Power Unit Converter | Watts & HP
Convert between watts, kilowatts, horsepower, BTU/h, and other power units.
What Is the Power Unit Converter | Watts & HP?
Power is the rate at which energy is transferred or converted, measured in watts (W) in the SI system. One watt equals one joule per second. Different engineering disciplines have developed their own preferred units over centuries, making conversion between them an everyday necessity.
- ›Electrical power, measured in watts, kilowatts, and megawatts. The watt is named after James Watt and is the universal base unit for power in the SI system.
- ›Mechanical power, horsepower (hp) remains dominant in automotive, industrial motors, and aviation. Three variants exist: mechanical (745.7 W), electrical (746 W), and metric/PS (735.5 W).
- ›Thermal power, BTU/hour and tons of refrigeration are used in HVAC, heating systems, and air conditioning capacity ratings across North America.
- ›Energy vs. power, power (watts) measures rate of use; energy (watt-hours, joules) measures total consumption over time. kW × hours = kWh billed by utilities.
Formula
SI Base Unit: Watt (W)
1 W = 1 J/s = 1 kg·m²/s³
Key Conversion Factors (NIST SP 811)
1 kW = 1,000 W
1 MW = 1,000,000 W
1 hp (mechanical) = 745.69987 W
1 hp (electrical) = 746 W
1 hp (metric/PS) = 735.49875 W
1 BTU/hr = 0.29307107 W
1 ton of refrigeration = 3,516.8528 W
1 cal/s = 4.1868 W
| Unit | Symbol | Watts (W) | Category |
|---|---|---|---|
| Milliwatt | mW | 0.001 | Electrical |
| Watt | W | 1 | Electrical |
| Kilowatt | kW | 1,000 | Electrical |
| Megawatt | MW | 1,000,000 | Electrical |
| HP (mechanical) | hp | 745.7 | Mechanical |
| HP (metric/PS) | PS | 735.5 | Mechanical |
| BTU/hour | BTU/hr | 0.2931 | Thermal |
| Ton of refrigeration | RT | 3,516.85 | Thermal |
How to Use
- 1Enter a numeric value in the "Value" field.
- 2Select your source unit from the "From unit" dropdown (e.g., kilowatts, horsepower, BTU/hr).
- 3All equivalent values in every other unit appear instantly, grouped by category.
- 4Click any result row to make that unit the new source, enter a new value to convert from it.
- 5Use the copy button on any row to copy that value to your clipboard.
- 6Click Clear to reset the converter and remove saved state.
Example Calculation
A 100 hp mechanical engine needs to be compared against a European motor rated in kW:
100 hp (mechanical) × 745.69987 W/hp = 74,569.99 W
= 74.57 kW = 0.07457 MW
= 254,423 BTU/hr ≈ 21.2 tons of refrigeration
Common Quick References
- ›1 kW electric heater ≈ 3,412 BTU/hr
- ›1 ton A/C = 12,000 BTU/hr = 3.517 kW
- ›1 horsepower ≈ 0.7457 kW
- ›60 W incandescent bulb ≈ 0.060 kW
- ›100 MW power plant ≈ 134,102 hp
Understanding Power Unit Converter | Watts & HP
How Power Unit Conversion Works
Every power unit converts to and from watts via a fixed multiplication factor. To convert from unit A to unit B, the converter multiplies your input by A's factor to get watts, then divides by B's factor. This single-pivot approach ensures all 14 units stay consistent with no accumulated rounding.
Cross-Discipline Power Comparisons
- ›A standard household circuit (15 A at 120 V) delivers up to 1,800 W = 1.8 kW = 2.4 hp.
- ›A Tesla Model 3 long-range motor outputs ~280 kW = 375 hp peak.
- ›The Hoover Dam generates about 2,074 MW = 2.074 GW = 2,782,000 hp.
- ›The human body at rest dissipates about 80 W; hard exercise peaks at about 400 W.
- ›A typical split A/C unit is 2–5 kW cooling capacity = 6,824–17,060 BTU/hr = 0.57–1.42 tons.
Frequently Asked Questions
What is the difference between mechanical and electrical horsepower?
There are three distinct definitions of horsepower that differ by a few watts:
- ›Mechanical hp, 745.69987 W. Defined as 33,000 foot-pounds per minute. Used for automotive engines and industrial equipment in North America.
- ›Electrical hp, exactly 746 W. Defined by the IEEE for rating electrical motor output. Almost identical to mechanical hp.
- ›Metric/PS (Pferdestärke), 735.49875 W. Defined as lifting 75 kg one metre per second. Used in European car specs and aviation.
- ›Practical impact, A 200 hp engine differs by only about 200 W between definitions, but for high-precision engineering comparisons, always clarify which horsepower standard is being used.
Why does HVAC use BTU/hour instead of watts?
The BTU/hour persists in US HVAC for historical and practical reasons:
- ›Definition, 1 BTU = heat to raise 1 lb of water by 1°F. This connects directly to water-based heating systems that dominated early HVAC design.
- ›Industry convention, "12,000 BTU/hr" for a 1-ton A/C unit is universally understood across the US HVAC industry. Changing to kilowatts would require re-labeling all equipment.
- ›Quick conversion, 1 kW = 3,412 BTU/hr. A 3 kW space heater is therefore ≈ 10,236 BTU/hr, which many manufacturers actually round to 10,000 for simplicity.
- ›International market, Europe, Australia, and most Asian markets use kilowatts for HVAC, so conversion is critical for cross-market equipment comparisons.
What is a "ton of refrigeration" and why is it used?
A ton of refrigeration has a fascinating historical origin in the ice trade:
- ›Historical origin, Before mechanical cooling, businesses purchased cooling by the ton of ice. One ton of refrigeration = the cooling power of melting 2,000 lb of ice in 24 hours.
- ›Exact value, 1 RT = 12,000 BTU/hr = 3,516.8528 W ≈ 3.517 kW. The BTU definition ties back to the latent heat of fusion of water (144 BTU/lb).
- ›Commercial HVAC, Central air conditioning units are routinely specified in tons: a "3-ton" home AC unit provides 36,000 BTU/hr = 10.55 kW of cooling.
- ›Industrial scale, Large refrigeration plants and data center cooling systems still use hundreds or thousands of tons of refrigeration as the preferred unit.
What is the difference between kW and kWh?
The kW vs kWh distinction is one of the most commonly confused concepts in energy:
- ›kW = power, a rate. Like speed (km/h), it tells you how fast energy is being used at any moment. A 2 kW heater draws 2,000 joules every second.
- ›kWh = energy, a quantity. Like distance (km), it accumulates over time. Running the 2 kW heater for 5 hours = 10 kWh of energy consumed.
- ›Electricity billing, utilities bill in kWh. At $0.15/kWh, a 3 kW dryer running 1 hour costs $0.45.
- ›Solar panel output, a 5 kW panel array produces ≈ 5 kWh/hour of peak sun. Annual output estimates (MWh/year) are total energy, not power capacity.
How do I convert horsepower to watts?
Converting horsepower to watts depends on which horsepower definition you use:
- ›Mechanical hp → W: multiply by 745.69987. Example: 100 hp × 745.7 = 74,570 W = 74.57 kW.
- ›Electrical hp → W: multiply by 746. Used for motor nameplates and electric motors.
- ›Metric hp (PS) → W: multiply by 735.49875. Used for European car engine specifications.
- ›Reverse (W to hp): divide watts by the appropriate factor. A 55,000 W industrial motor = 55,000 ÷ 745.7 = 73.75 hp.
What is foot-pound per second (ft·lbf/s) used for?
The foot-pound per second is the parent unit from which horsepower was defined:
- ›Definition, 1 ft·lbf/s = 1.355818 W. It is the power needed to move 1 pound-force through 1 foot in 1 second.
- ›Historical significance, Watt defined 1 hp = 550 ft·lbf/s based on the estimated sustained work rate of a draft horse. This remains the definition of mechanical horsepower.
- ›Where it appears, Structural engineering (beam loading), ballistics (muzzle energy), and classical mechanics problems in US engineering curricula.
- ›Modern use, Largely replaced by watts in practice, but still useful for checking imperial-unit power calculations involving force and velocity in imperial units.
What units does this converter include?
This converter covers 14 units grouped into three categories:
- ›Electrical (5 units), mW, W, kW, MW, GW. Covers everything from microelectronics to power grid transmission.
- ›Mechanical (4 units), HP mechanical, HP electrical, HP metric (PS), ft·lbf/s. For automotive, industrial motors, and classical mechanics.
- ›Thermal (5 units), BTU/hr, BTU/min, cal/s, kcal/hr, ton of refrigeration. For HVAC, heating systems, and food/chemical engineering.
- ›Accuracy, All factors from NIST SP 811 (Guide for the Use of the International System of Units). Calculations run live in your browser with no rounding until display.
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