Sphere Surface Area Calculator
Enter either the radius or diameter of your sphere. The calculator will compute the total surface area using the formula A = 4πr².
Tip: If both radius and diameter are entered, radius is used first.
What is the area of a sphere?
The area of a sphere (also called surface area) is the total space covering the outside of a perfectly round 3D object. If you could peel the surface like a thin skin and lay it flat, the measurement of that skin is the sphere’s area.
The standard formula is:
A = 4πr²
where A is the surface area and r is the radius.
How to use this calculator
- Enter the radius directly, or enter the diameter instead.
- Add a unit label if you want output like cm², m², or in².
- Click Calculate Area to get the exact value in terms of π and the decimal approximation.
- Use Reset to clear all fields and start over.
Sphere area formula explained
Using radius
When radius is known, square it and multiply by 4π:
A = 4πr²
Using diameter
If diameter is given, convert to radius first:
r = d / 2.
Then apply:
A = 4π(d/2)² = πd².
Worked examples
Example 1: Radius = 3 cm
A = 4π(3²) = 4π(9) = 36π ≈ 113.10 cm²
Example 2: Diameter = 12 m
Radius is 12 / 2 = 6 m, so:
A = 4π(6²) = 4π(36) = 144π ≈ 452.39 m²
Common mistakes to avoid
- Using diameter directly in
4πr²without dividing by 2 first. - Forgetting to square the radius.
- Mixing units (for example, radius in cm and answer in m²).
- Confusing sphere surface area with sphere volume.
Quick reference
- Surface area:
4πr² - Volume:
(4/3)πr³ - Great-circle circumference:
2πr
Whether you are solving geometry homework, engineering dimensions, or estimating material coverage, this sphere surface area calculator gives a fast and accurate result.