Watt to Horsepower Formula
hp(mech) = W ÷ 745.6998715822702
Conversion factors follow SI relationships published by BIPM and IEC, where those standards apply.
Electrical: hp(E) = W ÷ 746. Metric: hp(M) = W ÷ 735.49875. Reverse mechanical: W = hp × 745.6998715822702.
Watt to Horsepower Converter
Quick Answer
1 W = 0.00134102 hp
Formula: Horsepower = Watt x 0.00134102
Quick values
Sources
- BIPM SI Brochure — Definitions of the pascal, watt, and other SI derived units.
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI), including appendix conversion factors.
- NIST SI units of power — Watt is the SI derived unit of power (J/s). Horsepower is a non-SI unit; cite the convention in use.
Worked examples
- 746 W (1 electrical hp): 746 ÷ 745.6998715822702 = 1.0004 hp(mech)
- 1 500 W shop tool: 1500 ÷ 745.6998715822702 = 2.0115 hp(mech)
- 7 460 W motor: 7460 ÷ 745.6998715822702 = 10.004 hp(mech)
What is watts to horsepower?
The watt is the SI power unit (J/s). Divide watts by 745.69987 for mechanical hp, 746 for electrical hp, or 735.49875 for metric hp (PS).
Formulahp(mech) = W ÷ 745.6998715822702
Key conversions
- 1 000 W = 1.3410 mechanical hp
- 1 electrical hp = 746 W exactly
- 1 metric hp (PS) = 735.49875 W
How many horsepower is 1 000 watts?
One watt is the SI power unit: one joule per second (BIPM). Horsepower is not SI, and three definitions still appear on equipment. This calculator divides watts by mechanical horsepower, 745.6998715822702 W/hp, so 1 000 W = 1.3410 mechanical hp. That is the correct default for engines and most US pump curves.
Two other definitions change the answer. Electrical horsepower is exactly 746 W — NEMA motor nameplates. Metric horsepower (Pferdestärke, cheval-vapeur) is 75 kilogram-force·metres per second = 735.49875 W. A 2 200 W tool is 2.95 mechanical hp, 2.95 electrical hp, or 2.99 metric hp. Pick the convention the datasheet used; do not average them.
Category hub: Power Conversion · Conversion charts · Conversion formulas
Mechanical, electrical, and metric horsepower
Mechanical horsepower is 550 ft·lbf/s. It is what “hp” means on this site unless a unit key says otherwise. Electrical horsepower was standardized at 746 W so that motor current tables stay in round numbers. Metric horsepower (PS) comes from 75 kgf·m/s and is still printed on EU vehicle registration papers. Boiler horsepower (~9 809.5 W) is a steam-generation rate, not shaft power — do not use it here.
Marketing “peak horsepower” on consumer tools is often electrical input watts divided by 746, not measured shaft output. Output hp = (input W × efficiency) ÷ 745.7. A 1 500 W grinder at 70% efficiency is about 1.41 hp at the spindle, not 2.0 hp.
| Definition | Symbol | W per hp | 1 000 W equals |
|---|---|---|---|
| Mechanical | hp | 745.699872 | 1.3410 hp |
| Electrical | hp(E) | 746 | 1.3405 hp(E) |
| Metric (PS / CV) | hp(M) | 735.49875 | 1.3596 hp(M) |
1 000 W expressed in each common horsepower
Watt to Horsepower Conversion Table
Watts to mechanical horsepower (550 ft·lbf/s)
| Watt (W) | Horsepower (hp) |
|---|---|
| 100 W | 0.134102 hp |
| 250 W | 0.335256 hp |
| 500 W | 0.670511 hp |
| 746 W | 1.0004 hp |
| 1000 W | 1.34102 hp |
| 1500 W | 2.01153 hp |
| 2200 W | 2.95025 hp |
| 3730 W | 5.00201 hp |
| 5000 W | 6.70511 hp |
| 7460 W | 10.004 hp |
| 10000 W | 13.4102 hp |
Divide by 746 for electrical hp or 735.49875 for metric hp when the nameplate uses those conventions.
Browse all conversion charts → · Browse conversion formulas →
Practical use cases for Watt to Horsepower
Motor and Drive Selection
Nameplates mix horsepower and kilowatts. Specifying a replacement motor requires converting so the electrical supply and mechanical load match.
Generator and Plant Sizing
Prime-mover ratings may be in horsepower while electrical output is in kW or kVA. Planners convert before comparing mechanical and electrical capacity.
HVAC Equipment
Fans, pumps, and chillers are cataloged in horsepower, kW, or tons of refrigeration. Designers convert to the unit used on the project schedule.
Automotive and Marine
Engine output is advertised in horsepower in some markets and kilowatts in others. Comparing vehicles requires a consistent power unit.
Renewable Energy
Inverter and turbine ratings are in kW or MW while some legacy documents still use horsepower. Conversion keeps interconnection studies consistent.
Workshop and Tooling
Machine-tool spindles and air compressors are often labeled in horsepower. Electrical planning converts that rating to kW for feeder and breaker sizing.
Watt to Horsepower FAQs
Common questions about converting watt to horsepower.
How many watts are in 1 horsepower?
Mechanical: 745.699872 W. Electrical: 746 W exactly. Metric: 735.49875 W. If a source does not name the convention, assume mechanical hp in US engine work and metric hp on European vehicle papers. This calculator assumes mechanical hp.
Why do 746 W and 745.7 W both appear as “1 hp”?
746 W is the electrical-horsepower definition used by NEMA. 745.7 W is 550 ft·lbf/s converted with the international foot and pound-force. They differ by 0.3 W (0.04%). Use 746 when the motor standard says electrical horsepower; use 745.7 for shaft mechanics.
Is metric horsepower the same as mechanical horsepower?
No. Metric horsepower is 1.4% smaller (735.5 W vs 745.7 W). 100 PS = 73.55 kW, while 100 mechanical hp = 74.57 kW. Converting watts with the wrong divisor mis-sizes a generator or a dyno correction.
Can I convert watts to horsepower for an AC motor without efficiency?
You can convert nameplate output watts (or kW) to hp. You cannot convert supply watts to output hp without efficiency and, for AC, power factor if you only have VA. Output hp ≈ (V × I × PF × η × √3) / 746 for a three-phase motor — that is an electrical sizing identity, not a unit change.
What is 1 000 watts in horsepower?
1 000 W = 1.3410 mechanical hp = 1.3405 electrical hp = 1.3596 metric hp. The table on this page lists more input watts using the mechanical definition.
Does this page convert kilowatts or horsepower-hours?
Watts and horsepower are both power. For kilowatts use the horsepower-to-kilowatts converter (or divide watts by 1 000 first). Horsepower-hour is energy and is not interchangeable with watts.
Charts and printable PDF
Use the matching watt / horsepower chart when you need a printable table or offline reference.
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