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Horsepower Calculator | Compute Horsepower From Torque and RPM

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Estimate horsepower from torque and RPM, or from quarter-mile trap speed and vehicle weight, with the formulas shown. Compare cars, plan modifications and understand the power-to-weight ratio.

Last updated: June 2026 · Free · No sign-up required

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Results

Enter values above and click Calculate to see your result instantly.

Quick reference

Horsepower from torque at RPM:

Torque (lb-ft)3000 rpm5000 rpm
200114 hp190 hp
300171 hp286 hp
400228 hp381 hp

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Interpretation guide

Horsepower facts:

ConceptDetail
1 hp550 ft-lb/s or ~746 watts
HP = TQ at 5252 rpmPower and torque curves cross there
Crank vs wheel HPDrivetrain loses ~10–20%
Trap-speed estimateFrom weight and 1/4-mile speed

lightbulb Worked example — 300 lb-ft at 4,000 RPM

A dyno sheet shows an engine making 300 lb-ft of torque at 4,000 RPM. Horsepower = torque × RPM ÷ 5,252 = 300 × 4,000 ÷ 5,252.

Result: 228.5 hp (≈ 170 kW).

What this means: That is crank horsepower on an engine dyno; expect roughly 15% less at the wheels through a typical drivetrain — about 194 whp. The same 300 lb-ft at 6,000 RPM would make 343 hp, which is why high-revving engines produce big power from modest torque.

Formula & methodology

Formula: HP = Torque(lb-ft) x RPM / 5252; trap estimate: HP = weight x (mph / 234)^3

How horsepower is derived

Two routes, depending on your data. From dyno figures: HP = torque (lb-ft) × RPM ÷ 5,252 — the constant that converts rotational work to horsepower (the torque and power curves cross at 5,252 RPM). From drag-strip data: HP = weight (lb) × (trap speed in mph ÷ 234)³, an empirical estimate.

  • Results also show kilowatts (hp × 0.7457).
  • Wheel horsepower runs roughly 10–15% below crank figures after drivetrain loss.

Use the dyno route when you have torque figures — it is exact physics. The trap-speed route is an estimate for when you only have quarter-mile data.

Authoritative source: timeanddate.com

Frequently asked questions

How do I calculate horsepower from torque?
Enter the required values into the input fields and press the calculate button. The tool applies the formula HP = Torque(lb-ft) x RPM / 5252; trap estimate: HP = weight x (mph / 234)^3 and returns the result with a short explanation of each step, so you can check the working yourself.
Why do horsepower and torque cross at 5252 rpm?
The Horsepower Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Enter torque in foot-pounds and engine RPM, and this horsepower calculator estimates mechanical horsepower using the standard torque formula, then converts the result to kilowatts and watts. It explains the difference between mechanical, metric, and There is no limit on usage, and it works on any device.
What's the difference between crank and wheel horsepower?
Crank (brake) horsepower is the engine's output measured at the flywheel before drivetrain losses; wheel horsepower is what actually reaches the tires through the transmission, driveshaft, and axles. Typical drivetrain losses are 10–15% for rear-wheel drive and 15–20% for front- or all-wheel drive. Dyno numbers are usually wheel horsepower, while manufacturers quote crank figures.
How is horsepower estimated from a quarter mile?
Empirical formulas relate trap speed and vehicle weight to horsepower, such as HP = weight × (trap speed ÷ 234)³, since a faster trap speed at the same weight requires proportionally more power. These estimates are accurate to roughly ±5% for conventional cars. Enter your quarter-mile trap speed and weight and the calculator applies the formula.
How many watts is one horsepower?
One mechanical horsepower equals exactly 745.7 watts (0.7457 kW), by definition. One metric horsepower (PS) equals 735.5 watts — slightly less. In electrical contexts, 1 hp is commonly approximated as 746 watts for sizing motors. The calculator converts between horsepower units and kilowatts so specs from different countries compare cleanly.
Why does the calculator ask for RPM and not just torque?
Because horsepower is torque applied over time — the same 300 lb-ft makes 114 hp at 2,000 RPM but 343 hp at 6,000 RPM. Without RPM, torque alone cannot tell you power. That is also why diesels (big torque, low RPM) and sport bikes (small torque, high RPM) can post similar horsepower.
Why are there two different horsepower formulas?
They answer different questions. Torque × RPM ÷ 5,252 computes power from measured engine output (dyno data). Weight × (trap speed ÷ 234)³ estimates it backwards from quarter-mile performance when you don't have dyno numbers. Use the dyno route when you have torque figures — it is exact, not empirical.
Is my data sent anywhere when I calculate?
No — the calculation runs on the page itself, so your numbers never leave your device.
How precise is the result?
The torque formula is exact physics: 300 lb-ft at 4,000 RPM is exactly 228.5 hp. The trap-speed estimate is empirical and typically lands within ±10%. Real-world crank-vs-wheel differences (drivetrain loss of ~10–15%) matter more than arithmetic precision.

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