HP to in-lb/sec Calculator
Convert horsepower to inch-pounds per second instantly.
This converter expresses horsepower in inch-pounds per second — a convenient unit for small motors, actuators, and precision mechanisms where inch-pounds are the natural torque unit.
HP to in-lb/sec Formula
How to Use This Calculator
- Enter horsepower.
- Read inch-pounds per second.
Worked Example
How This Unit Relates to Horsepower's Definition
Horsepower was defined as 550 foot-pounds of work per second (or 33,000 per minute). Multiply 550 by the 12 inches in a foot and you get 6,600 inch-pounds per second — the same power expressed in a finer unit. It's a work-rate unit, distinct from torque in inch-pounds: this describes energy delivered over time, not a static twisting force.
Practical Uses
Inch-pound-per-second figures appear in small-scale mechanical engineering, actuator and servo specifications, and physics work where inches are the working length unit. It lets you keep an entire calculation in inch-pound units rather than switching to feet or watts midway.
HP to in-lb/sec
| Horsepower | in-lb/sec | ft-lb/sec |
|---|---|---|
| 0.5 | 3,300 | 275 |
| 1 | 6,600 | 550 |
| 2 | 13,200 | 1,100 |
| 5 | 33,000 | 2,750 |
Inch-Pounds Per Second Is Not Inch-Pounds
This is the single most common error with these units, and it produces answers that are wrong by whatever the RPM happens to be. Inch-pounds measure torque — a twisting effort that exists whether or not anything moves. Inch-pounds per second measure power — a rate of doing work, which requires motion by definition.
| Inch-pounds (in-lb) | Inch-pounds per second (in-lb/sec) | |
|---|---|---|
| What it measures | Torque, or twisting effort | Power, or the rate of doing work |
| Needs motion? | No — a tightened bolt holds torque at rest | Yes — nothing moving means zero power |
| Depends on RPM? | No, it is a standalone value | Yes, it already contains the speed |
| Converts to horsepower | Only with an RPM figure | Directly: divide by 6,600 |
| Typical use | Fastener specifications, motor output torque | Work-rate ratings on small drives and actuators |
The practical test is simple: if a figure changes when the shaft speeds up, it is power. If it doesn't, it is torque. A bolt torqued to 90 in-lb stays at 90 in-lb whether the engine is running or parked. If you've a torque figure and need horsepower from it, the HP to inch-pounds torque calculator is the tool you want, because it asks for the RPM this one doesn't need.
The Full Work-Rate Unit Ladder
One horsepower can be written several ways depending on which length and time units the specification uses. They're all the same quantity:
| Unit | Value for 1 HP | Relationship |
|---|---|---|
| Foot-pounds per minute | 33,000 | The original definition |
| Foot-pounds per second | 550 | 33,000 ÷ 60 |
| Inch-pounds per second | 6,600 | 550 × 12 |
| Inch-pounds per minute | 396,000 | 33,000 × 12 |
| Watts | 745.7 | The SI equivalent |
| Kilowatts | 0.7457 | 745.7 ÷ 1,000 |
Converting between any two is a matter of multiplying or dividing by 12 for the length unit and 60 for the time unit. The most frequent slip is dropping the factor of 60 between per-second and per-minute figures, which puts the answer out by a factor of sixty rather than a plausible-looking margin — usually obvious enough to catch. The factor of 12 error is more dangerous, because a result twelve times too large can still look believable on a small motor. For the metric route, use the watts to HP calculator.
Where You Actually Meet This Unit
Inch-pounds per second appears where the equipment is small enough that feet are an awkward unit but the specification still needs to express a rate of work. In practice that means a handful of specific places:
| Application | Typical range | Why this unit |
|---|---|---|
| Small gearmotors and actuators | 100–3,000 in-lb/sec | Output measured in inches keeps the numbers manageable |
| Linear actuators and screw jacks | 200–6,000 in-lb/sec | Travel is specified in inches per second already |
| Instrument and servo drives | 10–500 in-lb/sec | Fractional horsepower figures would be unwieldy |
| Engineering coursework | Any | Tests whether the student can track units correctly |
In each case the choice is about keeping the numbers readable. A servo drive rated at 0.015 horsepower is hard to compare against anything; the same drive at 99 in-lb/sec sits in a range the reader can hold in their head. That's the entire reason the unit persists.
Working Through a Full Conversion
Suppose a gearmotor datasheet gives 2,400 in-lb/sec and you need to compare it against a motor quoted in watts. The chain runs in two steps, and doing it explicitly makes any error obvious:
0.364 × 745.7 = 271 W
A useful cross-check: 2,400 in-lb/sec divided by 12 gives 200 ft-lb/sec, and 200 divided by 550 gives the same 0.364 HP. Two independent routes to the same number is the fastest way to confirm you haven't misplaced a factor of twelve.
Frequently Asked Questions
One horsepower equals 6,600 inch-pounds per second, which is 550 foot-pounds per second multiplied by 12 inches per foot.
Multiply horsepower by 6,600.
It's useful for small motors, servos, and actuators where torque is naturally measured in inch-pounds rather than foot-pounds.
One foot-pound equals 12 inch-pounds, so 550 ft-lb/sec (1 HP) equals 6,600 in-lb/sec.
Divide inch-pounds per second by 6,600.
No, and confusing them is the most common error with these units. Inch-pounds measure torque, a twisting effort that exists even at rest. Inch-pounds per second measure power, a rate of doing work that requires motion. The practical test is whether the figure changes when the shaft speeds up: if it does, it is power.
396,000 in-lb/min, which is 33,000 foot-pounds per minute multiplied by 12. The per-second figure is 6,600. Dropping the factor of 60 between them is a frequent slip, though it puts the answer out by enough to be obvious.
Readability on small equipment. A servo drive rated at 0.015 horsepower is hard to compare against anything, while the same drive at 99 in-lb/sec sits in a range you can hold in your head. Small gearmotors, linear actuators and instrument drives all use it for that reason.