Area of a Ring (Annulus) Calculator
The area of a ring is the difference between two circles, A = π(R² − r²): R = 10 cm and r = 6 cm give 201.062 cm².
201.061929829747 cm²
Full answer, then cut to fewer decimals (not rounded):
- 201.061929829747 cm²
- 201.06192982974 cm²
- 201.0619298297 cm²
- 201.061929829 cm²
- 201.06192982 cm²
- 201.0619298 cm²
- 201.061929 cm²
- 201.06192 cm²
- 201.0619 cm²
- 201.061 cm²
- 201.06 cm²
- 201.0 cm²
- Area
- 201.062 cm²
- Ring width
- 4 cm
In other units: 0.0201062 m² · 20106.2 mm² · 2.01062 × 10⁻⁸ km² · 0.00000201062 ha · 0.216421 ft² · 31.1647 in² · 0.0240468 yd² · 0.00000496835 ac · 7.76304 × 10⁻⁹ mi²
Step-by-step solution
- A = π (R² − r²)
- A = π × (10² − 6²) = 201.062 cm²
Area of a Ring (Annulus) Formula
A = π (R² − r²)
R outer radius, r inner radius
Worked Example
A ring with outer radius 10 cm and inner radius 6 cm:
- A = π (R² − r²)
- A = π × (10² − 6²) = 201.062 cm²
Ring width: 4 cm
Same area in other units: 0.0201062 m² · 20106.2 mm² · 2.01062 × 10⁻⁸ km² · 0.00000201062 ha · 0.216421 ft²
Frequently asked questions
How do I find the area of a ring from its thickness?
With outer radius R and thickness t, r = R − t, so A = π(2Rt − t²). For a thin ring this is about 2πRt, the circumference times the thickness.
How do I find the cross-sectional area of a pipe wall?
Use diameters: A = π(D² − d²) ÷ 4 with outside diameter D and inside diameter d. The tensile stress calculator uses the same formula for round tubes.
What is an annulus?
The region between two concentric circles, such as a washer, a pipe cross-section or a running track.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
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APA
Scientific Converters. (2026, October 15). Area of a Ring (Annulus) Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/area-of-a-ring/
IEEE
Scientific Converters, "Area of a Ring (Annulus) Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/area-of-a-ring/