Horsepower to Watts (hp to W)
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Mechanical-horsepower-to-watts conversions translate US-customary engine, motor, pump, and powertrain power figures from the hp primary into the SI watt used for international engineering documentation, ISO-and-EN compliance, and physics-engineering work. A 200 hp engine output translates to 149,140 W or 149 kW for international SI vehicle-engineering documentation; a 100 hp electric-motor rating translates to 74,570 W or 74.6 kW for ISO-and-IEC industrial-motor documentation; a 50 hp pump-motor translates to 37,285 W or 37.3 kW for international pump-engineering documentation. The factor is exact at 1 hp = 745.6998715822702 W, derived from the mechanical horsepower definition (550 ft·lbf/s) via the foot-and-pound-and-second conversion factors that are themselves exact under the 1959 international yard-and-pound agreement.
How to convert Horsepower to Watts
Formula
W = hp × 745.6999
To convert mechanical horsepower to watts, multiply the hp figure by 745.6999 — the factor exact at 745.6998715822702 W per hp. The factor is fixed by the mechanical horsepower definition (550 ft·lbf/s) via the foot-and-pound-and-second conversion factors that are themselves exact under the 1959 international yard-and-pound agreement. For mental math, "hp × 0.746" gives kW directly: 1 hp ≈ 0.746 kW, 100 hp ≈ 74.6 kW, 200 hp ≈ 149 kW, 500 hp ≈ 373 kW, 1000 hp ≈ 746 kW. The conversion runs at every US-customary-hp source to international-SI-W destination boundary across vehicle-engineering, industrial-motor, pump-engineering, and aviation-engineering documentation work in cross-international engineering practice.
Worked examples
Example 1 — 1 hp
One mechanical horsepower equals exactly 745.6998715822702 watts, derived from the mechanical horsepower definition (550 ft·lbf/s) via the foot-and-pound-and-second conversion factors fixed by the 1959 international yard-and-pound agreement. The factor is exact rather than measured.
Example 2 — 200 hp
Two hundred mechanical horsepower — a typical mid-size sedan engine output — converts to 149,140 W or 149 kW on the international SI vehicle-engineering documentation. The hp-figure is the US-customary SAE primary; the kW-figure is the international SI vehicle-engineering reference.
Example 3 — 100 hp
One hundred mechanical horsepower — a typical industrial electric-motor rating — converts to 74,570 W or 74.6 kW on the ISO-and-IEC industrial-motor documentation. The hp-figure is the US-customary NEMA primary; the kW-figure is the international IEC-60034 reference.
hp to W conversion table
| hp | W |
|---|---|
| 1 hp | 745.6999 W |
| 2 hp | 1491.3997 W |
| 3 hp | 2237.0996 W |
| 4 hp | 2982.7995 W |
| 5 hp | 3728.4994 W |
| 6 hp | 4474.1992 W |
| 7 hp | 5219.8991 W |
| 8 hp | 5965.599 W |
| 9 hp | 6711.2988 W |
| 10 hp | 7456.9987 W |
| 15 hp | 11185.4981 W |
| 20 hp | 14913.9974 W |
| 25 hp | 18642.4968 W |
| 30 hp | 22370.9961 W |
| 40 hp | 29827.9949 W |
| 50 hp | 37284.9936 W |
| 75 hp | 55927.4904 W |
| 100 hp | 74569.9872 W |
| 150 hp | 111854.9807 W |
| 200 hp | 149139.9743 W |
| 250 hp | 186424.9679 W |
| 500 hp | 372849.9358 W |
| 750 hp | 559274.9037 W |
| 1000 hp | 745699.8716 W |
| 2500 hp | 1864249.679 W |
| 5000 hp | 3728499.3579 W |
Common hp to W conversions
- 1 hp=745.6999 W
- 5 hp=3728.4994 W
- 10 hp=7456.9987 W
- 25 hp=18642.4968 W
- 50 hp=37284.9936 W
- 100 hp=74569.9872 W
- 200 hp=149139.9743 W
- 500 hp=372849.9358 W
- 1000 hp=745699.8716 W
- 2000 hp=1491399.7432 W
What is a Horsepower?
The horsepower (hp) under the US-customary mechanical-horsepower definition is exactly 745.69987158227022 W (typically rounded to 745.7 W). The metric horsepower (PS, sometimes "hp" in continental European contexts) is exactly 735.49875 W — about 1.4% smaller than the mechanical hp. The recognised symbols are "hp" (mechanical, US-customary) and "PS" or "ch" (metric, continental European), with both widely used and the disambiguation context-dependent. The horsepower is not part of the SI but is recognised by NIST as a US-customary power unit accepted for limited use, with ISO 80000-6 deprecating it in favour of kilowatts for new technical writing. The horsepower persists in US-customary automotive engine specs (every US-domestic car, truck, and motorcycle specifies engine power in hp), continental European automotive specs in PS for the consumer-recognition reference alongside kW regulatory primary, and a number of US-customary industrial-engineering legacy contexts.
The horsepower was defined by James Watt around 1782 to market his improved steam engines against the existing horse-powered industrial machinery they replaced. Watt observed that draft horses lifting coal from a Cornish mine could sustain about 22,000 foot-pounds per minute over a working day, rounded up to 33,000 foot-pounds per minute (550 foot-pounds per second) as the convenient marketing-friendly figure that would let buyers compare steam-engine output directly against horse-team capacity. The unit became the dominant power-rating convention for steam engines, internal-combustion engines, and US-customary engineering work through the nineteenth and twentieth centuries. Multiple slightly-different "horsepower" definitions emerged: the mechanical horsepower (US-imperial) at exactly 745.7 W, the metric horsepower (PS, "Pferdestärke" in German) at exactly 735.49875 W, the boiler horsepower (US-engineering) at 9809.5 W, and the electrical horsepower at 746 W (approximately equal to mechanical hp). The "hp" symbol typically refers to the mechanical horsepower in US contexts and the metric horsepower in continental European automotive specs. ISO 80000-6 deprecates horsepower in favour of kilowatts for new technical writing, but US-customary automotive and industrial-engine specs preserve it.
US-customary automotive engine power specs: every US-domestic car, truck, motorcycle, and ATV specifies engine power in horsepower on the manufacturer-spec sheet, advertising materials, and EPA-fuel-economy disclosures. Typical US passenger-car engine 150-300 hp; typical US light-truck 250-400 hp; typical US sports-car 400-700 hp; supercars 700-1000 hp. The horsepower-rating is the primary consumer-comparison metric for US-customary automotive marketing. Continental European automotive PS specs: European-manufactured cars (Volkswagen, BMW, Mercedes-Benz, Porsche, Ferrari, Lamborghini) preserve the metric horsepower (PS) on European-domestic-market spec sheets alongside kW as the regulatory primary under EU vehicle-type-approval rules. A "200 PS" Volkswagen Golf equates to 147 kW or 197 mechanical hp, with the PS-figure as the consumer-recognition reference and the kW-figure as the regulatory primary. US-customary industrial engines and pumps: US-customary industrial engine specs (Caterpillar diesel engines, Cummins generator sets, John Deere agricultural-equipment engines) and industrial pump specs (Goulds Pumps, Grundfos US-distribution) denominate rated power in horsepower for the US-customary engineering primary. A "200 hp diesel engine" delivers 149 kW of rated mechanical output. US-customary boating and small-craft motors: outboard-motor and stern-drive marine engines (Mercury Marine, Yamaha Marine, Honda Marine, Suzuki Marine) specify rated power in horsepower for the US-customary boat-and-small-craft engine sales. A 200 hp outboard motor delivers 149 kW of rated power.
What is a Watt?
The watt (W) is the SI-derived unit of power, equal to one joule of energy delivered per second of time (1 W = 1 J/s = 1 N·m/s = 1 V·A in electrical engineering). The watt is anchored to the SI base units kilogram, metre and second through the relationship 1 W = 1 kg·m²·s⁻³. Since the 2019 SI redefinition the watt is fixed via the Planck constant h = 6.62607015 × 10⁻³⁴ J·s exactly, with the kilogram derived from this anchoring rather than the historical artifact-based definition. The recognised SI symbol is "W" (uppercase, honouring James Watt). Higher-power multiples use kilowatts (kW, 1000 W), megawatts (MW, 10⁶ W) for grid-scale power-generation, and gigawatts (GW, 10⁹ W) for nuclear-power-station and large-scale industrial-power references. The watt is the universal SI power unit and replaces older non-SI power units (horsepower, BTU/h) in modern technical and SI-canonical work.
The watt is named after James Watt (1736-1819), the Scottish engineer whose late-eighteenth-century improvements to the Newcomen steam engine transformed industrial-power generation and made the steam engine the foundational technology of the Industrial Revolution. Watt patented the separate-condenser steam-engine improvement in 1769, the rotative-motion governor in 1788, and the parallel-motion linkage in 1784, with each innovation increasing fuel-efficiency and power-output of industrial steam plants. The unit "watt" was formally adopted by the British Association for the Advancement of Science in 1882 to name the SI-derived power unit equal to one joule per second, with the unit officially incorporated into the SI at the 11th CGPM in 1960. The 2019 SI redefinition fixed the watt via the kilogram-Planck-constant chain through the joule-per-second relationship — a watt is the rate of energy delivery, where one joule of energy is delivered per second. The watt is universally used across electrical engineering, mechanical engineering, electronics, lighting, audio, and consumer-product power-rating contexts globally.
Electrical engineering and consumer-electronics power ratings: every electrical and electronic device denominates power consumption in watts on the consumer-facing rating label and the engineering specification. Typical residential lighting at 5-15 W LED, 60-100 W incandescent (legacy); typical kitchen appliances at 800-3000 W; typical computer power supplies at 350-1500 W; typical residential solar-PV inverters at 3000-10000 W (3-10 kW). EU Ecodesign Directive 2009/125/EC mandates watt-based product power-rating labels on every EU-jurisdiction electrical product. Lighting and LED specs: every modern lighting product (incandescent, halogen, fluorescent, LED) specifies power-consumption rating in watts, with the consumer-facing comparison metric "lumens-per-watt" for energy efficiency. Typical LED bulb 8-15 W replacing 60 W incandescent at 800 lm light output. EU Lamps Directive and US ENERGY STAR criteria use watt-based ratings. Audio amplifier and home-theatre power output: home-theatre AV-receivers, hi-fi amplifiers, car-audio systems all specify power-output in watts (typical home-theatre 100-200 W per channel, hi-fi 50-300 W per channel, car-audio 50-400 W per channel). Consumer-comparison shopping uses watt-based RMS output ratings. Solar-PV and wind-turbine generation: residential solar-PV system capacity in W (3-10 kW typical residential, 100-500 kW commercial), wind-turbine rated power in W (typical residential micro-wind 1-10 kW, utility-scale 2-15 MW per turbine).
Real-world uses for Horsepower to Watts
US-customary hp engine-output translated to W for international SI vehicle-engineering documentation
US-customary hp engine-output specifications under SAE J-standard conventions translate to W for international SI vehicle-engineering documentation under UN ECE WP.29 vehicle-regulation conventions when US-market vehicles are exported to international markets, or when international-vehicle-engineering programs require SI documentation. A 200 hp engine translates to 149.1 kW; a 600 hp performance-engine translates to 447.4 kW; a 1000 hp supercar-engine translates to 745.7 kW. The conversion runs at every SAE-hp source to UN-ECE-W vehicle-engineering documentation step in cross-international automotive programs.
US-customary hp electric-motor-rating translated to W for ISO-and-IEC industrial-motor documentation
US-customary hp electric-motor ratings under NEMA conventions translate to W for ISO-and-IEC industrial-motor documentation under IEC 60034 motor-rating conventions when US-market motors are exported or international-equipment-installation requires SI documentation. A 100 hp standard motor translates to 74.6 kW; a 250 hp large-industrial-motor translates to 186.4 kW; a 1000 hp utility-scale-motor translates to 745.7 kW. The conversion runs at every NEMA-hp source to IEC-60034-W motor-documentation step in international industrial-equipment programs.
US-customary hp pump-motor translated to W for international pump-engineering documentation
US-customary hp pump-motor specifications under HI (Hydraulic Institute) conventions translate to W for international pump-engineering documentation under EN-and-ISO pump-engineering conventions. A 50 hp pump-motor translates to 37.3 kW; a 200 hp HVAC-circulation-pump translates to 149.1 kW; a 500 hp wastewater-pump translates to 372.9 kW; a 25 hp residential-well-pump translates to 18.6 kW. The conversion runs at every HI-hp source to EN-and-ISO pump-engineering-W documentation step in international pump-equipment programs.
US-customary hp aircraft-engine translated to W for international ICAO-and-EASA aviation-engineering documentation
US-customary hp piston-aircraft-engine specifications under FAA conventions translate to W for international ICAO-and-EASA aviation-engineering documentation when general-aviation-and-business-jet aircraft are operated internationally or imported to international markets. A 180 hp Cessna-172-engine translates to 134.2 kW; a 300 hp Cirrus-SR22-engine translates to 223.7 kW; a 1700 hp WWII-warbird-engine translates to 1267.7 kW or 1.27 MW. The conversion runs at every FAA-hp source to ICAO-EASA-W aviation-engineering documentation step in cross-international general-aviation programs.
When to use Watts instead of Horsepower
Use watts whenever the destination is international SI engineering documentation under ISO-and-IEC-and-EN-and-EASA conventions, UN ECE WP.29 vehicle-engineering, IEC 60034 motor-rating, EN-and-ISO pump-engineering, ICAO-and-EASA aviation-engineering, or any international-engineering context where W or kW is the standard reference unit. The watt-figure is the universal SI-derived power unit, with kW used at industrial-motor-and-vehicle scale and MW at utility-power-plant scale. Stay in mechanical horsepower when the destination is US-customary engineering documentation under SAE-and-NEMA-and-HI conventions, FAA general-aviation aircraft-engine specifications, US-bound consumer-vehicle marketing, or any US-customary context where hp-scale granularity matches everyday US-convention power intuition. The conversion is the universal US-customary-to-SI power scale-shift between hp-source and W-destination documentation, applied across vehicle-engineering, industrial-motor, pump-engineering, and aviation-engineering work in cross-international engineering practice.
Common mistakes converting hp to W
- Confusing mechanical horsepower (745.6999 W, the standard automotive-and-mechanical-engineering hp) with metric horsepower (PS or ch, 735.499 W, used in continental-European automotive documentation), boiler horsepower (9809.5 W, used in steam-boiler engineering), and electrical horsepower (746 W, used in some legacy US electrical-engineering documentation). The four hp variants differ by up to 1.3% — always verify which hp variant the source figure uses.
- Treating "1 hp = 1 kW" as a rough equivalence. The two units differ by a factor of about 0.746 (kW per hp), and substituting one for the other gives a 25-34% power-magnitude error. The correct factor is 1 hp = 0.7457 kW exactly under the mechanical horsepower convention.
Frequently asked questions
How many watts in 1 hp?
One mechanical horsepower equals exactly 745.6999 watts, derived from the mechanical horsepower definition (550 ft·lbf/s) via the foot-and-pound-and-second conversion factors fixed by the 1959 international yard-and-pound agreement. The factor is exact rather than measured. The "1 hp ≈ 745.7 W" or "1 hp ≈ 0.7457 kW" reference is universal in modern US-customary-to-SI power conversion across vehicle-engineering, industrial-motor, pump-engineering, and aviation-engineering work.
How many watts in 200 hp (mid-size engine)?
Two hundred mechanical horsepower equals 149,140 watts or 149 kW. That is a typical mid-size-sedan engine output translated to international SI vehicle-engineering documentation. The hp-figure sits on the US-customary SAE primary specification and the kW-figure sits on the international SI vehicle-engineering reference under UN ECE WP.29 conventions for cross-international vehicle programs.
How many watts in 100 hp (industrial motor)?
One hundred mechanical horsepower equals 74,570 watts or 74.6 kW. That is a typical industrial electric-motor rating translated to ISO-and-IEC industrial-motor documentation. The hp-figure sits on the US-customary NEMA primary specification and the kW-figure sits on the international IEC 60034 motor-rating reference for international equipment-installation programs.
Quick way to convert hp to watts in my head?
Multiply the hp figure by 0.746 to get kW directly (or by 746 for W). For 1 hp that gives 0.746 kW or 746 W, for 100 hp that gives 74.6 kW, for 200 hp that gives 149 kW, for 500 hp that gives 373 kW, for 1000 hp that gives 746 kW. The exact factor is 0.7457 kW per hp, with the rounded "× 0.746" approximation within 0.04% of exact for everyday power-conversion work.
How many hp in 1 watt?
One watt equals about 0.001341 hp, the multiplicative inverse of 745.6999 W per hp. The factor is exact under the mechanical horsepower definition. The "1 W ≈ 0.00134 hp" reference appears at the inverse-conversion direction when SI engineering W figures are translated back to US-customary hp notation.
When does hp-to-watts conversion appear in real work?
It appears in US-customary hp engine-output translated to W for international SI vehicle-engineering documentation and in US-customary hp electric-motor-rating translated to W for ISO-and-IEC industrial-motor documentation. It also appears in US-customary hp pump-motor translated to W for international pump-engineering documentation and in US-customary hp aircraft-engine translated to W for international ICAO-and-EASA aviation-engineering documentation. The conversion is one of the most-run US-customary-to-SI power conversions globally.
How precise should hp-to-watts be for engineering work?
For engineering work the hp-to-watts conversion is exact (factor 745.6998715822702 exactly under the mechanical horsepower definition), and the precision allowance comes from the underlying source-measurement precision rather than the conversion itself. Most engineering documentation rounds to 4 significant figures (1 hp ≈ 745.7 W or 0.7457 kW), which is sufficient for typical vehicle, industrial, pump, and aviation applications. Always verify which hp variant the source uses (mechanical, metric, boiler, electrical) before applying the factor.