200 lb-ft at 4500 RPM — Horsepower
Use the calculator below to try other torque and RPM combinations, or switch to a quarter-mile-based estimate.
Horsepower
171.4 hp
Example
200 lb-ft of torque at 4,500 RPM produces 171.4 horsepower.
Metric hp (PS)
173.7
Kilowatts
127.8
Boiler hp
13.03
Power in different units
What is a Horsepower Calculator?
Horsepower measures the rate at which an engine does work — how quickly it can convert fuel into motion, not just how much force it produces. This calculator supports the direct dynamometer-style method (from torque and RPM) as well as two estimation methods based on quarter-mile drag racing results, which are commonly used when a dyno isn't available.
Horsepower Across the RPM Range
Holding torque constant at 200 lb-ft, this shows how horsepower rises with RPM — real engines don't hold torque perfectly flat across the rev range, but this illustrates why horsepower and RPM are directly linked in the formula.
How Is Horsepower Calculated?
The torque/RPM method is the direct, dynamometer-accurate formula. The two quarter-mile methods are statistical approximations derived from analyzing large numbers of real drag strip runs — useful estimates, but not as precise as an actual dyno measurement.
HP ≈ Weight ÷ (ET ÷ 5.825)³ | HP ≈ Weight × (Trap Speed ÷ 234)³
Why 5252 Specifically
5252 comes from converting the physics definition of power (force × angular velocity) into the units mechanics actually use — pound-feet of torque and revolutions per minute. It's also why torque and horsepower curves always cross at exactly 5252 RPM on a dyno chart: below that RPM, torque numerically exceeds horsepower, and above it, horsepower exceeds torque.
Why Two Different Quarter-Mile Formulas Exist
The elapsed-time (ET) method and trap-speed method are independent statistical fits, so they won't always agree exactly for a real vehicle — differences in gearing, tire traction, and driver skill affect ET more than trap speed, since trap speed is measured at a single instant (the finish line) while ET accumulates every inefficiency across the whole run. Trap speed is generally considered the more reliable of the two for horsepower estimation.
Mechanical vs. Metric Horsepower
"Horsepower" in the US typically means mechanical (imperial) horsepower. Many countries instead rate engines in metric horsepower (PS, from the German "Pferdestärke"), which is about 1.4% smaller than mechanical horsepower — a car rated "300 PS" is very close to, but not exactly, 300 mechanical hp. Kilowatts are the SI-standard unit and are increasingly used in official spec sheets worldwide.
Example — Your Current Inputs
200 lb-ft of torque at 4,500 RPM produces 171.4 horsepower.
Additional Example — A Stock V8 Sedan
A typical stock V8 sedan producing 350 lb-ft of torque at 4,500 RPM makes about 300 horsepower at that engine speed. The same engine's peak horsepower usually occurs at a higher RPM than peak torque, since horsepower keeps climbing as RPM rises even after torque itself starts to taper off — right up until RPM gains stop outpacing the torque drop-off.
About These Parameters
- Torque & RPM
- Torque is the twisting force an engine produces; RPM is the engine speed at which that specific torque figure was measured. Horsepower always depends on both — the same torque figure produces different horsepower at different RPMs.
- Vehicle Weight & Quarter-Mile Result
- Both quarter-mile methods need the vehicle's actual raced weight (including driver) since a heavier vehicle needs more power to produce the same elapsed time or trap speed as a lighter one.
Frequently Asked Questions
Which quarter-mile method is more accurate?
Trap speed is generally considered more reliable, since it's a single instantaneous measurement less affected by launch technique, gearing, and traction than elapsed time, which accumulates every inefficiency across the entire run.
Why do horsepower and torque curves always cross at 5252 RPM?
It's a direct consequence of the formula's constant: whenever RPM equals 5252, HP = Torque × 5252 ÷ 5252 = Torque, so the two numbers are mathematically forced to be equal at that exact engine speed, regardless of the engine.
Do quarter-mile estimates account for aerodynamic drag or tire size?
No — these are simplified statistical formulas based on weight alone. Real-world factors like aerodynamics, tire compound, altitude, and drivetrain losses all shift the actual relationship, which is why these methods are treated as estimates rather than precise measurements.