THE IDEA BEHIND THE ANSWER
A formula you can follow.
area = πr² · circumference = 2πr
The diameter is twice the radius. Select which one you measured before calculating.
SHAPES & EVERYDAY TOOLS / ONE CLEAR STEP AT A TIME
Circle area
Start with a radius or diameter to find area and circumference.
01 / YOUR NUMBERS↘
Make it your own.
Start with the example below, or enter your values.
⌘ Your inputs stay in this browser.
02 / A LITTLE CLARITYREADY WHEN YOU ARE
Your answer belongs here.
Enter your numbers and we’ll work through the calculation together.
YOUR RESULT
How we got there
GOOD TO KNOW
A few helpful details
How do I use this calculator?
Enter known measurement, measurement value. Choose any available mode, then select Calculate. The example numbers are a starting point you can change.
What if my input cannot be calculated?
A message explains what to change. Previous results are cleared when you edit an input, so the answer always matches the values you calculated.
Are my values sent anywhere?
No. These tools calculate locally in your browser, without an account. Displayed numeric results are rounded; these tools do not provide arbitrary-precision arithmetic.