Area measures a two-dimensional surface. The appropriate formula depends on the shape and the available measurements.
The underlying idea
Rectangle: length × width. Triangle: base × height ÷ 2. Circle: π × radius². Break compound shapes into nonoverlapping pieces and add their areas.
Match the formula to the shape
Rectangle: length × width. Triangle: base × height ÷ 2. Circle: π × radius². Break compound shapes into nonoverlapping pieces and add their areas. Choose measurements that describe the same object, system, or period; changing the reference changes what the result means.
Worked example
A 6 by 4 rectangle has area 24 square units. A triangle with the same base and perpendicular height has half that area: 12 square units.
Put the method into practice
- Write down the quantity you need to find.
- Identify the measurements and their units.
- Convert units before doing the calculation.
- Apply the formula and keep unrounded intermediate values.
- Check whether the result is reasonable for your situation.
Try the Area Calculator with your own values.
Common mistakes
Mixing units, using the wrong reference value, and rounding too early can all change the result. A calculator cannot repair inaccurate measurements. For project estimates, distinguish the calculated base quantity from allowances and supplier rounding.
What to learn next
Explore this topic’s related answers below for focused examples and alternative ways to check a result.
