Horsepower Calculator

Horsepower Is Torque Multiplied by How Fast It Spins

Torque tells you how hard an engine twists; horsepower tells you how much work it can do per unit time, which is why two engines with identical peak torque can feel completely different if one makes it at 2,500 RPM and the other at 6,500 RPM. This calculator covers both the standard dyno-style calculation from torque and RPM, and a separate quarter-mile trap-speed method that estimates horsepower from performance data alone.

The Formula

The constant 5252 is not arbitrary — it's the RPM at which torque in lb-ft and horsepower are numerically equal, a direct consequence of the unit conversion between rotational work and power.

Where This Matters

• Reading a dyno sheet — dyno software reports raw torque and RPM curves; converting to horsepower at each point shows exactly where an engine's power peaks.
• Comparing engines with different powerbands — a high-revving small-displacement engine and a low-revving large-displacement engine can produce the same peak horsepower through very different torque-RPM combinations.
• Estimating power from a quarter-mile time slip — the trap-speed formula gives a rough horsepower estimate using only weight and trap speed, useful when no dyno data exists.
• Modification planning — knowing at what RPM peak torque and peak horsepower occur helps choose gearing that keeps the engine in its most effective range.

Horsepower at Various RPM, 300 lb-ft Constant Torque

Computed directly from HP = (Torque × RPM) ÷ 5252 at a constant 300 lb-ft.

How to Use This Calculator

1. Choose calculation mode: From Torque & RPM, or From Weight & Quarter-Mile Trap Speed.
2. Select Imperial or Metric units for the chosen mode.
3. Enter torque and RPM (or vehicle weight and trap speed).
4. Select Calculate to see the estimated horsepower.

Related Calculations

Need the reverse calculation? Use the Torque Calculator, or check crank-measured output specifically with the Brake Horsepower Calculator.