Power Converter
Convert power between watts, kilowatts, horsepower, BTU/hour, and 45+ units. Used in electrical engineering, automotive performance, HVAC sizing, and appliance ratings. See also our HP to kW and Watts to HP converters.
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What is a Power Converter?
A power converter is a tool that converts measurements between different units of power such as watts, kilowatts, horsepower, and BTU per hour. It is used in electrical engineering, automotive performance, HVAC sizing, and any application where energy output rates need to be compared.
History of Power Measurement
James Watt popularized horsepower in the late 18th century to market his steam engines, defining it as the power to lift 550 pounds by one foot per second. The watt was named in his honor and became the SI unit of power in 1882. The ton of refrigeration was based on the cooling power of melting one ton of ice per day.
About This Power Converter
This power converter supports 45 different units including watt, kilowatt, megawatt, gigawatt, horsepower (mechanical, metric, electric, boiler), calorie/second, joule/second, volt ampere, and more. It covers electrical, mechanical, and thermal power systems.
Understanding Power Measurement and Conversion
Power is the rate at which energy is transferred or converted — it tells you how quickly work is being done. A 100-watt light bulb converts 100 joules of electrical energy into light and heat every second. Whether you are sizing an engine, selecting a motor, or comparing appliance efficiency, understanding power units and their relationships is essential. The SI unit of power is the watt (W), named after James Watt, but many industries still rely on horsepower, BTU per hour, or kilocalories per hour.
The confusion around power units arises because different engineering traditions developed independently. Mechanical engineers use horsepower (defined differently in different countries), electrical engineers use watts and kilowatts, HVAC professionals use BTU/hour or tons of refrigeration, and boiler engineers use boiler horsepower. All of these measure the same physical quantity — energy per unit time — but with different scaling factors.
Converting between power units is straightforward once you know the key relationships. The watt serves as the universal bridge: every other power unit can be expressed as some number of watts. This makes the watt the ideal intermediate unit when converting between, say, horsepower and BTU per hour.
How to Convert Between Power Units (Step-by-Step)
Power conversion follows the same multiply-by-a-factor approach as any unit conversion. The key is knowing (or looking up) the correct conversion factor between your source and target units.
- Identify your source unit (e.g., mechanical horsepower) and target unit (e.g., kilowatts).
- Find the conversion factor. For example, 1 mechanical horsepower = 745.6999 watts.
- Multiply your value by the factor to get watts (if not already in watts).
- If your target unit is not watts, divide by the target unit's watt equivalent. For example, to get kilowatts, divide watts by 1,000.
- Verify your answer: a horsepower is roughly 746 watts, so 10 HP should be about 7,460 W or 7.46 kW.
Essential Power Conversion Formulas
These conversion factors connect the most commonly used power units. All values are exact or rounded to 6 significant figures:
- 1 watt (W) = 1 joule/second = 1 kg⋅m²/s³
- 1 kilowatt (kW) = 1,000 watts
- 1 megawatt (MW) = 1,000,000 watts
- 1 mechanical horsepower (hp) = 745.700 watts
- 1 metric horsepower (PS) = 735.499 watts
- 1 electrical horsepower = 746 watts (exact)
- 1 BTU/hour = 0.293071 watts
- 1 ton of refrigeration = 3,516.85 watts
Worked Examples — Power Conversions
Example 1: A car engine produces 250 mechanical horsepower. What is that in kilowatts?
Solution:
1 mechanical horsepower = 745.700 watts.
Multiply: 250 × 745.700 = 186,425 watts.
Convert to kilowatts: 186,425 ÷ 1,000 = 186.425 kW.
Answer: 250 HP = 186.4 kW (approximately).
Example 2: An air conditioner is rated at 12,000 BTU/hour. How many watts does it consume?
Solution:
1 BTU/hour = 0.293071 watts.
Multiply: 12,000 × 0.293071 = 3,516.85 watts.
This equals 3.517 kW or 1 ton of refrigeration.
Answer: 12,000 BTU/hr = 3,516.85 W ≈ 3.5 kW (1 ton of cooling).
Example 3: A European car is rated at 150 PS (metric horsepower). What is that in mechanical HP?
Solution:
1 PS = 735.499 watts, 1 mechanical HP = 745.700 watts.
Convert PS to watts: 150 × 735.499 = 110,324.9 W.
Convert watts to mechanical HP: 110,324.9 ÷ 745.700 = 147.9 HP.
Answer: 150 PS = 147.9 mechanical HP (metric HP is about 1.4% less than mechanical HP).
Example 4: A wind turbine generates 2.5 megawatts. How many homes can it power if each uses 1,200 watts average?
Solution:
2.5 MW = 2,500,000 watts.
Divide by average home consumption: 2,500,000 ÷ 1,200 = 2,083 homes.
Answer: 2.5 MW can power approximately 2,083 homes at 1.2 kW average draw.
Example 5: A boiler is rated at 3 boiler horsepower. What is its output in BTU/hour?
Solution:
1 boiler HP = 9,809.5 watts.
3 boiler HP = 3 × 9,809.5 = 29,428.5 watts.
Convert watts to BTU/hr: 29,428.5 ÷ 0.293071 = 100,414 BTU/hr.
Answer: 3 boiler HP = approximately 100,414 BTU/hr.
Quick Reference — Common Power Conversions
Use this table for fast lookup of common power unit equivalencies.
| From | To |
|---|---|
| 1 watt | 3.412 BTU/hr |
| 1 kilowatt | 1.341 HP |
| 1 megawatt | 1,341 HP |
| 1 horsepower (mech) | 745.7 W |
| 1 horsepower (metric/PS) | 735.5 W |
| 1 horsepower (electric) | 746 W |
| 1 horsepower (boiler) | 9,809.5 W |
| 1 BTU/hour | 0.2931 W |
| 1 ton of refrigeration | 3,516.85 W |
| 1 kilocalorie/hour | 1.163 W |
| 1 foot-pound/second | 1.3558 W |
| 1 gigawatt | 1,000 MW |
| 1 milliwatt | 0.001 W |
| 1 erg/second | 0.0000001 W |
Understanding Power Measurement Systems
The SI system defines power in watts, derived directly from the base units: 1 watt = 1 kilogram × meter² / second³ = 1 joule per second. This clean derivation means watts integrate seamlessly with other SI quantities. Electrical power in watts equals voltage × current (P = V × I). Mechanical power in watts equals force × velocity (P = F × v). The watt is truly universal.
The horsepower originated with James Watt himself, who needed to market his steam engines to mine owners using horse-drawn equipment. He defined it as 550 foot-pounds per second — roughly the sustained output of a strong draft horse. This practical origin means horsepower remains intuitive for engines and motors. However, the metric horsepower (PS, from German Pferdestärke) was later defined as 75 kilogram-force × meters per second, giving a slightly different value (735.5 W vs 745.7 W).
In the HVAC and refrigeration industry, the BTU per hour and ton of refrigeration are standard. One BTU is the energy to raise one pound of water by one degree Fahrenheit, so BTU/hr measures the rate of heating or cooling. One ton of refrigeration (12,000 BTU/hr) represents the cooling power of melting one short ton of ice in 24 hours — a holdover from the ice trade era.
Where Power Conversion Matters
Automotive Engineering
Car specifications list power in HP (USA), PS (Europe), or kW (Australia, EU regulations). Comparing vehicles across markets requires converting between these units. A 200 kW car is approximately 268 HP or 272 PS.
Electrical Systems
Home electrical panels are rated in amps at a given voltage, giving watts. Appliances list wattage on their labels. Understanding that a 1,500 W space heater on a 120V circuit draws 12.5 amps helps avoid tripping breakers.
HVAC & Refrigeration
Air conditioning capacity is rated in BTU/hr or tons in the US, but kilowatts in most other countries. A 3-ton AC system equals 36,000 BTU/hr or about 10.55 kW of cooling capacity.
Renewable Energy
Solar panels are rated in watts peak (Wp), wind turbines in megawatts. Grid-scale storage discusses megawatt-hours. Comparing energy sources requires fluency in power unit conversion.
Industrial Motors
Electric motors are specified in HP in the US and kW elsewhere. A 50 HP motor is approximately 37.3 kW. Motor efficiency ratings affect the actual electrical input required.
Fitness & Cycling
Cyclists measure output in watts using power meters. Professional cyclists sustain 300-400 watts, roughly 0.4-0.5 HP. This provides a tangible connection between human effort and mechanical units.
Common Mistakes in Power Conversion
The most dangerous mistake is confusing energy and power. Kilowatts (kW) measure power (rate), while kilowatt-hours (kWh) measure energy (total amount). A 1 kW heater running for 2 hours uses 2 kWh of energy. Another frequent error is using mechanical horsepower (745.7 W) when metric horsepower (735.5 W) is intended — this 1.4% difference matters in precise engineering. Finally, BTU/hr is often written as just "BTU" in HVAC contexts, which confuses the energy unit (BTU) with the power unit (BTU/hr).
Power vs Torque in Engines
Engine power and torque are related but distinct. Torque (measured in Newton-meters or foot-pounds) is rotational force; power is torque multiplied by rotational speed. The formula is: Power (watts) = Torque (N⋅m) × Angular velocity (rad/s), or in imperial: HP = Torque (lb⋅ft) × RPM ÷ 5,252. This is why an engine can have high torque at low RPM but relatively low power — and why peak power typically occurs at higher RPM than peak torque.
Key Takeaways
- Power is energy per unit time. The SI unit is the watt (1 W = 1 J/s).
- There are multiple definitions of horsepower: mechanical (745.7 W), metric (735.5 W), electrical (746 W), and boiler (9,809.5 W).
- Use the watt as a bridge unit when converting between any two power units.
- In HVAC: 1 ton of refrigeration = 12,000 BTU/hr = 3,517 W.
- Metric prefixes scale watts simply: mW, W, kW, MW, GW (each ×1,000).
- Always verify which "horsepower" definition is being used before converting.
Metric Conversion Factor Tables for Power Converter
| Units to convert | Multiply By The Number | Convert as Unit |
|---|---|---|
| Watt (W) | 0.001 | Kilowatt (kW) |
| Watt (W) | 0.001341022 | Horsepower (hp) |
| Kilowatt (kW) | 1000 | Watt (W) |
| Kilowatt (kW) | 1.3410221 | Horsepower (hp) |
| Horsepower (hp) | 745.69987 | Watt (W) |
| Horsepower (hp) | 0.7456999 | Kilowatt (kW) |
| Horsepower (metric) | 735.49875 | Watt (W) |
| Megawatt (MW) | 1000 | Kilowatt (kW) |
| Gigawatt (GW) | 1000 | Megawatt (MW) |
| Ton (refrigeration) | 3516.853 | Watt (W) |
| Ton (refrigeration) | 3.516853 | Kilowatt (kW) |
| Joule/second (J/s) | 1 | Watt (W) |
| Kilocalorie/minute | 69.78 | Watt (W) |
| Volt Ampere (VA) | 1 | Watt (W) |
Powerconverters & it's abbreviations
| Unit | Abbreviation | Unit | Abbreviation | Unit | Abbreviation |
|---|---|---|---|---|---|
| watt | W | kilowatt | kW | megawatt | MW |
| gigawatt | GW | terawatt | TW | petawatt | PW |
| exawatt | EW | milliwatt | mW | microwatt | µW |
| nanowatt | nW | picowatt | pW | femtowatt | fW |
| centiwatt | cW | deciwatt | dW | horsepower (mechanical) | hp |
| horsepower (metric) | PS | horsepower (electric) | hp(E) | horsepower (boiler) | hp(S) |
| pferdestarke | ps | ton (refrigeration) | ton | kilovolt ampere | kVA |
| volt ampere | VA | joule/second | J/s | joule/minute | J/min |
| joule/hour | J/h | MBH | MBH | newton meter/second | N·m/s |
Frequently Asked Questions
How do I convert horsepower to kilowatts?
Multiply horsepower by 0.7457 to get kilowatts. For example, 200 hp = 200 × 0.7457 = 149.14 kW. This uses mechanical (imperial) horsepower.
What is the difference between hp and metric hp?
Mechanical horsepower (hp) equals 745.7 watts. Metric horsepower (PS) equals 735.5 watts. The difference is about 1.4%, with mechanical hp being slightly larger.
How many watts are in a kilowatt?
There are exactly 1,000 watts in one kilowatt. Similarly, 1 megawatt = 1,000 kilowatts = 1,000,000 watts.
What is a ton of refrigeration?
A ton of refrigeration equals 3,516.85 watts (about 3.5 kW). It represents the cooling power needed to melt one short ton of ice in 24 hours and is used to rate air conditioning systems.
What is the difference between watts and volt-amperes?
Watts measure real power (actual work done), while volt-amperes (VA) measure apparent power. In DC circuits they are equal. In AC circuits, watts = VA × power factor, where power factor is typically 0.8-0.95.
Complete list of Power conversion units and its conversion.
- 1 watt [W] = 0.001341022 horsepower (hp)
watts to hp → - 1 watt [W] = 1 joule/second [J/s]
watts to J/s → - 1 watt [W] = 0.000001 megawatt [MW]
watts to MW →
- 1 kilowatt [kW] = 1000 joule/second [J/s]
kW to J/s → - 1 horsepower (hp) = 745.69987158 watt [W]
hp to watts → - 1 horsepower (hp) = 0.7456998716 kilowatt [kW]
hp to kW →
- 1 megawatt [MW] = 1341.0221 horsepower (hp)
MW to hp → - 1 gigawatt [GW] = 1000 megawatt [MW]
GW to MW → - 1 gigawatt [GW] = 1000000 kilowatt [kW]
GW to kW →
- 1 joule/minute [J/min] = 0.016666667 watt [W]
J/min to watts → - 1 kilocalorie (IT)/minute = 69.78 watt [W]
kcal/min to watts → - 1 terawatt [TW] = 1000 gigawatt [GW]
TW to GW →
- 1 horsepower (electric) = 746 watt [W]
electric hp to watts → - 1 horsepower (water) = 746.043 watt [W]
water hp to watts →
- 1 kilowatt [kW] = 1000 watt [W]
kW to watts → - 1 kilowatt [kW] = 1.3410221 horsepower (hp)
kW to hp → - 1 kilowatt [kW] = 0.001 megawatt [MW]
kW to MW →
- 1 horsepower (metric) = 735.49875 watt [W]
hp (metric) to watts → - 1 megawatt [MW] = 1000 kilowatt [kW]
MW to kW → - 1 megawatt [MW] = 1000000 watt [W]
MW to watts →
- 1 ton (refrigeration) = 3516.8528421 watt [W]
ton to watts → - 1 ton (refrigeration) = 3.5168528 kilowatt [kW]
ton to kW → - 1 joule/second [J/s] = 1 watt [W]
J/s to watts →
- 1 volt ampere [VA] = 1 watt [W]
VA to watts → - 1 kilovolt ampere [kVA] = 1000 watt [W]
kVA to watts → - 1 horsepower (boiler) = 9809.5 watt [W]
boiler hp to watts →