Distinguish short tons and metric tonnes
A US short ton is 2,000 lb; a metric tonne is 1,000 kg. Mechanical horsepower also differs from metric horsepower. Use consistent engine or wheel power, and compare vehicles in equivalent load states. The inverse, pounds per horsepower, improves as the numeric value falls, while power per tonne improves as it rises.
lb/hp = weight_lb/HP; hp/US short ton = HP × 2,000/weight_lbFollow the worked comparison below for the input units and assumptions.
Work through an example
400 mechanical hp and 3,200 lb give 250 hp per US short ton and 8 lb/hp. The corresponding metric value is approximately 205.50 kW per tonne. Adding passenger or equipment weight reduces the ratio without changing engine power.
State whether the figure is power per mass or mass per power
Higher horsepower per ton means more power for the same mass. Lower pounds per horsepower expresses the same improvement in inverse form. Avoid comparing the raw numbers across these two conventions or across short tons and metric tonnes.
Use the same load and measurement basis
Compare both vehicles with driver and equivalent fuel or equipment load, and use the same definition of power. Adding mass lowers power-to-weight even if engine output is unchanged. A wheel-power figure and an engine-power rating describe different measurement locations.
Compare power-to-weight with consistent load states
Hold mechanical horsepower at 400 and vary race-ready weight. Higher hp per short ton and lower pounds per horsepower describe the same directional improvement. The table uses US short tons, not metric tonnes.
lb/hp = weight_lb/HP; hp/US short ton = HP × 2,000/weight_lb- Identify whether the power value is an engine rating, a measured engine output or measured wheel power.
- Use comparable load states, including driver and appropriate fuel or equipment.
- Choose a consistent unit convention and label both numerator and denominator.
- Interpret the ratio alongside traction, gearing and power delivery rather than converting it directly into a promised acceleration time.
| Race-ready weight (lb) | Mechanical hp | lb/hp | hp/US short ton |
|---|---|---|---|
| 2800 | 400 | 7 | 285.71 |
| 3200 | 400 | 8 | 250 |
| 3600 | 400 | 9 | 222.22 |
Adding 400 lb to the 3,200 lb case worsens the ratio from 8 to 9 lb/hp without changing engine power. The inverse measure falls from 250 to about 222.22 hp per US short ton. Keep the convention visible so a larger number is not mistakenly described as better in both columns.
Check the inputs before interpreting a difference
Do not compare mechanical hp per short ton directly with kW per metric tonne as if the numeric scales matched. A measured wheel-power input and a published engine rating also need a consistent measurement basis before drawing conclusions.
Before you apply the result
The ratio alone does not predict 0–60 time. Our 0–60 worksheet instead uses an entered average acceleration and assumes constant acceleration for distance. Traction, drag, gearing and power delivery remain outside that simple model.
Try the calculation
Enter your own values in the related calculators. Compare one input at a time and keep units and operating conditions visible with the result.
Frequently asked questions
Is hp per ton the same as hp per tonne?
No. A US short ton is 2,000 pounds; a metric tonne is 1,000 kilograms. Label which denominator you use.
Is lower pounds per horsepower better?
It represents more power per unit mass, assuming comparable power measurements and load states.
Can power-to-weight predict 0–60 time?
Not by itself. Traction, gearing, resistance and power delivery affect acceleration. The separate worksheet uses an entered average acceleration.
How does adding a passenger affect power-to-weight?
Add the passenger and equipment to total mass while holding power unchanged. Power per unit mass falls, while mass per unit power rises. This alone does not determine the exact change in acceleration time.
Reference and method
Power and rate of work; mechanical horsepower conversion follows 550 ft·lbf/s.
NASA Glenn — What is power? ↗These explanations and examples describe the documented model. No manufacturer testing, named expert authorship or independent professional review is claimed. Read the method policy or report a correction.