Horsepower, Torque, and RPM Calculator
Pick what you want to calculate, enter the other two values, and click Calculate.
Formula used: HP = (Torque × RPM) ÷ 5252
What this hp and torque calculator does
This calculator helps you quickly solve the classic engine equation linking horsepower, torque, and RPM. It is useful for car enthusiasts, motorcycle tuners, dyno readers, and students learning powertrain basics. If you know any two values, you can calculate the third instantly.
Horsepower vs. torque: what is the difference?
Torque is rotational force
Torque tells you how strongly the crankshaft is being twisted. In the imperial system, torque is usually measured in pound-feet (lb-ft). More torque generally means stronger pull, especially at lower RPM.
Horsepower is the rate of doing work
Horsepower combines force and speed. You can think of it as how quickly torque is being applied over time. That is why RPM matters: an engine can make similar torque at two different speeds, but the faster speed produces more horsepower.
The core formula
In imperial units, the relationship is:
- HP = (Torque × RPM) / 5252
- Torque = (HP × 5252) / RPM
- RPM = (HP × 5252) / Torque
The number 5252 comes from unit conversion constants in the horsepower definition. On a dyno chart using horsepower and lb-ft, the HP and torque lines always cross at 5252 RPM.
How to use this calculator correctly
- Select what you want to calculate: HP, torque, or RPM.
- Enter the other two values with positive numbers.
- Click Calculate to see your answer.
- Use Reset to clear all fields and start over.
Example calculations
Example 1: Find horsepower
If torque is 400 lb-ft at 5,000 RPM:
HP = (400 × 5000) / 5252 = 380.81 HP
Example 2: Find torque
If horsepower is 300 HP at 4,500 RPM:
Torque = (300 × 5252) / 4500 = 350.13 lb-ft
Example 3: Find RPM
If horsepower is 450 HP and torque is 420 lb-ft:
RPM = (450 × 5252) / 420 = 5,627.14 RPM
Common mistakes to avoid
- Mixing wheel horsepower and crank horsepower in the same comparison.
- Using Newton-meters (N·m) without converting when the formula expects lb-ft.
- Forgetting that horsepower depends heavily on RPM.
- Entering zero or negative values, which are not valid for this simple calculator.
Quick FAQ
Why do HP and torque cross at 5252 RPM?
Because of how horsepower is defined in imperial units. The constant 5252 causes the values to be equal at exactly 5252 RPM when torque is in lb-ft.
Can I use this for motorcycles and small engines?
Yes. The same relationship works for any rotating engine as long as your units are consistent.
What if my torque is in N·m?
Convert first: 1 lb-ft = 1.35582 N·m. After converting to lb-ft, use the calculator normally.
Final thoughts
A good hp and torque calculator makes tuning conversations clearer and helps you read dyno charts with confidence. Whether you are comparing builds, selecting gearing, or just learning engine math, this tool gives you quick and accurate power relationships in seconds.