Circle Calculator
Calculate circle measurements from radius, including diameter, circumference, area, sector area, and arc length. Use the angle field for partial-circle examples and the unit tables for conversions.
Input
Radius + Angle
Outputs
5 Circle Values
Use Cases
Geometry, Trig Prep, Layout
Live calculator
Circle measurement inputs
Calculate diameter, circumference, area, sector area, and arc length from radius.
Circle area
78.539816 cm²
Diameter
10 cm
Circumference
31.415927 cm
Sector area
19.634954 cm²
Arc length
7.853982 cm
Circumference in other units
| Unit | Converted value | Meaning |
|---|---|---|
| nm | 314,159,265.359 | Nanometers |
| um | 314,159.2654 | Micrometers |
| mm | 314.1593 | Millimeters |
| cm | 31.4159 | Centimeters |
| dm | 3.1416 | Decimeters |
| m | 0.3142 | Meters |
| dam | 0.0314 | Decameters |
| hm | 0.0031 | Hectometers |
| km | 0.0003 | Kilometers |
| mil | 12,368.475 | Mils |
| in | 12.3685 | Inches |
| ft | 1.0307 | Feet |
| yd | 0.3436 | Yards |
| mi | 0.0002 | Miles |
| nmi | 0.0002 | Nautical miles |
| pt | 890.5302 | Points |
| pc | 74.2109 | Picas |
Area in other units
| Unit | Converted value | Meaning |
|---|---|---|
| nm² | 7,853,981,633,974,483 | Square nanometers |
| um² | 7,853,981,633.9745 | Square micrometers |
| mm² | 7,853.9816 | Square millimeters |
| cm² | 78.5398 | Square centimeters |
| dm² | 0.7854 | Square decimeters |
| m² | 0.0079 | Square meters |
| dam² | 0.0001 | Square decameters |
| hm² | 0 | Square hectometers |
| km² | 0 | Square kilometers |
| mil² | 12,173,695.8801 | Square mils |
| in² | 12.1737 | Square inches |
| ft² | 0.0845 | Square feet |
| yd² | 0.0094 | Square yards |
| mi² | 0 | Square miles |
| nmi² | 0 | Square nautical miles |
| pt² | 63,108.4394 | Square points |
| pc² | 438.2531 | Square picas |
Calculate full-circle and sector measurements
Area and circumference
Find the two most common circle values from a single radius input.
Diameter
Double the radius to get the full width through the circle center.
Sectors and arcs
Use an angle in degrees to calculate partial-circle area and curved edge length.
Circle formulas used on this page
Circle formulas connect radius, diameter, circumference, area, sectors, and arcs through pi.
Working formulas
Diameter
d = 2r
Diameter is twice the radius.
Circumference
C = 2 x pi x r
Circumference is the distance around the circle.
Area
A = pi x r^2
Square the radius before multiplying by pi.
Sector area
sector area = (angle / 360) x pi x r^2
A sector is the same fraction of area as its angle is of 360 degrees.
Symbols
- r - radius
- Distance from the center of the circle to the edge.
- d - diameter
- Distance across the circle through the center.
- C - circumference
- Distance around the outside edge of the circle.
Circle results that keep radius and angle clear
Formula-backed results
- The live calculator appears first so users can enter dimensions before reading long explanations.
- Each result stays connected to a visible formula instead of returning a bare number.
- Inputs accept decimals for measurement problems that do not use whole-number dimensions.
- Copy and print controls help users move results into notes, worksheets, and classroom examples.
Geometry guardrails
- Invalid triangle side sets are labeled clearly before Heron's formula is used.
- Circle calculations use radius consistently so diameter, area, circumference, sectors, and arcs agree.
- Shape labels separate area from perimeter so users do not confuse surface coverage with edge length.
- Related links connect the calculator page to the geometry hub and printable formula reference.
Circle support for geometry and layout
Students
Check homework dimensions while keeping the formula and unit meaning visible.
Teachers
Create quick examples for geometry worksheets, board notes, and answer keys.
Printable work
Print the page with inputs, results, formulas, FAQs, and related geometry links.
How it works in three quick steps.
Enter radius
Use the distance from the center of the circle to its edge.
Enter sector angle
Use degrees from 0 to 360 when calculating a sector or arc.
Read full and partial circle results
Compare diameter, circumference, full area, sector area, and arc length.
Save or print circle calculations
Copy the result
Copy the calculated measurements and formula context into notes or lesson drafts.
Print the page
Print the calculator result with formula explanations and FAQ support below it.
Compare nearby values
Change one dimension at a time to see how the measurement responds.
About this circle calculator
Toolarithm's Circle Calculator is built around radius because radius is the cleanest starting point for the most common circle formulas. From radius, the calculator finds diameter, circumference, area, sector area, and arc length. That lets students compare full-circle and partial-circle measurements without moving between separate tools.
The page separates linear values from square-unit values. Diameter, circumference, and arc length are distances. Area and sector area are surface measurements. That distinction matters in geometry homework, design planning, and worksheet creation because a correct number can still be interpreted incorrectly if the unit type is wrong. The conversion tables keep those meanings visible by showing circumference in length units and area in square units.
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