Area of a Circle Calculator
The area of a circle is π times the radius squared, A = πr²: a circle with a 5 cm radius has an area of 78.5398 cm².
78.5398163397448 cm²
Full answer, then cut to fewer decimals (not rounded):
- 78.5398163397448 cm²
- 78.539816339744 cm²
- 78.53981633974 cm²
- 78.5398163397 cm²
- 78.539816339 cm²
- 78.53981633 cm²
- 78.5398163 cm²
- 78.539816 cm²
- 78.53981 cm²
- 78.5398 cm²
- 78.539 cm²
- 78.53 cm²
- 78.5 cm²
- Area
- 78.5398 cm²
- Radius
- 5 cm
- Diameter
- 10 cm
- Circumference
- 31.4159 cm
In other units: 0.00785398 m² · 7853.98 mm² · 7.85398 × 10⁻⁹ km² · 7.85398 × 10⁻⁷ ha · 0.0845396 ft² · 12.1737 in² · 0.00939328 yd² · 0.00000194076 ac · 3.03244 × 10⁻⁹ mi²
Step-by-step solution
- A = π r²
- A = π × 5² = 78.5398 cm²
Area of a Circle Formula
A = π r² = π d² ÷ 4
r radius, d diameter, π ≈ 3.14159
Worked Example
A circle with a 5 cm radius:
- A = π r²
- A = π × 5² = 78.5398 cm²
Radius: 5 cm · Diameter: 10 cm · Circumference: 31.4159 cm
Same area in other units: 0.00785398 m² · 7853.98 mm² · 7.85398 × 10⁻⁹ km² · 7.85398 × 10⁻⁷ ha · 0.0845396 ft²
Frequently asked questions
How do I find the area of a circle from the diameter?
Halve the diameter to get the radius, then use A = πr², or use A = πd² ÷ 4 directly. A 10 cm diameter gives 78.54 cm².
How do I find the area from the circumference?
r = C ÷ 2π, then A = πr². In one step, A = C² ÷ 4π. A circumference of 31.416 cm gives 78.54 cm².
What is the area of a circle with radius 7 cm?
A = π × 7² = 153.94 cm². With π ≈ 22/7 the textbook answer is 154 cm².
Why is the area of a circle πr²?
Cut a circle into thin wedges and lay them head to tail: they form an approximate rectangle with height r and width πr (half the circumference), so the area is πr × r.
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 Circle Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/area-of-a-circle/
IEEE
Scientific Converters, "Area of a Circle Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/area-of-a-circle/