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Diameter to Circumference

Enter a diameter and we'll multiply by π to give you the circumference. The simplest circle formula there is.

Circumference
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Diameter to circumference formula

The circumference of a circle equals its diameter multiplied by pi:

C = π · d

That's literally the definition of pi — the ratio of a circle's circumference to its diameter is π ≈ 3.14159265358979… for every circle ever drawn. Whether you're sizing a wheel, a pizza, the Moon, or a CERN particle collider, the relationship is the same.

Worked examples

  • Diameter 10 cm → Circumference 10π ≈ 31.4159 cm
  • Diameter 12 in → Circumference 12π ≈ 37.6991 in
  • Diameter 1 m → Circumference π ≈ 3.14159 m

Going the other way

If you already know the circumference and need the diameter, just divide: d = C / π. And if you'd rather work from the radius instead, see our circumference calculator.

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