Power reference
Technical unit workspace
- Quantities
- 3
- Systems
- SI / US
Common power units:
- Watt (W): SI unit of power
- Kilowatt (kW): 1,000 watts
- Horsepower (hp): 745.7 watts
- BTU/hour: heating/cooling power
- Volt-ampere (VA): apparent power
Key relationships:
- 1 hp = 745.7 W = 0.7457 kW
- 1 kW = 1.341 hp = 3,412.14 BTU/h
- 1 BTU/h = 0.2931 W = 0.0003931 hp
Origins of Power Units:
The watt (W) was introduced in the late 18th century, named after James Watt, the Scottish engineer who significantly improved the steam engine. It was officially adopted as the SI unit of power in 1960.
Horsepower Development:
Horsepower was defined by James Watt in the 1780s to compare steam engine output to draft horses. Several standards developed: mechanical/imperial horsepower (745.7 W), metric horsepower/PS (735.5 W), and electrical horsepower (746 W).
Thermal Units:
The British Thermal Unit (BTU) emerged in the late 19th century from heating applications. BTU per hour became standard for HVAC system ratings and remains widely used, especially in the United States.
Watts are used for:
- Household electronics and lighting
- Small electrical devices
- Solar panel output ratings
- Computer component power consumption
Horsepower is used for:
- Vehicle engines (especially in US/UK)
- Industrial motors and engines
- Pumps and compressors
- Lawn equipment and power tools
Other units:
- BTU/hour: HVAC systems, heaters
- kW and MW: electrical utilities
- VA and kVA: electrical equipment rating
- W/m²: solar radiation, heat flux
Power Conversion Calculator
Quick answer
Formula: kW = hp x 0.7457
Converting Horsepower to Kilowatt with 6-place display precision.
Measurement type
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Quick pairs
Jump to the most common unit combinations
Quantity
Power
Input unit
Horsepower (hp)
Output unit
Kilowatt (kW)
Popular power pair converters
Published horsepower ↔ kilowatt calculators and the related energy pair pages.
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What are Power Measurements?
Power measurements quantify the rate at which energy is transferred, used, or transformed. The fundamental unit of power is the watt (W), defined as one joule of energy per second (J/s). Power is a crucial measurement in electrical, mechanical, thermal, and many other engineering and scientific applications.
Different power units evolved to suit various industries and applications. While watts and kilowatts are standard in electrical applications, horsepower remains common for engines and motors, BTU per hour for heating and cooling systems, and watt per square meter for radiation intensity measurements.
Learn more from NIST or Bureau International des Poids et Mesures (BIPM).
Common Power Conversions
| From | To | Multiply By | Example |
|---|---|---|---|
| Watts (W) | Horsepower (hp) | 0.001341 | 1,000 W = 1.341 hp |
| Horsepower (hp) | Watts (W) | 745.7 | 1 hp = 745.7 W |
| Watts (W) | BTU/hour | 3.412142 | 1,000 W = 3,412.14 BTU/h |
| BTU/hour | Watts (W) | 0.2931 | 1,000 BTU/h = 293.1 W |
| Kilowatts (kW) | Horsepower (hp) | 1.341 | 1 kW = 1.341 hp |
| Metric horsepower (PS) | Watts (W) | 735.5 | 1 PS = 735.5 W |
| Foot-pound/second | Watts (W) | 1.3558 | 1 ft·lbf/s = 1.3558 W |
Power Density Conversions
| From | To | Multiply By | Example |
|---|---|---|---|
| W/m² | BTU/h·ft² | 0.3170 | 1,000 W/m² = 317 BTU/h·ft² |
| BTU/h·ft² | W/m² | 3.1546 | 100 BTU/h·ft² = 315.46 W/m² |
| hp/in³ | kW/L | 45.5 | 1 hp/in³ = 45.5 kW/L |
| W/kg | hp/lb | 0.0006083 | 1,000 W/kg = 0.6083 hp/lb |
Practical Applications of Power Conversions
Electrical Engineering
- Sizing electrical panels, wiring, and circuit breakers based on wattage
- Converting between apparent power (VA) and real power (W) using power factor
- Calculating three-phase power for industrial equipment
- Determining electrical energy consumption (kWh) from power ratings
Mechanical Engineering
- Converting between mechanical horsepower and kilowatts for motors and engines
- Calculating power requirements for pumps, fans, and compressors
- Determining power transmission through gears, belts, and chains
- Evaluating power-to-weight ratios for vehicle performance
HVAC & Building Systems
- Converting between BTU/hour and kilowatts for heating and cooling systems
- Sizing air conditioning units based on room size and heat load
- Calculating heat flux through building materials (W/m²)
- Determining energy efficiency ratios for heating/cooling equipment
Renewable Energy
- Calculating solar panel output based on irradiance (W/m²) and panel area
- Sizing battery storage systems based on power requirements
- Determining wind turbine capacity factors from rated power
- Comparing energy production capacity across different technologies
Consumer Applications
- Understanding power consumption ratings on household appliances
- Comparing automobile engine power specifications across regions
- Calculating electricity costs based on device wattage and usage time
- Selecting appropriate power tools based on horsepower or wattage ratings
Educational Resource
This comprehensive tutorial from The Organic Chemistry Tutor has over 1.5 million views and explains unit conversions with a focus on power units like watts, horsepower, and joules per second. The video provides a detailed walkthrough of dimensional analysis methods essential for engineering, physics, and practical applications involving power measurements.
Power Conversion Resources
Get our comprehensive power conversion chart showing relationships between watts, horsepower, BTU/hour, and other power units for quick reference in your engineering calculations and everyday applications.
Power Conversion FAQs
Find answers to common questions about power measurements and conversions.
What are the main units used for measuring power?
The main power measurement units are: 1) Watt (W) - SI unit of power, 2) Horsepower (hp) - mechanical/electrical power, 3) Kilowatt (kW) - larger power measurements, 4) BTU/hour - heating/cooling power, 5) Megawatt (MW) - industrial scale power, 6) VA (volt-amperes) - apparent power in AC systems.
How do you convert between watts and horsepower?
To convert between watts and horsepower: 1) 1 horsepower = 745.7 watts, 2) 1 kilowatt = 1.341 horsepower, 3) For quick estimates: 750W ≈ 1 hp, 4) For mechanical horsepower: 1 hp = 550 ft⋅lbf/s, 5) For metric horsepower: 1 PS = 735.5 watts, 6) Electric motor ratings often use hp in US/UK.
What is the difference between power and energy?
Power and energy differences include: 1) Power is rate of energy use (watts), 2) Energy is total power over time (watt-hours), 3) Power × Time = Energy (e.g., 1000W × 1 hour = 1kWh), 4) Power is instantaneous, energy is cumulative, 5) Utility bills measure energy (kWh), not power.
How do you calculate electrical power?
Calculate electrical power using: 1) DC power: P = V × I (voltage × current), 2) AC power: P = V × I × PF (power factor), 3) Three-phase power: P = √3 × V × I × PF, 4) Resistive power: P = I²R, 5) Apparent power: VA = V × I, 6) Real power: W = VA × power factor.
What power ratings are common for different applications?
Common power ratings include: 1) Household appliances: 100W-2000W, 2) Electric motors: 0.25-100 hp, 3) Power tools: 500W-2500W, 4) HVAC systems: 1-5 tons (3.5-17.5 kW), 5) Solar panels: 250-400W per panel, 6) Electric vehicles: 50-200 kW, 7) Industrial machinery: 1-1000 hp.
How do you convert between power density units?
Power density conversions include: 1) Watts per square meter (W/m²), 2) BTU per hour per square foot (BTU/h⋅ft²), 3) Horsepower per cubic foot (hp/ft³), 4) Kilowatts per cubic meter (kW/m³), 5) Solar irradiance: 1000 W/m² = 317.1 BTU/h⋅ft², 6) Engine power density: 1 hp/ft³ = 35.315 kW/m³.
What factors affect power measurements?
Power measurements are affected by: 1) Load conditions and variations, 2) Power factor in AC systems, 3) Temperature effects on efficiency, 4) Measurement instrument accuracy, 5) System losses and inefficiencies, 6) Operating environment, 7) Equipment maintenance condition.
How do you choose the right power unit for calculations?
Choose power units based on: 1) Industry standards (HVAC uses BTU/h, motors use hp), 2) Scale of application (household uses watts, utilities use megawatts), 3) Regional conventions (US uses hp, Europe uses kW), 4) Calculation requirements, 5) Equipment specifications, 6) Regulatory requirements.
Power conversion shortcuts
Power calculator links for watts, kilowatts, horsepower and engineering references.