Power density

This article is about power per volume. For power per unit mass, see power-to-weight ratio. For power per area, see surface power density.

Power density
SI unit	W/m3
In SI base units	kg·m−1s−3
Derivations from other quantities	P/V

Power density (or volume power density or volume specific power) is the amount of power (time rate of energy transfer) per unit volume.

In energy transformers including batteries, fuel cells, motors, etc., and also power supply units or similar, power density refers to a volume. It is then also called volume power density, which is expressed as W/m³.

Volume power density is sometimes an important consideration where space is constrained.

In reciprocating internal combustion engines, power density—power per swept volume or brake horsepower per cubic centimeter —is an important metric. This is based on the internal capacity of the engine, not its external size.

Power densities of common materials

Storage material	Energy type	Specific power (W/kg)	Power density (W/m3)
Hydrogen (in star)	Stellar fusion	0.00184	276.5
Plutonium	Alpha decay	1.94	38,360

See also

• Energy density, energy per unit volume
• Specific energy, energy per unit mass
• Power-to-weight ratio/specific power, power per unit mass
  • Specific absorption rate (SAR)