft 6 in; that decimal is 12 ft plus 0.6 ft. Use the separate inches box.
- A circular row takes diameter, not radius. Entering radius would produce one-quarter of the intended circle area.
- A hole or stairwell is not a negative shape in this tool. Measure the remaining floor as separate positive pieces.
Sources
Exact inch-to-centimeter definition: NIST SI Units — Length, used as the length-conversion basis. Shape formulas are elementary geometry. Acres are shown with a conventional conversion rather than an unverified standards citation.
Related calculators
- Paint Calculator — room walls and ceiling
- Drywall Calculator — turn room dimensions into sheets
- Roof Pitch Calculator — horizontal area versus sloped area
Frequently asked questions
Can I enter feet and inches together?
Yes. Enter feet in the main dimension field and the remaining inches beside it. A value of 6 in the inches box adds half a foot.
How do I measure a curved section?
Use a circle only when the whole section is circular. For a more complex curve, divide it into measurable approximations and record that the result is approximate.
Does this total include closets?
Only if you add them. Whether a closet belongs in the reported area depends on the purpose of your measurement.
Can the calculator subtract openings?
It adds positive shapes only. Split the area around an opening into non-overlapping rectangles or triangles before entering it.