Circle Calculator — Area & Circumference
Know one measurement of a circle? Get the rest. Choose what you know — radius, diameter, circumference or area — and enter its value.
Updated
Formula
Area = πr²
Circumference = 2πr = πd
d = 2r
π ≈ 3.14159. The calculator uses the full-precision value.
Examples
Radius 7 cm
Radius 7 → Area 153.93804, Circumference 43.982297
Diameter 1.2 m
Radius 0.6 → Area 1.130973, Circumference 3.769911
Circumference 100 cm
Radius 15.915494 → Area 795.774715, Circumference 100
Important information
- Measuring a round water tank? Wrap a tape around it for the circumference, then choose 'Circumference' to get the diameter and floor area.
Frequently asked questions
What is the area of a circle with radius 7?
π × 7² ≈ 153.94 square units.
How do I find the radius from the circumference?
Divide the circumference by 2π.
Why use 22/7 for π?
22/7 ≈ 3.1429 is a handy school approximation; the real value is 3.14159…
Related calculators
Pythagorean Theorem Calculator
Math & Statistics
Missing side of a right triangle.
Open calculatorArea Converter
Converters & Everyday
Sq ft, m², sq yd, acres, hectares.
Open calculatorVolume Converter
Converters & Everyday
Litres, gallons, m³, cups and spoons.
Open calculatorScientific Calculator
Math & Statistics
Trig, logs, powers, roots and more.
Open calculatorSquare Root Calculator
Math & Statistics
Square, cube and nth roots.
Open calculatorPlot Size Calculator
Property
Length × width in feet to Marla and Kanal.
Open calculator