horsepowertoweight

Horsepower-to-weight, also called power-to-weight ratio, is a measure of an engine’s or vehicle’s power output relative to its mass. It is commonly used to estimate performance, particularly acceleration, by comparing how much power is available per unit of weight.

Calculation and units: The ratio is typically expressed as horsepower per tonne (hp/ton) or kilowatts per tonne (kW/tonne). Power can be in horsepower (hp) or kilowatts (kW), and weight in metric tonnes or kilograms. 1 hp is about 0.7457 kW, and 1 tonne equals 1000 kg. For example, a car with 250 hp and a curb weight of 1500 kg (1.5 tonnes) has about 167 hp/ton and about 124 kW/tonne (186.4 kW / 1.5 t).

Use and interpretation: A higher power-to-weight value generally indicates stronger acceleration, given similar drivetrain efficiency and aerodynamics. It is a useful rough comparator among vehicles. However, power-to-weight does not capture all factors that affect performance, such as torque characteristics, gearing, traction, tire grip, aerodynamics, and drag.

Typical ranges: In passenger cars, power-to-weight often falls roughly between 50 and 150 hp/ton, with sports cars typically higher and heavy trucks lower. Performance enthusiasts may seek higher values, but real-world behavior depends on the entire propulsion and handling system.

Limitations and considerations: The metric depends on how power is measured (engine horsepower gross vs. net) and what weight is used (curb, dry, or operating weight). It does not reflect drivetrain losses, weight distribution, or dynamic efficiency under different speeds and loads.