Horsepower Calculator

This professional-grade horsepower calculator helps engineers, tuners, and enthusiasts compute engine power using multiple methods: torque and RPM, quarter-mile trap speed, or elapsed time (ET). It supports metric and imperial units, provides optional drivetrain-loss adjustments, and is accessible and mobile-first.

Interactive Calculator

Choose calculation method

Used to derive estimated wheel horsepower from crank horsepower.

Results

Values update as you type. All outputs are rounded to two decimals for readability.

Crank Horsepower (hp) 0.00 hp
Power (kW) 0.00 kW
Estimated Wheel Horsepower (whp) —
Power-to-Weight —

Data Source and Methodology

Primary standard: SAE International, “SAE J1349 – Engine Power Test Code,” Rev. J1349_201106, 2011. Link: https://www.sae.org/standards/content/j1349_201106/

Unit definitions and constants: NIST Special Publication 811, “Guide for the Use of the International System of Units (SI),” 2008 Edition, updated 2018. Link: https://www.nist.gov/pml/special-publication-811

Empirical drag racing estimates: Patrick Hale, Quarter-Mile performance heuristics (commonly expressed as HP = W × (mph/234)^3 and HP = W / (ET/5.825)^3), widely referenced across motorsports literature.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

1) Torque and RPM to horsepower (imperial):

\( \mathrm{HP} \;=\; \dfrac{T_{\mathrm{lb\cdot ft}} \times \mathrm{RPM}}{5252} \)

2) Torque and RPM to horsepower (SI, direct to mechanical hp):

\( \mathrm{HP} \;\approx\; \dfrac{T_{\mathrm{N\cdot m}} \times \mathrm{RPM}}{7127} \)

3) Torque and RPM to kilowatts (SI):

\( \mathrm{kW} \;=\; \dfrac{T_{\mathrm{N\cdot m}} \times \mathrm{RPM}}{9549} \)

4) Trap speed estimate (crank horsepower):

\( \mathrm{HP} \;=\; W_{\mathrm{lb}} \left(\dfrac{V_{\mathrm{mph}}}{234}\right)^{3} \)

5) ET estimate (crank horsepower):

\( \mathrm{HP} \;=\; \dfrac{W_{\mathrm{lb}}}{\left(\dfrac{\mathrm{ET}}{5.825}\right)^3} \)

6) Wheel horsepower given drivetrain loss fraction \( \lambda \):

\( \mathrm{whp} \;=\; \mathrm{HP} \times (1 - \lambda) \)

Glossary of Variables

How it Works: A Step-by-Step Example

Scenario: You measured 320 N·m at 6,000 rpm. You want crank hp, kW, and an estimate of wheel hp for a RWD car (≈15% loss).

  1. Select “Torque & RPM”. Enter T = 320 N·m, RPM = 6000.
  2. Compute hp using SI form: \( \mathrm{HP} = \dfrac{320 \times 6000}{7127} \approx 269.3 \) hp.
  3. Compute kW: \( \mathrm{kW} = \dfrac{320 \times 6000}{9549} \approx 201.0 \) kW.
  4. Apply drivetrain loss λ = 0.15: whp = 269.3 × (1 − 0.15) ≈ 229.9 whp.

The calculator performs these steps automatically, including precise unit conversions.

Frequently Asked Questions (FAQ)

Is the 5252 constant exact?

Yes. 5252 results from 33,000 ft·lbf/min per hp divided by 2π rad/rev, with unit conversions. It is exact in the imperial definition.

Are the ET and trap-speed formulas crank or wheel horsepower?

They estimate crank horsepower under typical conditions. Use the drivetrain-loss control to estimate wheel horsepower.

Which weight should I enter?

Use race weight including driver and fuel. If you only know curb weight, add driver and fuel to improve accuracy.

Why do my dyno numbers differ from these estimates?

Dynos vary by type and correction standard (SAE vs. STD), tire temperature, strapping, and airflow. Trap-speed/ET methods also assume typical aero and gearing.

Can I use km/h and kg?

Yes. Select the appropriate units. Conversions use precise factors: 1 kg = 2.2046226218 lb; 1 mph = 1.609344 km/h.

Do you support metric horsepower (PS)?

This tool reports mechanical horsepower (hp) and kilowatts. To approximate PS, multiply kW by 1.35962.

Strumento sviluppato da Ugo Candido,. Contenuti verificati da,.
Ultima revisione per l'accuratezza in data: .