Power density is the amount of power (time rate of energy transfer) per unit volume.^[1]It is typically measured in watts per cubic meter (W/m³) and represents how much power is distributed within a given space. In various fields such as physics, engineering, and electronics, power density is used to evaluate the efficiency and performance of devices, systems, or materials by considering how much power they can handle or generate relative to their size or volume.^[2]

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In energy transformers including batteries, fuel cells, motors, power supply units, etc., power density refers to a volume, where it is often called volume power density, expressed as W/m³.

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

• Surface power density, energy per unit of area
• 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)