Annulus (Ring) Area
Subtract the inner circle’s area from the outer circle’s. The extra figures are the ring’s width and the circumference at its mid-radius.
Your numbers
Area
201.062cm²
Side length
4cm
Circumference
50.265cm
Formula
Area = π × (Radius² − Inner radius²)
Use it for washers, pipe cross-sections and the border of a circular bed.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Radius (cm)Centre to edge — half the diameter. | 10 | 0 and up |
| Inner radius (cm)The smaller of two radii when the ends differ. | 6 | 0 and up |
Step by step
Quick reference table
Results when only Radius (cm) changes and everything else stays put.
| Radius (cm) | Area (cm²) | Side length (cm) | Circumference (cm) |
|---|---|---|---|
| 5 | 0 | 0 | 34.558 |
| 7.5 | 63.617 | 1.5 | 42.412 |
| 10 | 201.062 | 4 | 50.265 |
| 15 | 593.761 | 9 | 65.973 |
| 20 | 1,143.54 | 14 | 81.681 |
What each result means
| Result | At default values |
|---|---|
| Area (cm²)The space a shape covers — length squared. | 201.062 |
| Side length (cm)One side of a regular polygon — they are all the same. | 4 |
| Circumference (cm)The distance once around a circle. | 50.265 |
Common mistakes
Use it for washers, pipe cross-sections and the border of a circular bed.
Glossary
- Radius
- Centre to edge — half the diameter.
- Inner radius
- The smaller of two radii when the ends differ.
- Area
- The space a shape covers — length squared.
- Side length
- One side of a regular polygon — they are all the same.
- Circumference
- The distance once around a circle.
Frequently asked questions
Q. How is Annulus (Ring) Area calculated?
Area = π × (Radius² − Inner radius²) — Subtract the inner circle’s area from the outer circle’s. The extra figures are the ring’s width and the circumference at its mid-radius.
Q. Can you walk through an example?
With Radius 10cm, Inner radius 6cm, the answer is Area 201.062cm².
Q. What do I need to enter?
Enter Radius, Inner radius. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Radius (cm) moves the answer to Radius (cm) 5 → Area (cm²) 0 and Radius (cm) 20 → Area (cm²) 1,143.54. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Use it for washers, pipe cross-sections and the border of a circular bed.
Related calculators
Keep your length units consistent across inputs — mixing centimetres and metres throws results far off.