# Annulus Area Calculator (Ring)

URL: https://speedycalculator.com/calculators/math/annulus/
Last updated: 2026-10-25

> The annulus calculator finds the area of a ring between two concentric circles from the outer and inner radii. Use it for washers, pipes, running tracks and circular paths.

## Inputs

- Outer radius (m, cm, mm, km, in, ft, yd, mi)
- Inner radius (m, cm, mm, km, in, ft, yd, mi)

## Results

- Ring area
- Ring width

## Formula

```
Area = π(R² − r²)
```

## Explanation

An annulus is the flat ring shape left when a smaller circle is cut from the centre of a larger one.

### How to use the Annulus Area Calculator

- **Outer radius**
- **Inner radius**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Subtract the inner circle’s area from the outer circle’s area.

### Inputs explained

FieldWhat to enterOuter radiusUnits: m, cm, mm, km, in, ft …Inner radiusUnits: m, cm, mm, km, in, ft …

### What each result means

- **Ring area** = pi×([Outer radius]^2 - [Inner radius]^2)
- **Ring width** = [Outer radius] - [Inner radius]

### Example values

How the main result changes when **Outer radius** changes and everything else stays at the example values above:

Outer radius (m)Ring area (m²)5-75.47.522.7810160.2212.5336.9415552.92201,102.7

## Worked example

Inputs — Outer radius: 10 m; Inner radius: 7 m.

Results — **Ring area = 160.22 m²**; Ring width = 3 m.

## FAQ

**Can I use diameters?**
Halve them first to get radii.

**What if the inner radius is larger?**
Swap them; the outer radius must be bigger.

**What formula does the Annulus Area Calculator use?**
Area = π(R² − r²).