Work out area, perimeter, and volume for the shapes people actually measure: rectangles, triangles, circles, and cylinders. Includes Heron’s formula.
What units does this use?
Whatever you type. The maths does not care, so metres give square metres and feet give square feet. The only rule is not to mix units inside one shape. Use the unit converter first if your measurements are in different units.
How do I find the area of a triangle without the height?
Use Heron’s formula, which needs only the three side lengths. Switch the triangle mode on this page to "three sides". It is what surveyors use for an irregular plot where no height is easy to measure.
Why do my three side lengths get rejected?
Because they cannot close into a triangle. Any side has to be shorter than the other two added together. Sides of 1, 2, and 10 will never meet, and sides of 2, 3, and 5 lie flat in a straight line with no area at all.
How many litres does my tank hold?
Measure in centimetres and divide the volume by 1,000, which this page does for you. A tank with a 30 cm radius and a 100 cm height holds about 282.7 litres.
What is the difference between curved and total surface area?
The curved surface is just the side you would wrap a label around. The total adds both circular ends. Use the curved figure for a label and the total for paint.
How do I measure an odd shaped room?
Split it into rectangles and triangles, work out each piece, and add them. Almost every irregular floor plan is two or three simple shapes stuck together.