Compute vehicle power-to-weight using horsepower or kilowatts and weight units; see results in hp/ton, kW/ton, W/kg instantly, with examples included.
PWR = Power / Mass
Specific power = P(W) / m(kg) → W/kg
hp/ton = hp / (mass_kg / 1000)
kW/ton = (P(W)/1000) / (mass_kg/1000) = P(W)/m(kg)
Conversions: 1 hp = 745.699872 W; 1 kg = 2.20462262 lb
A Power to Weight Ratio Calculator converts an engine or rider power output and a vehicle (or body) mass into a single performance index. The ratio—power divided by mass—summarizes acceleration potential and climbing ability across cars, motorcycles, bicycles, boats, and aircraft (specific power). Because manufacturers publish power in different units (watts, kilowatts, horsepower) and masses in kilograms or pounds, the calculator standardizes inputs, computes W/kg for technical comparison, and optionally reports popular presentation formats such as hp per metric tonne or hp per short ton. Clear, auditable formulas make it easy to compare trims, evaluate lightweighting, or benchmark training progress in cycling and rowing.
Power-to-weight (specific power) is defined as \(P/m\). For vehicles, higher values generally imply stronger acceleration, especially at lower speeds where aerodynamic drag is smaller. For human power (e.g., cyclists), W/kg is the go-to metric for climbing performance and category benchmarking. The calculator focuses on the necessary inputs—rated power and mass—and then exposes conversions so your results are unit-consistent and comparable. It also prints alternative expressions (hp/tonne, kW/kg) without changing the underlying physics. Keep in mind that real-world performance also depends on gearing, traction, torque curves, drivetrain losses, aero drag, and grade; the ratio is a first-order indicator, not a complete model.
Specific power (SI): \[ \mathrm{PWR}_{\mathrm{W/kg}}=\frac{P_{\mathrm{W}}}{m_{\mathrm{kg}}} = \frac{1000\,P_{\mathrm{kW}}}{m_{\mathrm{kg}}}. \]
Horsepower conversions: \[ P_{\mathrm{W}}=745.7\,P_{\mathrm{hp}},\qquad P_{\mathrm{kW}}=0.7457\,P_{\mathrm{hp}}. \]
Popular displays: \[ \mathrm{hp/tonne}=\frac{P_{\mathrm{hp}}}{m_{\mathrm{kg}}/1000}=\frac{1000\,P_{\mathrm{hp}}}{m_{\mathrm{kg}}},\qquad \mathrm{hp/short\ ton}=\frac{P_{\mathrm{hp}}}{m_{\mathrm{lb}}/2000}=\frac{2000\,P_{\mathrm{hp}}}{m_{\mathrm{lb}}}. \]
From pounds to kilograms: \[ m_{\mathrm{kg}}=\frac{m_{\mathrm{lb}}}{2.20462}. \]
Cycling (W/kg) example form: \[ \mathrm{W/kg}=\frac{P_{\mathrm{FTP}}}{m_{\mathrm{rider+bike}}}. \]
\(P=220\ \mathrm{hp},\ m=1420\ \mathrm{kg}\). \(\mathrm{hp/tonne}=\frac{1000\cdot220}{1420}=155\ \mathrm{hp/t}\). W/kg: \(P_{\mathrm{W}}=220\times745.7=164{,}054\ \mathrm{W}\Rightarrow \mathrm{PWR}=164{,}054/1420=115.5\ \mathrm{W/kg}\).
\(P=110\ \mathrm{hp},\ m=430\ \mathrm{lb}\). \(\mathrm{hp/short\ ton}=\frac{2000\cdot110}{430}\approx512\ \mathrm{hp/ton}\). W/kg: \(m=430/2.20462=195.0\ \mathrm{kg}\Rightarrow \mathrm{PWR}=\frac{110\times745.7}{195.0}=420.7\ \mathrm{W/kg}\).
Rider \(=72\ \mathrm{kg}\), bike \(=8\ \mathrm{kg}\Rightarrow m=80\ \mathrm{kg}\). \(P=320\ \mathrm{W}\Rightarrow \mathrm{W/kg}=320/80=4.0\ \mathrm{W/kg}\).
Around 120–150 W/kg feels lively; 200+ W/kg is rapid. Context (gearing, traction) matters.
hp/ton is familiar to enthusiasts; W/kg is SI and convenient for physics-based comparisons.
Both increase the ratio linearly; the better choice depends on cost, practicality, and class rules.
Torque at the wheels via gearing shapes low-speed response; the ratio is a top-level indicator only.
Use curb (with fluids) plus driver for realistic comparisons; be consistent across vehicles.
No. \(1\ \mathrm{hp}\approx0.7457\ \mathrm{kW}\). Convert before computing ratios.
Climbing speed scales strongly with W/kg; it normalizes performance across different body masses.
Yes, but note EV power delivery and weight distribution; traction limits may dominate.
At higher speeds, aero drag dominates; PWR alone won’t predict top speed.
That measures engine tuning density, not vehicle performance directly; different concept.
They’re standardized but can vary with conditions and dyno method; treat as nominal.