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Library / Foundations: Maths / FMA-11

Foundations: Maths

Sphere: volume and surface area

Volume of a sphere from its radius.

Ref
FMA-11
Rev
v1
Field
Foundations: Maths
Result
V [cm³]

r is the radius, half the diameter. Volume is in cubic units and surface area in square units.

The volume of a sphere grows with the cube of its radius: double the radius and the volume is eight times larger.

Calculator

Solve for
cm³
cm
0.550
  • Surface area 4πr²314.2 cm²
  • Volume in litres0.5236 L

What drives the result

Each variable is moved across its typical range while the others stay at the values above. The longest bar is the key driver.

Volume (cm³) current value 523.6 cm³
rRadiusKey driver
0.524524,000
  • Volume goes as r³ and surface area as r², so large spheres have less surface per unit volume.
  • Use the radius, not the diameter.
Chart data as tables

Ranked variables

VariableTypical rangeLowest resultHighest resultSwing (cm³)Local stepChange in result
r Radius0.5 to 50 cm0.5236523,600523,600+10%+33.1 %

Sweep of Radius

Radius (cm)Volume (cm³)
0.50.5236
0.88912.944
1.58116.56
2.81293.11
5523.6
8.8912,944
15.8116,560
28.1293,110
50523,600

Sweep one variable

Volume (cm³)Hover, touch, or use the arrow keys on the chart
0100k200k300k400k500k 0.5125102050 Radius (cm), log scale now 523.6

Variables and how each one contributes

V

Volume

Result · cm³

What the equation gives you. Everything else feeds it.

r

Radius

cm · typical 0.5 to 50

Distance from the centre to the surface. Cubed: +10% radius gives +33% volume.

Worked example with the values above

  1. Cube the radius: 5³ = 125.
  2. Multiply by 4π/3 ≈ 4.18879.
  3. V = 523.6 cm³.

Assumptions and limits

  • A perfect sphere.
  • Radius in the same unit as the volume.

Common mistakes

  • Using the diameter.
  • Squaring instead of cubing.

Statistics and uncertainty

The cube amplifies errors by three: δV/V = 3δr/r. A 1% error in diameter gives a 3% error in volume.

Where it is used

  • Tank and balloon volumes.
  • Mass of spherical shot from density.

Maths you need

  • Cubes: r³
  • Pi: ≈ 3.14159

Related formulas

Practise this formula