RightSizeTools Practical sizing calculators
Geometry Basics

Circle Area & Circumference Calculator

Enter a circle radius to calculate area and circumference. For a round patio, pad, tank, or table, use half the diameter as the radius.

Last updated: May 2026

Unit system Switch between U.S. customary and metric units. Your choice is remembered on other calculators.

Circle measurement

Radius is the distance from the center of the circle to the outside edge. Diameter is twice the radius.

Visual guide

Which measurement goes where?

Radius goes from the center to the edge. Diameter goes all the way across the circle and equals two radii.

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Buying and sizing notes

How to use this estimate

What this includes

  • The required inputs shown on this page
  • common planning assumptions
  • optional advanced adjustments where provided

What it does not include

  • site-specific professional design
  • local code approval
  • manufacturer-specific requirements
  • installation quality

Common mistakes

  • Leaving a required input at the default when your situation is different
  • ignoring product labels or ratings
  • treating the estimate as an exact final answer

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