HP to in-lbs Torque Calculator
Convert horsepower and RPM into torque in inch-pounds.
This calculator finds torque in inch-pounds from horsepower and RPM — useful for small motors and gearmotors where torque is rated in inch-pounds rather than foot-pounds.
HP to in-lbs Torque Formula
How to Use This Calculator
- Enter horsepower.
- Enter RPM.
- Read torque in inch-pounds (and lb-ft).
Worked Example
When Inch-Pounds Are Used
Inch-pounds are the natural torque unit for small motors, gearmotors, servos, and precision mechanisms where foot-pounds would be awkwardly small fractions. Power-tool makers, fractional-horsepower motor manufacturers, and fastener specs for delicate assemblies all quote torque in in-lb. Since there are 12 inches in a foot, in-lb is simply lb-ft × 12.
HP to Inch-Pounds at 1,750 RPM
| Horsepower | Torque (lb-ft) | Torque (in-lb) |
|---|---|---|
| 0.5 | 1.5 | 18 |
| 1 | 3.0 | 36 |
| 5 | 15.0 | 180 |
| 10 | 30.0 | 360 |
Torque depends on RPM, so the same horsepower yields more torque at lower speeds — a key reason gear reduction is used to boost torque in compact drives.
How Much RPM Changes the Answer
Because torque is inversely proportional to speed, the RPM figure matters more than the horsepower figure for most practical questions. Here's a single 2 HP motor rated at different speeds, which is exactly the choice you face when specifying a gearmotor:
| Speed | Torque (in-lb) | Torque (lb-ft) | Torque (Nm) |
|---|---|---|---|
| 100 RPM | 1,260 | 105.0 | 142.4 |
| 250 RPM | 504 | 42.0 | 57.0 |
| 500 RPM | 252 | 21.0 | 28.5 |
| 1,150 RPM | 110 | 9.1 | 12.4 |
| 1,750 RPM | 72 | 6.0 | 8.1 |
| 3,450 RPM | 37 | 3.0 | 4.1 |
The span is nearly thirty-five to one across ordinary motor speeds, from the same two horsepower. That's why a horsepower rating without a speed tells you almost nothing about whether a motor will turn your load. It's also why gearboxes exist. Cut output speed by a factor of ten and available torque multiplies by roughly the same factor, minus gear losses. Work the reduction out with the output torque calculator.
Inch-Pounds, Foot-Pounds, Inch-Ounces and Newton-Meters
Small-equipment specifications rotate between four torque units, and mixing them up is easy because the numbers are all in similar ranges. These are the conversions worth memorising:
| From | To | Multiply by | Where each is used |
|---|---|---|---|
| Foot-pounds | Inch-pounds | 12 | Automotive to small-motor specifications |
| Inch-pounds | Inch-ounces | 16 | Stepper motors and instrument drives |
| Inch-pounds | Newton-meters | 0.11298 | Imperial to metric datasheets |
| Newton-meters | Inch-pounds | 8.8507 | Metric to imperial datasheets |
| Foot-pounds | Newton-meters | 1.35582 | Engine and fastener specifications |
Inch-ounces catch people out most often. A stepper motor rated at 200 oz-in is only 12.5 in-lb, so treating the two as equivalent overstates the motor by a factor of sixteen. Where a figure looks implausibly large for the physical size of the device, an ounce-inch rating read as inch-pounds is usually the explanation. The Nm to lb-ft converter handles the metric side directly.
Why Fastener Specifications Use Inch-Pounds
Torque wrench specifications for small fasteners are almost always given in inch-pounds rather than foot-pounds, and the reason is resolution rather than tradition. A bolt specified at 7.5 lb-ft becomes 90 in-lb, and a whole number is far easier to set accurately on a click-type wrench than a decimal.
This is also why inch-pound torque wrenches exist as a separate tool class. A wrench with a range of 40 to 200 in-lb covers small fasteners with far better accuracy than a foot-pound wrench operating at the very bottom of its scale, where click-type mechanisms are least reliable.
Inch-Pounds Versus Inch-Pounds Per Second
These two look almost identical in a specification and mean completely different things. Inch-pounds are torque: a twisting effort that exists whether or not anything is turning. Inch-pounds per second are power: a rate of doing work, which requires motion.
The distinction has a practical consequence for this calculator. Torque conversion needs an RPM figure because horsepower already contains speed and you've to divide it back out. A work-rate figure in inch-pounds per second already has the speed baked in, so it converts to horsepower by simple division with no RPM required — one horsepower is exactly 6,600 in-lb/sec. If that's the figure on your datasheet, use the HP to in-lb/sec calculator instead of this one.
Frequently Asked Questions
First find torque in lb-ft using (HP × 5252 ÷ RPM), then multiply by 12 to get inch-pounds. You need the RPM.
Torque depends on the speed at which power is delivered. The same horsepower produces different torque at different RPM.
Twelve. One foot-pound of torque equals 12 inch-pounds.
For small motors, gearmotors, and fasteners where foot-pounds would be awkwardly small numbers.
Convert in-lb to lb-ft (divide by 12), then use HP = (lb-ft × RPM) ÷ 5252.
Sixteen. A stepper motor rated at 200 oz-in is only 12.5 in-lb, so reading ounce-inches as inch-pounds overstates the motor by a factor of sixteen. Where a torque figure looks implausibly large for the physical size of the device, that mix-up is usually the cause.
Resolution. A bolt specified at 7.5 lb-ft becomes a clean 90 in-lb, and whole numbers are far easier to set accurately on a click-type wrench. It also matters for safety: reading 90 in-lb as 90 lb-ft applies twelve times the intended load and will strip threads or snap the bolt.
Enormously, because torque is inversely proportional to speed. A single 2 HP motor gives 1,260 in-lb at 100 RPM but only 37 in-lb at 3,450 RPM — a span of nearly thirty-five to one. This is why a horsepower rating without a speed tells you almost nothing about whether a motor will turn your load.
Inch-pounds are torque and inch-pounds per second are power. Torque conversion needs an RPM figure because horsepower already contains speed and you've to divide it back out. A work-rate figure already includes the speed, so it converts directly: one horsepower is exactly 6,600 in-lb/sec.