Circle Diameter from Radius, Area or Circumference
Find circle diameter and radius from one known measurement.
Formula
d=2r=C/π=2√(A/π).
Radius or circumference: 5 cm · Area: 25 cm² · Diameter ≈ 200×(5 cm × 0.01 m/cm) · Radius ≈ 100×(5 cm × 0.01 m/cm)
How to use
- Choose the known measurement.
- Enter length or area; leave the unused field unchanged.
- Read diameter and radius in cm.
Examples
- Area 25π cm² gives diameter 10 cm.
Frequently asked questions
Which length should I enter?
Use radius or circumference, according to the selected mode.
Can I enter area?
Yes. Select area and use the area field with square units.
Are negative inputs valid?
No. Circle measurements must be positive.
Sources
Updated: