Calculate HP from torque and RPM, convert between HP, kW, and PS (metric horsepower), estimate wheel horsepower from crank HP, predict 0-60 mph times, and calculate power-to-weight ratio. Five precision modes covering every horsepower calculation.
✓Verified: SAE J1349 Engine Power Standards & NIST Conversion Factors
📋 Enter Any Two Values to Solve for the Third
ft‑lb
Peak torque value
Enter torque value.
RPM
RPM where torque occurs
Enter RPM value.
HP
Leave blank to calculate HP
ℹ️ Enter any two values — the third will be calculated. Torque & RPM → HP. HP & RPM → Torque. HP & Torque → RPM.
⚠️ Disclaimer: All calculations use standard SAE formulas and published conversion factors. Quarter-mile and 0-60 estimations are approximations — actual performance varies significantly with traction, altitude, temperature, fuel, and driver skill. Use for educational and comparative purposes.
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Sources & Methodology
✓All formulas verified against SAE International standards. Conversion factors from NIST. Quarter-mile and ET formulas from published drag racing literature.
SAE J1349 is the industry standard for engine power measurement in North America, defining the HP = (Torque x RPM) / 5,252 formula, the 5,252 constant derivation, test conditions, and correction factors used by all US manufacturers for power ratings.
National Institute of Standards and Technology official conversion factors: 1 HP = 0.74569987 kW (exact mechanical horsepower). 1 PS = 0.7354988 kW. All unit conversions use NIST-published exact values.
National Hot Rod Association published ET and trap speed horsepower estimation formulas (ET method: HP = Weight / (ET/5.825)^3 and Hale trap speed method: HP = Weight x (Trap/234)^3) referenced for the quarter-mile calculation modes.
Methodology:HP = (Torque ft-lb × RPM) / 5,252 | Torque = (HP × 5,252) / RPM | RPM = (HP × 5,252) / TorqueHP ↔ kW: ×0.7457 (HP to kW) | HP ↔ PS: ×1.0139 (HP to PS) | 1 HP = 550 ft-lb/secWHP = BHP × (1 − drivetrain loss%) | ET method: HP = Weight / (ET/5.825)^3Trap Speed (Hale): HP = Weight × (Trap mph / 234)^3Power-to-Weight = HP / Weight(lbs) | lb/HP = Weight / HP
0-60 estimate: time = 3.0 + (lb/HP - 7) × 0.18 × drivetrain/transmission factors. AWD ×0.90, manual ×0.95, EV ×0.80 applied to base estimate.
How to Calculate Engine Horsepower — The Complete Formula Guide
Horsepower is the most universally recognized indicator of engine performance, yet most people never calculate it themselves. Understanding the formulas behind the number demystifies dyno sheets, spec sheets, and performance claims — and lets you work out power relationships between torque, RPM, drivetrain losses, and actual vehicle performance.
HP = (Torque in ft-lb × RPM) / 5,252
Where does 5,252 come from?
James Watt defined 1 horsepower = 33,000 ft-lb per minute. One rotation = 2π radians.
Torque × angular velocity = Power: HP = (T × RPM × 2π) / 33,000
Simplify: 33,000 / (2π) = 5,252.11 — the constant is mathematically exact from Watt's definition.
At exactly 5,252 RPM: HP and torque (ft-lb) are always numerically equal.
HP, BHP, WHP — Understanding the Three Horsepower Measurements
When an automaker claims "400 horsepower," they mean brake horsepower (BHP) — measured at the engine crankshaft on a dynamometer under SAE J1349 standardized conditions. This is the raw engine output before any power is consumed by the transmission, driveshaft, and differential. Wheel horsepower (WHP) — measured at the drive wheels — is what actually propels the vehicle, and it is always less than BHP due to drivetrain losses.
Drivetrain
Typical Loss
400 BHP = WHP
Example Vehicles
Rear-wheel drive (RWD)
12–15%
340–352 WHP
Mustang GT, Corvette, BMW M3
Front-wheel drive (FWD)
13–16%
336–348 WHP
Civic Type R, VW Golf R (FWD mode)
All-wheel drive (AWD)
17–22%
312–332 WHP
Audi RS models, Subaru WRX
Four-wheel drive (4WD)
18–23%
308–328 WHP
Raptor, Ram TRX, Ram Power Wagon
HP vs kW vs PS — International Power Unit Comparison
Three different power units appear in automotive specs depending on the market. SAE HP (used in the US) differs slightly from PS (used in Germany, France, Italy) and both differ from kW (the SI unit used globally in engineering). The differences are small but meaningful when comparing specs across markets.
Unit
Definition
1 HP equals
300 HP equals
Used In
HP (SAE)
550 ft-lb/second
1.000 HP
300 HP
USA, Canada
kW
1,000 joules/second
0.7457 kW
223.7 kW
Global (SI unit)
PS / CV
75 kg·m/second
1.0139 PS
304.2 PS
Europe, Japan (bhp)
Quarter-Mile HP Estimation — ET Method and Trap Speed Method
When a dyno is not available, two field-proven formulas estimate wheel horsepower from quarter-mile data. The ET method uses elapsed time; the Hale formula uses trap speed at the end of the quarter mile. Both estimate wheel HP — multiply by approximately 1.15 (RWD) to estimate crank HP.
Method
Formula
Best For
Accuracy
ET Method
HP = Weight / (ET / 5.825)^3
Naturally aspirated, street cars
±5–10%
Hale Trap Speed
HP = Weight × (Trap mph / 234)^3
Any powertrain type
±5–8%
Power-to-Weight Ratio — The Real Performance Number
Raw horsepower without context is misleading. A 400 HP truck and a 400 HP sports car feel completely different because their power-to-weight ratios are different. The lb/HP metric (lighter = better) is the true performance benchmark used by engineers, racers, and car reviewers to compare vehicles across size classes.
Performance Class
lb/HP Ratio
0-60 Estimate
Examples
Economy
>20 lb/HP
9–14 sec
Toyota Corolla, Honda Fit, Civic base
Average performance
14–20 lb/HP
6.5–9 sec
V6 Accord, Camry XSE, Explorer ST
Quick
10–14 lb/HP
4.5–6.5 sec
Mustang GT, BMW M340i, Charger R/T
Sports / muscle
7–10 lb/HP
3.5–4.5 sec
Corvette C8, GT500, BMW M3
Supercar
4–7 lb/HP
2.5–3.5 sec
Ferrari 488, Lamborghini Huracan
Hypercar
<4 lb/HP
<2.5 sec
Bugatti Chiron, Rimac Nevera, Koenigsegg
Horsepower and Torque: Which Wins Races, Which Wins Drag Strips?
The horsepower vs torque debate is one of the most persistent in automotive culture — and the answer depends entirely on what you are measuring. Torque is what accelerates you from a stop and at low RPM. Horsepower determines your top speed and sustained acceleration at high RPM. In drag racing: torque wins the launch, horsepower wins the top half of the quarter mile. In road racing: horsepower sustained through a broad RPM band dominates because corner exit speed and high-RPM pull matter most. Electric vehicles demonstrate this clearly — they have enormous instantaneous torque (which is why they win launches against much more powerful ICE cars) but their HP figure governs sustained high-speed performance.
💡 The 5,252 RPM fact: On any power curve graph, the HP line and torque line will always cross at exactly 5,252 RPM — regardless of the engine's displacement, tune, or character. This is a mathematical constant of the relationship between horsepower and torque, not a coincidence. High-revving sports car engines produce their peak HP well above 5,252 RPM; diesel engines produce theirs well below it.
Frequently Asked Questions
HP = (Torque in ft-lb x RPM) / 5,252. The constant 5,252 comes from James Watt's definition (1 HP = 33,000 ft-lb/min) combined with rotational mechanics (2π radians per revolution). At exactly 5,252 RPM, HP and ft-lb torque numbers are always numerically equal. Enter torque and RPM into Mode 1 above — it also solves for torque if you know HP and RPM, or finds RPM if you know HP and torque.
Multiply HP by 0.7457 to get kW. Multiply kW by 1.3410 to get HP. Example: 350 HP = 350 x 0.7457 = 261.0 kW. The conversion factor 0.7457 is the NIST-published exact mechanical horsepower value. Use Mode 2 above to convert instantly between HP, kW, PS (metric horsepower), and ft-lb/second simultaneously.
HP is the general term. BHP (brake horsepower) = measured at the crankshaft with a brake dynamometer — the advertised power rating. WHP (wheel horsepower) = measured at the driven wheels on a chassis dyno, after drivetrain losses. WHP is typically 12 to 22% lower than BHP. A car rated at 400 BHP produces approximately 340-352 WHP (RWD) at the contact patch. Use Mode 3 to convert BHP to WHP for your drivetrain type.
PS (Pferdestärke) is the European metric horsepower used by most European manufacturers. 1 HP = 1.0139 PS. They are very close but not identical: 300 HP = 304.2 PS. This means a European car rated at 300 PS actually produces 295.9 HP by SAE measurement. When comparing specs across markets, be aware of the unit — PS is common in German, French, and Italian car specs. CV (cheval-vapeur) in French and Italian specs is identical to PS.
Power-to-weight ratio = HP / vehicle weight. Express as HP/lb (higher = better) or lb/HP (lower = better). Example: 400 HP in a 3,200 lb car = 0.125 HP/lb or 8.0 lb/HP. Performance benchmarks: under 10 lb/HP = sports/muscle car territory. 10-14 lb/HP = quick everyday car. 15-20 lb/HP = average family car. Over 20 lb/HP = economy car or heavy vehicle. Use Mode 5 (Power-to-Weight) to calculate your ratio and get a 0-60 estimate.
ET method: HP = Weight / (ET / 5.825)^3. Example: 3,400 lb car, 13.5 sec ET: HP = 3,400 / (13.5/5.825)^3 = 3,400 / 12.44 = 273 WHP. This estimates wheel HP — multiply by 1.15 for RWD crank HP estimate. Accuracy: ±5-10% for naturally aspirated street cars. Less accurate for turbocharged or AWD vehicles. Use Mode 4 (ET / Trap Speed) above.
Hale formula: HP = Weight x (Trap mph / 234)^3. Example: 3,400 lb car, 100 mph trap: HP = 3,400 x (100/234)^3 = 3,400 x 0.0781 = 265 WHP. The Hale formula is generally considered slightly more accurate than the ET method for stock vehicles because trap speed is less affected by launch technique. Enter your data into Mode 4 and select "Trap Speed Method."
The 5,252 crossover is a mathematical constant. HP = Torque x RPM / 5,252. When HP equals Torque (numerically), the equation becomes 1 = RPM / 5,252, therefore RPM = 5,252. This is true for ANY engine — regardless of displacement, tune, or character. The crossover has nothing to do with the engine's performance characteristics; it is pure math from Watt's original horsepower definition.
Electric motors have very low drivetrain losses because they are integrated directly with the drive unit — typically 5 to 10% loss versus 12 to 22% for ICE vehicles. A Tesla Model S Plaid rated at 1,020 HP produces approximately 900 to 970 WHP. More importantly, EVs deliver peak torque instantaneously from 0 RPM — this is why a 450 HP EV can outrun a 600 HP ICE car from a stop: the torque delivery advantage at launch RPM is enormous.
HP = Torque x RPM / 5,252 is mathematically exact — the same formula used on every dyno sheet. If you have accurate torque and RPM data, the result is precise. The approximation comes from using peak values from spec sheets: manufacturers typically quote peak torque at one RPM and peak HP at a different RPM. These peaks don't occur simultaneously. For accurate BHP, use a chassis dyno. This calculator's Torque/RPM mode is exact for the values entered.