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Power Unit Quick Reference
- Watt (W): SI base unit — 1 joule per second
- Kilowatt (kW): 1,000 W — household appliances, EV charging
- Megawatt (MW): 1,000,000 W — power plants, large facilities
- Gigawatt (GW): 1,000,000,000 W — national grid scale
- Mechanical Horsepower (hp): 745.7 W — US automotive standard
- Metric Horsepower (PS/CV): 735.5 W — European automotive standard
- BTU/hour: 0.293 W — HVAC and heating equipment
- Calorie/second: 4.184 W — thermodynamics and nutrition
Examples
Example 1: Watts to Horsepower (Engine Power)
Convert: 150,000 W (150 kW) to horsepower
Mechanical Horsepower (hp): 150,000 ÷ 745.7 = 201.1 hp
Metric Horsepower (PS/CV): 150,000 ÷ 735.5 = 203.9 PS
Note: A 150 kW electric vehicle motor produces
approximately 201 mechanical horsepower.
Metric horsepower (used in Europe) differs by ~1.4%.
Example 2: Horsepower to Watts (Comparing Engines)
Convert: 450 hp (mechanical) to watts and kilowatts
450 hp × 745.7 = 335,565 W = 335.6 kW
Convert: 450 PS (metric horsepower) to watts
450 PS × 735.5 = 330,975 W = 331.0 kW
Difference between 450 hp and 450 PS: 4,590 W (4.6 kW)
Always clarify which horsepower standard is being used
when comparing international engine specifications.
Example 3: BTU/hour to Watts (HVAC and Cooling)
Convert: 12,000 BTU/hr (1-ton air conditioner) to watts
12,000 BTU/hr ÷ 3.412 = 3,517 W = 3.517 kW
Common HVAC conversions:
6,000 BTU/hr = 1,758 W (small window unit)
12,000 BTU/hr = 3,517 W (1 ton — standard room AC)
18,000 BTU/hr = 5,275 W (1.5 ton)
24,000 BTU/hr = 7,034 W (2 ton)
36,000 BTU/hr = 10,551 W (3 ton — central AC)
60,000 BTU/hr = 17,584 W (5 ton — large system)
BTU/hour is the standard unit for HVAC equipment in the US. Converting to watts is essential when comparing equipment from different manufacturers or calculating electrical load.