How this calculator works
A square metre is a square one metre on each side. For a rectangle multiply the two side lengths; for a circle use pi times the diameter squared over four, or pi times the radius squared. A triangle from three sides uses Heron's formula, and a regular polygon uses its side count and side length. Mixed input units are converted to metres before multiplying, so a wall measured in millimetres and metres still gives a correct square-metre figure. The square-foot and square-yard rows use exact factors: one square foot is 0.09290304 m2 and one square yard is 0.83612736 m2.
Formula
Square = side^2; rectangle = length x width; circle = pi x diameter^2 / 4; triangle from sides a, b, c: s = (a + b + c)/2 and area = sqrt(s(s-a)(s-b)(s-c)); regular n-gon = (n/4) x side^2 / tan(pi/n). Square feet = m2 / 0.09290304; square yards = m2 / 0.83612736.
Worked example
A rectangle 5 m by 4 m is 20 m2, 215.28 ft2 and 23.92 yd2. A 3 m circle is 7.07 m2. A regular hexagon with 2 m sides is 10.39 m2, because its area is (6/4) x 4 / tan(30 degrees).
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Frequently asked questions
Is a square metre the same as a metre squared?
Yes. Both mean the area of a square one metre on each side. Confusingly, a metre squared could be read as the square of a length, which is exactly what calculating area does.
How do I measure an irregular room?
Split it into rectangles and triangles, measure each one, and add the areas. A single average width is less reliable than two or three measured shapes.
Why does the result sometimes differ from a conversion app?
Conversion apps round early. Square feet are about 10.76 times square metres, and this tool keeps full precision until it displays the answer, so small differences are display rounding only.