Calculator for circle

Formula

Area = π × radius². Circumference = 2 × π × radius. Diameter = 2 × radius. π dey used at full precision and results dey rounded to two decimals for display.

Example wey show the calculation

Radius 5: area = π × 5² = π × 25 = 78.54. Circumference = 2 × π × 5 = 31.42. Diameter = 10. If radius be 5 cm, area na 78.54 cm² and circumference na 31.42 cm.

Where e fit work and limits

This na perfect circle: one radius, one centre. Ellipses, arcs, sectors, and rings need their own formulas and dem no cover am here. Page no dey convert units — radius in inches dey give area in square inches; convert first if you need another unit.

Version of di formula: 026488602e53 · Example don get check: 2026-10-31

Questions wey people dey ask often

Make I enter radius abi diameter?

Radius: distance from centre to edge. If you only know diameter (edge to edge through centre), halve am first — or read diameter chip above in reverse.

Why area dey use square units?

Because area dey cover surface. Radius of 5 cm dey give 78.54 cm², no be 78.54 cm. Mixing the two na most common circle mistake.

Which value of pi this tool dey use?

Full double-precision pi (3.141592653589793…), no be 3.14. Difference only matter pass second decimal, but no reason to round early.

How area dey grow as radius increase?

Area dey grow with the square of radius. Circle wey get radius 10 get area 314.16, exactly four times the area 78.54 for circle wey get radius 5.

I fit use am for sphere?

No. Sphere surface area na 4πr² and volume na (4/3)πr³ — different formulas for 3D object.

Wetin if na circumference I know?

Divide am by 2π to get radius, then enter am here. For circumference of 31.42, radius na 31.42 ÷ 6.2832 = 5.

Other tools wey relate to dis

• Calculator for square area — the same idea for square plot
• Converter for area units — square metres, square feet, acres and other units
• Converter for volume units — when work move from flat area to 3D capacity