Convert Horsepower to Milliwatts
1 horsepower is 745,699.87 mW. One horsepower is exactly 745699.871582 milliwatts.
One horsepower is 745699.87 milliwatts. To convert horsepower to milliwatts, multiply by 745699.87; to go the other way, divide by 745699.87 or multiply by 1.3410 × 10^-6. The relation is exact but the figure is not: it is a rounding of a number that does not terminate, and it follows from NIST Special Publication 811. Mechanical horsepower: exactly 550 foot-pounds of work every second, the figure James Watt settled on to sell engines against pit ponies.
Factor checked against the defining standard · How we check
- Horsepower × 745699.87
1 * 745699.87745,699.872 mW
1 horsepower in every power unit
| Unit | Value | Exact factor |
|---|---|---|
| horsepower (as entered) | 1 hp | — |
| metric horsepower | 1.013869665 PS | × 1.01386966542 |
| watts | 745.6998716 W | × 745.699871582 |
| kilowatts | 0.7456998716 kW | × 0.745699871582 |
| milliwatts | 745,699.8716 mW | × 745,699.871582 |
| megawatts | 0.0007456998716 MW | × 0.000745699871582 |
| tons of refrigeration | 0.2120361315 TR | × 0.21203613147 |
| BTU per hour | 2,544.433578 BTU/h | × 2,544.43357764 |
Factors are entered by hand from NIST Special Publication 811 rather than derived from a units library, so the ones that terminate are exact rather than rounded.
How do you convert horsepower to milliwatts? The converter and the working
- 1.Take the measurement in horsepower.
- 2.Multiply by 745699.87 — that is how many milliwatts fit in one horsepower.
- 3.To go back the other way, divide by 745699.87, or multiply by 1.3410 × 10^-6.
Worked example: 25 horsepower to milliwatts
- Formula
- hp × 745699.87 = mW
- Arithmetic
- 25 × 745699.87 = 18,642,496.79 mW
- Answer
- 25 hp = 18,642,496.79 mW
The factor is rounded for display; the figure above is computed from the full value.
Horsepower to milliwatts conversion table
| Horsepower | Milliwatts |
|---|---|
| 1 hp | 745,699.87 mW |
| 2 hp | 1,491,399.74 mW |
| 3 hp | 2,237,099.61 mW |
| 4 hp | 2,982,799.49 mW |
| 5 hp | 3,728,499.36 mW |
| 6 hp | 4,474,199.23 mW |
| 7 hp | 5,219,899.1 mW |
| 8 hp | 5,965,598.97 mW |
| 9 hp | 6,711,298.84 mW |
| 10 hp | 7,456,998.72 mW |
| 12 hp | 8,948,398.46 mW |
| 15 hp | 11,185,498.07 mW |
| 20 hp | 14,913,997.43 mW |
| 25 hp | 18,642,496.79 mW |
| 50 hp | 37,284,993.58 mW |
| 100 hp | 74,569,987.16 mW |
| 200 hp | 149,139,974.32 mW |
| 300 hp | 223,709,961.47 mW |
| 500 hp | 372,849,935.79 mW |
| 1000 hp | 745,699,871.58 mW |
| 2000 hp | 1,491,399,743.16 mW |
| 5000 hp | 3,728,499,357.91 mW |
| 10000 hp | 7,456,998,715.82 mW |
What is a horsepower?
Mechanical horsepower: exactly 550 foot-pounds of work every second, the figure James Watt settled on to sell engines against pit ponies. US vehicle and motor ratings use it.
What is a milliwatt?
A thousandth of a watt. Radio transmit power, laser output and audio signal levels are all quoted in it, and dBm is referenced to exactly one.
How many milliwatts are in a horsepower?
One horsepower is 745699.87 milliwatts. Going the other way, one milliwatt is 1.3410 × 10^-6 horsepower. Both figures come from the same defined relation rather than from a measurement, which is why they are the same today as they were in 1959.
Every power unit here
The whole group — 8 units with their symbols and the size of each one in watts — is on the conversion index, along with every pair it makes. The table above already gives each of them relative to a horsepower.
Source: NIST Special Publication 811 — mechanical horsepower is 550 ft·lbf/s exactly
Cite this page
- APA
- Rule Calculator. (2026). Convert Horsepower to milliwatts. Rule Calculator. https://rulecalculators.com/convert/horsepower-to-milliwatt
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- "Convert Horsepower to milliwatts." Rule Calculator, August 16, 2026, https://rulecalculators.com/convert/horsepower-to-milliwatt.
- Chicago
- Rule Calculator. "Convert Horsepower to milliwatts." Rule Calculator. Last reviewed August 16, 2026. https://rulecalculators.com/convert/horsepower-to-milliwatt.
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Questions people actually ask
- How many milliwatts are in a horsepower?
- 745699.87. A thousandth of a watt. Radio transmit power, laser output and audio signal levels are all quoted in it, and dBm is referenced to exactly one.
- How do I convert milliwatts back to horsepower?
- Divide by 745699.87, or multiply by 1.3410 × 10^-6 — they are the same operation.
Other power conversions
Milliwatts to horsepower — the same conversion the other way.