Radius Calculator: Fast Circle Measurements from One Value

Your Go-To Tool for Circle Measurements

Need a quick way to find a circle radius? This radius calculator gives clear results from one input.

Pick diameter, circumference, or area using simple radio options. One input field keeps the process clear and fast.

Enter a number and press Calculate. You get radius, diameter, circumference, and area.

The layout now uses one field with a radio choice. This update cuts errors and speeds up entry.

How It Works

The radius calculator uses standard circle formulas with pi. Pi equals about 3.14159. Results display with four decimal places.

• From diameter: r = d ÷ 2
• From circumference: r = C ÷ 2π
• From area: r = √(A ÷ π)
• Then it computes diameter = 2r, circumference = 2πr, and area = πr²

How to Use This Tool

1. Pick what you will enter: diameter, circumference, or area.
2. Type a positive number in the input field.
3. Check the unit label near the field.
4. Press Calculate to get results.
5. Press Enter to run the calculation.
6. Press Clear to reset and switch back to diameter.

Input and Output Guide

Inputs

• Radio choice sets what the number means.
• The field accepts whole numbers and decimals.
• The label shows units or square units based on your choice.
• Use any unit you like, such as centimeters or inches.
• Use one unit across all values for clean results.

Outputs

• Radius shows in units.
• Diameter shows in units.
• Circumference shows in units.
• Area shows in square units.
• A note states which input you used and its value.
• Each value displays to four decimal places.

Notes and Limits

• Enter positive numbers only.
• The tool keeps your unit the same across results.
• No unit conversion appears in the display labels.
• Pi comes from the built in math constant.
• Very large values may show small rounding shifts.
• We apply the utmost care to formulas and rounding.

Examples and Use Cases

Examples

• Enter diameter 10 units. Radius 5.0000 units. Circumference 31.4159 units. Area 78.5398 square units.
• Enter circumference 50 units. Radius 7.9577 units. Diameter 15.9155 units. Area 198.9437 square units.
• Enter area 200 square units. Radius 7.9788 units. Diameter 15.9577 units. Circumference 50.1327 units.

Common use cases

• Homework checks for geometry and trigonometry.
• Woodworking for round tabletops and trays.
• Pipe, tube, and gasket sizing for projects.
• 3D prints that need precise circular parts.
• Graphic design for rings, badges, and logos.

This radius calculator saves time on every use. Each project has unique unit needs, and this tool fits them all.

Pick one value, enter the number, and get everything you need.