Area calculator
Choose a shape, enter its measurements and get its area.
Area
Area: 40
- Perimeter
- 26
How it works
Area measures the flat surface inside a shape, in square units. Rectangles and parallelograms are base × height; a triangle is half of that.
A trapezoid is the average of its two parallel sides times the height. A circle is πr², an ellipse πab, and a sector is the fraction θ/360 of a full circle.
The height is always measured at right angles to the base, not along a slanted side.
Formula
rectangle = l × w triangle = ½ × base × height parallelogram = base × height trapezoid = ½(a + b) × h circle = πr² ellipse = πab sector = θ ÷ 360 × πr²
Worked example
A rectangle 8 by 5 has an area of 40 and a perimeter of 26. A trapezoid with parallel sides 6 and 10 and height 5 also has area ½ × (6 + 10) × 5 = 40.
Questions people ask
What units is the area in?
The square of the length unit you used: metres in, square metres out.
How do I find the area of an irregular shape?
Split it into rectangles, triangles and circle parts, work out each area and add them up.
Which height do I use for a triangle?
The perpendicular distance from the base to the opposite corner, which may fall outside the triangle for obtuse shapes.