circumference

Everyday

1. (maths) The distance all the way around the edge of a circle; the perimeter of a circle. tree →
2. The distance around anything round: the circumference of a tree trunk, of the Earth. tree →
3. The edge or boundary of a round area. tree →

In the lessons

In maths lessons the circumference is found with C = pi x d (pi times the diameter) or C = 2 x pi x r, using pi of about 3.14. In science and geography the Earth's circumference is about 40,000 km. Phrases: the circumference of, measure the circumference, find the circumference.

Examples

• The circumference is the distance around a circle. tree →
• A circle with a diameter of 10 cm has a circumference of about 31.4 cm. tree →
• Measure the circumference of a tree with a tape measure. tree →
• The Earth's circumference is about 40,000 kilometres. tree →
• Wrap a string around the tin to find its circumference. tree →
• (formal) Calculate the circumference given a radius of 7 cm (about 44 cm). tree →
• Its ring was broad, and from its circumference the rays shot like whirling shafts of fire across the whole sky, flashing in changing radiance from green to red. tree →

Note

Countable; usually "the circumference". Formula: C = pi x diameter = 2 x pi x radius. Traps: do not mix up radius and diameter (diameter = 2 x radius); do not confuse circumference (a length, in cm) with area (in square cm, pi x r x r).