How it works
Calculate area in square feet or square meters for rectangles, triangles and circles — add several rooms and a waste allowance for material planning.
Choose a shape and a length unit, then enter the dimensions. Lengths are normalized internally, so every shape and unit shares one formula: rectangle = length × width, triangle = base × height ÷ 2, circle = π × (diameter ÷ 2)². In rectangle mode you can add further rooms as comma-separated pairs such as 12x10, 8x9. An optional waste allowance adds a percentage on top of the measured area; it is never assumed for you.
Formula
Rectangle: A = L × W · Triangle: A = b × h ÷ 2 · Circle: A = π × r². Units are converted through meters (1 ft = 0.3048 m, 1 in = 0.0254 m, 1 cm = 0.01 m).
L, W- Rectangle length and width (selected unit)
b, h- Triangle base and height (selected unit)
d- Circle diameter (selected unit)
w- Optional waste allowance (%)
Examples
- 15 × 20 ft roomShape rectangle · unit ft · length 15 · width 20300 ft² = 27.87 m²
- Two extra rooms and 10% waste10 × 10 ft plus rooms 5x4, 3x2 · waste 10%Base 126 ft² · waste 12.6 ft² · total 138.6 ft²
Frequently asked questions
How do I add several rooms?
In rectangle mode enter one length and width above, then list the other rooms in the additional-rooms field as pairs like 12x10, 8x9. All values use the selected unit.
What waste percentage should I use?
There is no universal value: it depends on the material and the layout. Enter the allowance your supplier or installer recommends; the tool does not assume one.
Which units are supported?
Feet, meters, inches and centimeters. The result is shown in square feet, square meters and the selected unit.
Does circle mode use diameter or radius?
Diameter — the radius is half of it and is used inside the formula.
Is this a floor-plan tool?
No. It sums measured areas; it does not draw or validate room layouts.
How to read the result
The base area is the measured surface. The waste line is an allowance for cutting, offcuts and spares, and the total is what you should plan to buy. Use the unit you measured in and double-check that mixed rooms are all in the same unit.
Limitations
Assumes straight measured dimensions and regular shapes. Irregular rooms should be split into simpler shapes and added as rooms. Waste percentages are user-supplied, not recommendations.
Source: Standard geometric area formulas; exact unit conversions (1 ft = 0.3048 m).