Circle Calculator
Calculate area, circumference, diameter, and radius of a circle.
Circle Calculator
Calculate area, circumference, diameter, and radius of a circle.
Geometry Formulas
ℹ️ Pythagorean theorem applies only to right-angle triangles. π ≈ 3.14159
Disclaimer
Results provided by this calculator are for informational and educational purposes only. They are based on the values you enter and standard formulas, and should not be considered financial, medical, legal, or professional advice. Always consult a qualified professional before making important decisions based on these results. Roughtools makes no warranties regarding the accuracy or completeness of these calculations for your specific situation.
Frequently Asked Questions
Pro Tips
For percentage calculations, convert the percentage to a decimal first (divide by 100) — this prevents calculation errors: 15% = 0.15, so 15% of 80 = 0.15 × 80 = 12.
When working with large numbers, use scientific notation to check your work. A calculator result that's off by a factor of 10 usually means a decimal point was misplaced.
Standard deviation close to zero means data is clustered tightly around the mean. High SD means high variability. Always report both mean and SD together for complete information.
Cross-check critical calculations with a different method or tool. For geometry, verify with the Pythagorean theorem. For statistics, verify mean with (max+min)/2 as a sanity check.
When to Use This Calculator
Calculate area for flooring, paint coverage, or fencing before purchasing materials.
Verify calculations and practice working through problems step by step.
Calculate room dimensions, wall area, or volume of materials needed for renovation projects.
Quick calculations for engineering problems where precision is needed before formal computation.
Calculate discounts, percentage savings, or unit price comparisons while shopping.
About the Circle Calculator
This circle calculator solves for all four circle measurements — area, circumference, diameter, and radius — when you provide any one of them, using the fundamental relationships between them (A = πr², C = 2πr, d = 2r). Enter any single measurement to instantly see all the others. Works in metric (cm, m) and imperial (in, ft) units. Built for students, engineers, designers, and anyone working with circular shapes.
How to Use the Circle Calculator
- 1
Select which measurement you know: radius, diameter, circumference, or area.
- 2
Enter the known value and select your unit (mm, cm, m, in, ft).
- 3
See all four circle measurements calculated instantly.
- 4
Review the formula used for each calculation.
- 5
Switch between metric and imperial to see unit conversions.
Related Calculators
View all →Area Calculator
Calculate area of rectangle, circle, triangle, and other 2D shapes.
Volume Calculator
Calculate volume of sphere, cube, cylinder, cone, and other 3D shapes.
Surface Area Calculator
Calculate surface area of cube, sphere, cylinder, cone, and other 3D shapes.
Triangle Calculator
Solve any triangle given sides and angles using the law of sines and cosines.
Pythagorean Theorem Calculator
Find the missing side of a right triangle using the Pythagorean theorem.
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