Power Converter
Convert between watts, horsepower (mechanical, electric, metric), BTU per hour, and more. Free online power unit converter for engines and appliances.
The power value you want to convert
The power unit you are converting from
The power unit you are converting to
Results
Result (W → hp)
1 W = 0.0013410221 hp
- Formula
- 1 × (1 ÷ 745.69987) = 0.0013410221
The formula
result = value × (factor_from ÷ factor_to)
- P
- Power
- 1 W & 1 kW
- SI Power Units (Watt & Kilowatt)
- 1 hp (Mechanical)
- One Mechanical Horsepower
Worked example — Value to Convert 1
Result (W → hp) = 1 W = 0.0013410221 hp
How Power Converter Works
result = value × (factor_from ÷ factor_to)
Power conversion uses linear factors relative to the Watt (W), the SI base unit of power named after the Scottish engineer James Watt. One watt equals one joule per second. Different horsepower variants reflect historical measurement standards — mechanical horsepower (745.7 W) was defined by James Watt in the 1780s to market his improved steam engines by comparing them to draft horses turning mill wheels. Electrical horsepower (746 W) is the standard for electric motor nameplate ratings.
Metric horsepower (735.5 W, also called PS or CV) is the European and Japanese automotive standard, defined as the power to lift 75 kg one meter in one second. For converting between these units, multiply the value by the from-unit factor and divide by the to-unit factor.
- P
- Power — The rate at which energy is transferred or converted, measured in watts (W) or horsepower (hp). One watt equals one joule per second. Power = Energy ÷ Time — a 100 W bulb uses 100 joules of electrical energy every second. In mechanical terms, power = force × velocity for linear motion, or torque × angular velocity for rotation.
- 1 W & 1 kW
- SI Power Units (Watt & Kilowatt) — Watt: one joule per second. A typical LED bulb uses 10 W, a laptop uses 30-100 W. Kilowatt (1,000 W): the standard unit for electrical appliance ratings, EV motor output, and solar panel capacity. 1 hp is approximately 0.746 kW. A typical household consumes 1-2 kW averaged over a day.
- 1 hp (Mechanical)
- One Mechanical Horsepower — 745.7 watts, defined by James Watt as the sustained power of a draft horse. The standard rating for US vehicle engines and industrial equipment. 1 hp = 550 ft·lbf/s, meaning it can lift 550 pounds one foot in one second. A typical family sedan produces 150-200 hp, while a Formula 1 car produces over 1,000 hp from a 1.6L engine.
Source: The watt (W) was named after James Watt (1736-1819) and adopted as the SI unit of power by the 11th CGPM (General Conference on Weights and Measures) in 1960. Horsepower was defined empirically by James Watt in the 1780s through experiments with draft horses turning mill wheels. Watt calculated that a horse could lift 33,000 pounds one foot in one minute, establishing 1 hp = 550 ft·lbf/s = 745.69987158227022 W exactly. The BTU (British Thermal Unit) was defined as the heat energy required to raise one pound of water by one degree Fahrenheit, with 1 BTU/h = 0.29307107 W adopted by the International Steam Table Conference of 1929.
Worked Examples
An automotive journalist in Stuttgart is reviewing a European-spec BMW i4 M50 that is rated at 400 kW. American readers want to know the mechanical horsepower. Convert 400 kW to mechanical horsepower and metric horsepower.
value = 400 · from = kw · to = hp
400 kW = 400,000 W. Mechanical hp: 400,000 ÷ 745.7 = 536.4 hp. Metric hp (PS): 400,000 ÷ 735.5 = 543.9 PS. Quick mental check: 400 × 1.341 = 536.4 hp — matches.
European car marketing often quotes PS (metric horsepower) because the number is about 1.4% higher than mechanical horsepower, making the car look slightly more powerful. A car rated at 300 PS is actually 296 mechanical hp. The kW rating is the only unambiguous number — always check the kW figure if available, then convert to your preferred unit. For metric: 400 × 1.36 = 544 PS — close enough for casual comparison. The difference between mechanical and metric horsepower (536 vs 544) is about 1.5%, which matters for racing classes with strict power limits but is negligible for everyday car comparisons.
An HVAC contractor in Phoenix is selecting a window air conditioner for a 400 sq ft master bedroom. Based on Manual J load calculations, the room needs 5,800 BTU/h of cooling capacity. The store lists units in watts (common for imported units). What wattage rating is needed?
value = 5800 · from = btuh · to = w
5,800 BTU/h × 0.293071 = 1,699.8 W. Round up to 1,700 W. A unit labeled 1,700 W is equivalent to a 5,800 BTU/h unit. Select a 6,000 BTU/h (~1,760 W) unit for safety margin in Phoenix summers exceeding 110°F.
The BTU/h unit persists in North American HVAC despite global metrication because the industry is built around this unit. The "ton of refrigeration" (12,000 BTU/h = 3.517 kW) dates back to the ice harvesting era when cooling was measured by how many tons of ice melted per day. This historical artifact remains the standard unit in HVAC load calculation software and equipment catalogs throughout the United States and Canada. Standard residential window AC units typically come in sizes like 5,000, 6,000, 8,000, 10,000, and 12,000 BTU/h.
A factory manager in Ohio is replacing a 40 hp electric motor that drives a conveyor system. The new motor from a German supplier is rated in kW. Determine the equivalent kW rating, and verify the electrical supply can handle the starting current.
value = 40 · from = hpe · to = kw
40 hp(electric) × 746 W/hp = 29,840 W = 29.84 kW. With 1.15 service factor: 29.84 × 1.15 = 34.3 kW. Select a 37 kW motor (the next standard IEC frame size above 30 kW). Always round up to the next standard size.
Electric motors follow standardized frame sizes — NEMA in North America, IEC internationally. The service factor (SF) accounts for temporary overloads and voltage variations. A motor with SF = 1.15 can operate at 115% of rated load continuously without overheating. For the electrical supply: a 37 kW motor at 480V three-phase draws approximately 56 amps running current, but starting (inrush) current can be 300-400 amps for 2-6 seconds. The circuit breaker and wiring must be sized for this inrush, not just the running current. IEC standard motor ratings are: 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55, 75, 90, 110, 132, 160, 200, 250, 315 kW.
Understanding the Result
Power measures how quickly work is done — the rate of energy transfer per unit time. The concept was formalized during the Industrial Revolution when James Watt (1736-1819), a Scottish engineer, needed a way to compare the output of his improved steam engines to the work of draft horses. Watt conducted experiments in the 1780s, measuring how much weight a horse could lift over time. He calculated that a typical draft horse could perform 33,000 foot-pounds of work per minute, which he defined as one horsepower — a brilliant marketing innovation that allowed him to tell mill owners exactly how many horses his engine could replace.
The watt (W) was later named in his honor and adopted as the SI unit of power by the 11th General Conference on Weights and Measures (CGPM) in 1960. One watt equals one joule of energy transferred per second. Today, power ratings appear everywhere in modern life: vehicle engines (150-400 hp or 110-300 kW), household appliances (800-1,500 W for a microwave), HVAC systems (12,000-60,000 BTU/h for residential air conditioning), and industrial machinery (megawatts for power plants and factory motors).
Electric vehicles rate their motors in kW — a Tesla Model 3 Performance produces roughly 340 kW (approximately 460 hp), while a Lucid Air Sapphire delivers over 900 kW (approximately 1,200 hp). Understanding power conversion helps compare equipment across regions and industries: European car specifications use kW, American specs use mechanical horsepower, Japanese specs may use PS (metric horsepower), HVAC equipment in North America uses BTU/h, and solar panels are universally rated in watts.
This converter bridges all common power units for engineers, technicians, tradespeople, and consumers.
How to Use
- Enter the power value you want to convert in the "Value" field (e.g., 300 for 300 hp or 5 for 5 kW).
- Select the current power unit from the "From" dropdown — choose from watts, horsepower variants, BTU/h, and more.
- Select the desired power unit from the "To" dropdown — the unit you need for your application or comparison.
- The converted value appears instantly with the formula breakdown. Use this to compare car engine specs across regions, size electrical equipment, or convert HVAC ratings.
- Check the worked examples below for real-world scenarios like converting European car specs to American horsepower or sizing an air conditioner.
Quick Reference
| 1 hp (mechanical) | 745.7 W / 0.746 kW |
| 1 kW | 1.341 hp / 3,412 BTU/h |
| 1 hp (metric) | 735.5 W / 0.735 kW |
| 1 hp (electric) | 746 W / 0.746 kW |
| 1 BTU/h | 0.293 W |
| 1 MW | 1,341 hp / 1,000 kW |
| 1 ft·lbf/s | 1.356 W |
| 1 kcal/s | 4,184 W / 4.184 kW |
Frequently Asked Questions
- What is the difference between horsepower and watt?
- A watt is the SI unit of power: 1 W equals 1 joule per second. Horsepower is a larger imperial unit: 1 mechanical hp equals 745.7 W. James Watt defined horsepower as the sustained power of a draft horse turning a mill wheel — about 33,000 foot-pounds per minute. For quick everyday conversion: divide hp by 1.34 to get kW, or multiply kW by 1.34 to get hp. A 200 hp car engine produces about 149 kW. Modern EV motors are typically rated in kW directly.
- Why are there three different horsepower units?
- Mechanical horsepower (745.7 W) is the original James Watt standard, used for US vehicle engines and industrial equipment. It equals 550 foot-pounds per second — the power to lift 550 pounds one foot in one second. Electrical horsepower (746 W exactly) was defined later for electric motor nameplate ratings, choosing 746 as a round number close to 745.7 for simpler motor calculations. Metric horsepower (735.5 W, also called PS in German, CV in French/Italian, ch in French) is the European and Japanese standard, defined as the power to lift 75 kilograms one meter in one second against standard gravity. The differences are historical and regional. A car rated at 300 PS (metric) is only 296 hp (mechanical) — a 1.4% difference that matters for racing regulations with strict power limits but is negligible for everyday driving.
- How do I convert engine power between hp and kW?
- To convert mechanical horsepower to kilowatts: multiply by 0.7457. For kW to hp: divide by 0.7457. Example: 300 hp × 0.7457 = 223.7 kW. Example: 150 kW ÷ 0.7457 = 201 hp. For quick mental estimates, divide hp by 1.34 or multiply kW by 1.34 — the error is under 0.1%, accurate enough for any practical purpose. European vehicle specifications use kW because it is the SI standard, but horsepower remains the dominant marketing number globally. Most modern car specification sheets list both figures. For electric vehicles, kW is the native rating since battery power and motor output are directly measured in electrical kilowatts.
- What is the power consumption of common household appliances?
- Typical power draws at 120V: LED light bulb (8-15 W), ceiling fan (50-75 W), laptop computer (30-100 W), desktop computer with monitor (200-500 W), refrigerator cycling (100-800 W, averaging about 150 W), microwave oven (800-1,500 W), toaster (800-1,500 W), hair dryer (1,200-1,800 W), window air conditioner (800-1,500 W for a small unit), electric water heater (3,000-5,500 W), clothes dryer (2,000-5,000 W), Level 2 EV charger (3,300-7,700 W). A typical home draws 15-30 kW at peak (all major appliances running) but averages 1-2 kW over 24 hours. For monthly operating cost: multiply kW rating × hours used per day × 30 days × your electricity rate in dollars per kWh.
- How do I convert BTU/h to watts for HVAC equipment?
- 1 BTU/h equals 0.29307107 W. To convert BTU/h to watts: multiply by 0.29307. For watts to BTU/h: divide by 0.29307, or multiply kW by 3,412 to get BTU/h. Common HVAC sizes for reference: a small window unit (5,000 BTU/h ≈ 1,465 W), a medium room unit (12,000 BTU/h ≈ 3,516 W or 3.5 kW), a small central AC (24,000 BTU/h ≈ 7 kW), a whole-house central AC (36,000-60,000 BTU/h ≈ 10.5-17.6 kW). The "ton" of refrigeration (12,000 BTU/h = 3.517 kW) comes from the cooling power of melting one ton (2,000 lbs) of ice at 32°F over 24 hours. This pre-electricity measurement standard persists in North American HVAC specifications to this day.
- How much power does an electric vehicle use compared to a gasoline car?
- A typical EV motor produces 150-300 kW (200-400 hp), similar to gasoline cars in peak power output. However, EVs are 85-95% efficient at converting stored electrical energy to wheel motion, versus only 20-30% for gasoline engines (the remaining 70-80% is lost as heat through the radiator and exhaust). This means a 75 kWh battery pack holds the chemical-energy equivalent of only about 2.2 gallons of gasoline (75 ÷ 33.7 kWh per gallon) yet drives roughly 250-300 miles, because far more of that energy reaches the wheels. At 70 mph a typical EV draws about 20-25 kW from its battery.
Common Uses
- •Comparing car engine specifications across regions: European automakers rate engines in kW (or metric horsepower as PS), while American and British specs use mechanical horsepower. A BMW rated at 250 kW produces approximately 335 hp. The Tesla Model S Plaid produces 760 kW (1,020 hp).
- •Selecting electric motors for industrial machinery: motor nameplates show power in hp(electric) or kW. A 40 hp motor is rated at about 29.8 kW of shaft output. Converting between these ensures the motor meets the load requirement with proper safety margin (typically 1.15-1.25 service factor for continuous duty).
- •Sizing HVAC equipment: air conditioners are rated in BTU/h in North America but in kW elsewhere. A 12,000 BTU/h unit equals approximately 3.5 kW of cooling capacity. The "ton" in HVAC (1 ton = 12,000 BTU/h) comes from the cooling power of melting one ton of ice over 24 hours.
- •Evaluating solar panel arrays: panels are rated in watts peak (Wp) under standard test conditions, while inverters and battery storage are rated in kW. A 10 kW residential solar system with 400 W panels requires 25 panels. Real-world output is typically 75-85% of rated capacity due to temperature, inverter efficiency, and wiring losses.
- •Calculating generator sizing: backup generators are rated in kW or kVA. Motor starting current (inrush) is typically 3-7 times the running current, so a 5 hp motor (3.73 kW running) may need 15-20 kW of generator capacity to start. Always convert all loads to a common unit before summing.
- •Data center power budgeting: server racks are rated in kW, but total facility power includes cooling overhead (PUE — Power Usage Effectiveness). A 10 kW rack load typically requires 14-20 kW of total facility power (PUE of 1.4-2.0). Budget cooling separately from IT equipment power.
Pro Tips
- →When comparing vehicle specs, always check which horsepower standard is being used. A car rated at 300 PS (metric hp) is actually 296 mechanical hp — close enough for casual comparison, but the difference matters in racing classes with power limits. The kW figure is the only unambiguous specification.
- →For electrical appliances: 1 kW running continuously for 24 hours costs about $2.40-$3.10 per day at average US electricity rates ($0.10-$0.13/kWh). A 1,500 W space heater costs roughly $3.60-$4.70 per 24 hours. Use this rule of thumb to quickly estimate operating costs: dollars per day ≈ kW × 24 × your electric rate.
- →BTU/h to kW mental shortcut: divide BTU/h by 3,412. For most HVAC estimates, dividing by 3,400 gives a close enough answer with less than 0.4% error. Example: 36,000 BTU/h ÷ 3,400 ≈ 10.6 kW (actual: 36,000 × 0.293071 / 1000 = 10.55 kW). This shortcut is accurate enough for sizing electrical circuits and comparing equipment.
- →Data center power: server racks are rated in kW, but total facility power includes cooling overhead. A 10 kW rack load typically requires 14-20 kW of total facility power (PUE of 1.4-2.0). Modern hyperscale data centers achieve PUE of 1.1-1.2. Always budget cooling separately when converting server specs to facility electrical requirements.
- →Solar panel math: a standard residential panel produces 350-450 W under ideal Standard Test Conditions (STC: 1000 W/m² irradiance, 25°C cell temperature). In the real world, account for 75-85% derating (inverter efficiency, wiring losses, temperature degradation, soiling). A 10 kW DC array produces roughly 7.5-8.5 kW AC at the inverter output. Use the NOCT (Normal Operating Cell Temperature) rating for realistic estimates.
- →For generator sizing: motor starting current (inrush) is typically 3-7 times the running current. A 5 hp motor (3.73 kW running) may need 15-20 kW of generator capacity to start. Always convert motor loads to starting kVA (not just running kW) when sizing generators, and account for the sequence in which loads start — simultaneous motor starts demand far more capacity than sequential starts.
Limitations to Know
- •When not to rely on conversion alone: This calculator performs linear unit conversion only. It does not account for efficiency losses — a motor rated at 10 kW output power draws more than 10 kW of electrical input, typically 10-15% more for induction motors depending on efficiency class (IE3 premium efficiency motors lose about 5-7%).
- •Horsepower ratings for engines vary by testing standard: SAE net (as-installed with all accessories, air filter, exhaust), SAE gross (bare engine, no accessories, typically 15-20% higher), DIN (European, similar to SAE net), and JIS (Japanese). This calculator converts units, not rating standards — 300 SAE net hp and 300 DIN hp may represent different actual engine outputs despite the same numerical value.
- •BTU/h ratings for HVAC equipment vary by operating conditions. AHRI standard rating conditions (95°F outdoor, 80°F indoor dry bulb, 67°F wet bulb) produce rated capacity, but actual capacity decreases as outdoor temperature rises. A 12,000 BTU/h unit at 95°F may only deliver 10,500 BTU/h at 110°F outdoor temperature — a 12.5% capacity loss.
- •Power (rate of energy use) is different from energy (total consumption). 1 kW sustained for 1 hour equals 1 kWh of energy. This calculator converts power units, not energy units. For energy conversion (kWh to BTU, joules, therms, etc.), use an energy converter. Confusing kW and kWh is one of the most common mistakes in electrical calculations.
- •For electrical systems, apparent power (kVA) differs from real power (kW) by the power factor (PF). Motors typically have PF of 0.8-0.9 lagging, meaning a 10 kW motor draws 11.1-12.5 kVA from the supply. This calculator converts real power units (W, kW, hp, BTU/h). For kVA conversion, divide kW by the power factor: kVA = kW ÷ PF.
Cite this calculator
TheCalcUniverse. "Power Converter — Watts, Horsepower, BTU/h & More." TheCalcUniverse, 2026, https://thecalcuniverse.com/industrial/power-converter/. Accessed October 25, 2026.
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