Circle Conversions
Convert circle measurements — radius, diameter, circumference, area. Free geometry calculators using π.
4 units · 9 conversions
Circle geometry links four key measurements: radius (center to edge), diameter (twice the radius), circumference (perimeter), and area. Given any one, you can derive the others with π.
These are not unit-system conversions — they are geometric relationships. Our tools compute diameter ↔ circumference ↔ area ↔ radius using exact π formulas, with results in consistent length or area units.
Popular circle conversions
Real-world example
You know a pipe outer diameter is 12 cm and need the circumference for a strap clamp. Circumference = π × diameter ≈ 37.7 cm — the minimum strap length before overlap.
All circle conversions
Circle units explained
- Radius (r) · base unit
- Diameter (d)
- Circumference (C)
- Area (A)
Frequently asked questions
- What is the formula for circle circumference?
- Circumference C = 2πr = πd, where r is radius and d is diameter.
- How do I find radius from area?
- Radius r = √(A/π), where A is the circle's area.