Circumference

Japanese school year: Elementary 5

What you learn

Learn the meaning of pi and the formula to calculate the circumference of a circle from its diameter. This calculation is used when determining tire distances or measuring circular columns. Prior understanding of the relationship between radius and diameter, along with mastery of decimal multiplication, will ensure smooth calculations.

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Key points

This formula finds the diameter d of a circle. Multiply the radius r by 2.

d = 2r

This formula finds the circumference $\ell$ of a circle. Multiply the diameter $2r$ by pi $\pi$ .

\ell = 2\pi r

This formula shows what pi π means. Divide circumference ℓ by diameter d; it is the same for all circles.

\pi = \frac{\ell}{d}

This shows the approximate value of pi π. In math, we usually calculate using about 3.14.

\pi \approx 3.14

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Practice 1Coming soon