Area Calculator

Start with one measurement unit

Area calculation tells you how much two-dimensional space lies inside a boundary. Before selecting a shape, convert every length to the same unit. Metres produce square metres, centimetres produce square centimetres, and 1 m² equals 10,000 cm². Mixing a length in metres with one in centimetres gives a different error: one factor, rather than both, has the wrong scale.

A rectangle needs length and width. For a square, multiply its side length by itself. For a 5 by 4 rectangle the result is 20 units²; for a square with side 5 it is 25 units². Those formulas assume right angles, so they should not be used for a visibly slanted outline.

A triangle needs a base and the height perpendicular to it. A sloping side is not that height. If the height cannot be measured but all three sides are known, the Heron mode first finds the semiperimeter s = (a + b + c) / 2 and then evaluates A = √(s(s-a)(s-b)(s-c)). The two shorter sides must add to more than the longest. For sides 3, 4 and 5 cm, s = 6 cm and the area is 6 cm².

Four sides do not fix a unique area

Four side lengths alone do not normally fix the area of a quadrilateral. Different angles can produce different enclosed areas with the same sides. Trapezoid mode therefore asks for two parallel bases and their perpendicular separation; rectangle and parallelogram modes make their own geometric assumptions. An irregular quadrilateral may require a diagonal, angle, height or vertex coordinates.

Radius, square metres and irregular floors

A circle uses A = πr². Radius r runs from the centre to the edge; if you have the full diameter, halve it first. Area describes the filled region; circumference measures its boundary. The semicircle mode divides the full circle area by two. For an ellipse, use half of each full axis: a 12 by 8 oval has semiaxes 6 and 4. Its area formula πab is exact, though the displayed decimal is rounded.

For an area in square meters, enter all lengths in metres. A 250 cm side is 2.5 m, so a 2.5 m by 4 m floor covers 10 m². One square metre equals 10,000 cm². Surface area adds the exposed faces of a three-dimensional solid; this page handles flat shapes only.

For an L-shaped room, split the plan into non-overlapping rectangles or triangles. Add the occupied pieces and subtract recesses. This is often clearer than forcing the outline into one formula, and the calculation line beneath the result lets you check which measurements were actually used.

Use 1.5 for a decimal measurement or 1,500 for fifteen hundred, without spaces or unit labels. The browser calculates with about 15–17 significant digits. The main value shows up to six decimal places and the copied value up to ten; extreme values use scientific notation. Rounded figures in the working are for display, not reused in the calculation. Results outside the number range, including positive areas that round to zero, are rejected. A geometric total does not establish a legal floor area or replace a land survey.