ShapesHow to use the calculator
- Choose the shape. The figure shows what each letter means.
- Choose the value of π your book uses, and the unit of your measurements.
- Type the measurements, all in that same unit, and press Calculate.
- Each result comes with its formula and the numbers put in, so you can compare it with your own working line by line.
About the value of π
Text books in India usually ask for π = 22/7, or 3.14 when the numbers suit it. Those give answers a little different from the full value a calculator uses. Choose the same value as your question so that the answers match. The difference is small: for a circle of radius 7 cm the three values give 154, 153.86 and 153.94 cm².
Units
The calculator does not convert between units. It labels the answers: lengths in the unit you chose, areas in that unit squared and volumes in that unit cubed. If your measurements are in different units, change them to one unit first. To turn a volume into litres, remember that 1000 cm³ make a litre and 1 m³ is 1000 litres. See units of area and volume.
What it checks
It refuses measurements that cannot make the shape: three sides that do not form a triangle, an inner radius larger than the outer one, or a slant side shorter than the height. Answers are rounded to two decimal places. The perimeter of an ellipse is an approximation, as every simple formula for it is.
For homework
Work the sum yourself first and use the calculator to check. If the answers differ, compare the working line shown under each result with yours: the usual causes are the diameter used as the radius, a slant height used as the height, or a different value of π. Your measurements stay in your browser and are not sent anywhere.