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Engine Horsepower Calculator

Use this Engine Horsepower Calculator to convert torque and RPM into horsepower (HP) and kilowatts (kW). Enter your torque value, select its unit, add engine speed (RPM), and press Calculate.

Formula: HP = (Torque in lb-ft × RPM) ÷ 5252. If torque is entered in N·m, the calculator converts it to lb-ft automatically.

Tip: For best accuracy, use torque measured at the engine (crank) and the RPM at which that torque applies.

The Engine Horsepower Calculator makes it fast and simple to convert engine torque and RPM into horsepower (HP) and kilowatts (kW). Whether you are tuning a street car, analyzing dyno data, or comparing engine specs, this tool turns raw numbers into clear power figures you can trust.

What is engine horsepower?

Horsepower is a measure of how quickly an engine can do work. In practical terms, it tells you how strongly and how quickly an engine can deliver torque across the rev range. The relationship between torque and horsepower is governed by a simple and widely accepted formula: horsepower equals torque (in lb-ft) multiplied by RPM, divided by 5252. Because torque and RPM constantly change as an engine revs, peak horsepower is typically reported at the engine speed where that product is highest.

How the Engine Horsepower Calculator works

This calculator uses the classic formula for mechanical horsepower:

  • HP = (Torque in lb-ft × RPM) ÷ 5252
  • If you enter torque in N·m, the calculator converts N·m to lb-ft (1 N·m ? 0.737562149 lb-ft) before applying the formula.
  • It also converts the result to kilowatts using 1 HP ? 0.745699872 kW, giving you both HP and kW at once.

Why 5252?

The number 5252 is a constant derived from unit conversions that link rotational speed (RPM), torque (lb-ft), and horsepower. It represents the point on a power curve where torque and horsepower values are numerically equal (at 5252 RPM) when measured in lb-ft and HP.

How to use the Engine Horsepower Calculator

  1. Enter the torque value measured for your engine. You can use either lb-ft or N·m.
  2. Select the correct torque unit to ensure accurate conversion.
  3. Enter the engine speed (RPM) at which the torque value applies.
  4. Click Calculate to get horsepower (HP) and kilowatts (kW) instantly.

When should you use this calculator?

Use the calculator any time you have torque and RPM data and want power. Common scenarios include:

  • Reviewing dyno sheets that list torque at specific RPM points.
  • Estimating power after changes such as intake, exhaust, tune, or boost adjustments.
  • Comparing engines that publish torque figures but not horsepower.
  • Converting between imperial and metric power units for international specs.

Tips for accurate results

  • Use torque measured at the crankshaft (engine) rather than at the wheels to avoid drivetrain loss effects.
  • Match torque and RPM from the same operating point. Mixing peak torque at one RPM with a different RPM will produce incorrect horsepower.
  • If your torque is in N·m, ensure the unit selector is set to N·m so the conversion is applied correctly.
  • Remember that environmental conditions (temperature, altitude, humidity) can influence measured torque; standardized correction factors may apply on professional dynos.

Understanding the outputs

The calculator returns two power values:

  • Horsepower (HP) — mechanical horsepower commonly used in the U.S. and many performance contexts.
  • Kilowatts (kW) — the SI power unit, helpful for technical comparisons and international specs.

Example calculation

Suppose your engine produces 300 lb-ft at 5,500 RPM. Horsepower is (300 × 5,500) ÷ 5252 ? 314.4 HP, which is about 234.5 kW. If your torque value were 406 N·m at the same RPM, the calculator would first convert 406 N·m to about 300 lb-ft, then produce the same horsepower figure.

Engine horsepower vs. wheel horsepower

This tool focuses on engine (crank) horsepower computed from torque and engine speed. Wheel horsepower (WHP) measured on a chassis dyno is typically lower due to drivetrain losses. While this calculator does not apply drivetrain loss percentages, you can estimate engine horsepower from wheel horsepower by dividing by (1 ? loss). For example, with an estimated 15% loss, engine HP ? WHP ÷ 0.85.

Why this calculator is reliable

The formula used is industry-standard and based on fundamental physics and unit conversions. By converting torque to the correct unit and applying the precise constants for HP and kW, the Engine Horsepower Calculator provides consistent and transparent results you can verify by hand.

FAQs

How does the Engine Horsepower Calculator convert torque and RPM to horsepower?

It applies HP = (Torque in lb-ft × RPM) ÷ 5252, converting N·m to lb-ft when needed.

What units does the Engine Horsepower Calculator support?

You can enter torque in lb-ft or N·m; the calculator outputs power in HP and kW.

Is the Engine Horsepower Calculator accurate for any RPM?

Yes, as long as the torque value you enter corresponds to that specific RPM.

Can the Engine Horsepower Calculator estimate kilowatts?

Yes. It converts HP to kW using 1 HP ? 0.745699872 kW.

Do I need crank or wheel torque for the Engine Horsepower Calculator?

Use crank (engine) torque for engine HP. Wheel torque includes drivetrain losses.

Why does the Engine Horsepower Calculator use 5252 in the formula?

5252 is the conversion constant linking lb-ft, RPM, and mechanical horsepower.

Can I use metric torque with the Engine Horsepower Calculator?

Absolutely. Enter N·m and the tool converts to lb-ft automatically before calculating.

Will the Engine Horsepower Calculator work with decimal torque values?

Yes, it accepts decimal inputs and returns results to two decimal places.