Area calculator
Pick a shape, type its sizes and see the area right away, along with a diagram and the formula.
How it works
- Pick the shape. For some shapes you can choose what you know, such as the radius or the diameter of a circle.
- Choose the unit and type the sizes shown in the diagram. A comma or a dot both work.
- Read the area in your unit squared and in other units. Open All units for the full list.
How area is worked out
Area is how much flat surface a shape covers. A rectangle is the easy case: length times width. A triangle is half of that: base times height, divided by two. A circle uses π (about 3.14159) times the radius squared.
When you only know the three sides of a triangle, Heron's formula still finds the area. First take half the perimeter, called s, then the area is the square root of s(s − a)(s − b)(s − c). It only works if each side is shorter than the other two together, otherwise the sides cannot meet.
Units matter: if you measure in centimetres, the area comes out in square centimetres. One square metre is 10 000 square centimetres, not 100, because both the length and the width are 100 times bigger.
Measuring square metres for flooring, paint and gardens
Most people need area for a job around the house: how much laminate for a room, how many tiles for a bathroom, how much paint for a wall, or how much grass seed for a lawn. Measure in metres, split odd shapes into rectangles, triangles and circles, work out each part and add them up.
For walls, multiply the width by the height and subtract windows and doors. Buy about 10 percent extra flooring or tiles for cutting and mistakes, and more for diagonal patterns. Check the packaging, which usually says how many square metres one pack or one litre of paint covers.
Choose the unit you measured in. If you mix units, such as a length in metres and a width in centimetres, convert one of them first, or the answer will be far off. The result is shown in other units too, so you can read square metres and square feet side by side.
Questions
How do I calculate the square metres of a room?
Measure the length and width in metres and choose Rectangle. A room of 4,5 by 3,2 m is 14,4 m². For an L shaped room, split it into two rectangles and add the areas.
How do I convert cm² to m²?
Divide by 10 000. The calculator shows the result in other units automatically, and All units lists them all.
Why does my triangle give an error?
Three sides only make a triangle if every side is shorter than the other two added together. With sides 2, 3 and 10, the short sides cannot reach each other.
What is a sector?
A slice of a circle, like a piece of pie. Its area is the angle divided by 360, times the area of the whole circle.
How do I calculate the area of a round table or pond?
Choose Circle and type the radius or the diameter. A circle 2 m across covers about 3,14 m².
How do I calculate square feet?
Type your sizes in feet, or in metres and read the result in ft². One square metre is about 10,76 square feet.
Which shapes are included?
Square, rectangle, circle, triangle, trapezoid, parallelogram, ellipse, ring, regular polygon and sector.
Something not working, or a tool you miss?