Circle Dimension Hub — Circumference, Diameter, Radius & Area Calculator
Enter any one of circumference (C), diameter (D), radius (r), or area (A) — the other three are computed automatically, with a diagram.
Worked Calculations (verified)
Example 1: Circle circumference 31.416 cm
| Circumference (C) | 31.416 cm |
| Diameter (D) | 10.000023 cm |
| Radius (r) | 5.0000117 cm |
| Area (A) | 78.540184 cm² |
Example 2: Circle diameter 14 cm
| Circumference (C) | 43.982297 cm |
| Diameter (D) | 14 cm |
| Radius (r) | 7 cm |
| Area (A) | 153.93804 cm² |
Example 3: Circle radius 10 cm
| Circumference (C) | 62.831853 cm |
| Diameter (D) | 20 cm |
| Radius (r) | 10 cm |
| Area (A) | 314.15927 cm² |
Example 4: Circle area 314.1593 cm²
| Circumference (C) | 62.831857 cm |
| Diameter (D) | 20.000001 cm |
| Radius (r) | 10.000001 cm |
| Area (A) | 314.1593 cm² |
Frequently Asked Questions (FAQ)
How do I find the radius from a circle’s circumference?
Divide the circumference by 2π: r = C ÷ (2 × 3.14159…). Example: circumference 31.416 cm → r = 31.416 ÷ 6.28319 ≈ 5.00001 cm, effectively 5 cm. The calculator above computes it automatically — select the “Circumference” mode and enter the number.
What is the formula for converting circumference to diameter?
D = C ÷ π. Since circumference = π × diameter, diameter = circumference divided by π (≈ 3.14159). Example: C = 31.416 cm → D ≈ 10 cm.
How do I calculate a circle’s area if I know its circumference?
Use A = C² ÷ (4π). Example: C = 31.416 cm → A = 31.416² ÷ 12.56637 ≈ 78.5402 cm². This tool shows the area automatically from any circumference input.
How do I find the circumference from a circle’s area?
C = 2 × √(π × A). Example: A = 314.1593 cm² → C = 2 × √(986.96…) ≈ 62.8319 cm. Select the “Area” mode on the calculator for this conversion.
How is this tool different from convert-diameter-to-circumference-calculator?
The legacy convert-diameter-to-circumference-calculator tool is one-way only: diameter → circumference. This tool is an all-pairs circle dimension hub: input ANY ONE of circumference, diameter, radius, or area, and the other three are computed at once, with a diagram.
Which units are supported?
Millimeters (mm), centimeters (cm), meters (m), inches (in), and feet (ft). Area automatically follows the squared unit (e.g. cm → cm²). Conversions use exact factors, e.g. 1 inch = 2.54 cm.
How precise are the results?
The engine uses 64-bit floating point (±15–16 significant digits) and full π, then results are displayed with at most 8 significant digits. For C = 31.416, r ≈ 5.00001 — 0.0002% off the round number 5.
When should I use diameter vs radius?
Radius is used in the area formula (A = πr²) and in physics/engineering; diameter is more common in product specs (pipes, wheels, pans). They are interchangeable — D = 2r — and this hub shows both at once.
Related Tools
- convert-diameter-to-circumference-calculator — one-way diameter → circumference converter (legacy).
- circle-area — circle area calculator from radius.
- how-to-find-the-diameter-of-a-circle — guide to finding the diameter.
Scope note: this tool is an all-pairs circle dimension hub (full two-way C/D/r/A). The legacy tools above remain available for specific one-way needs.
Free tool by NRTechStudio