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Power Conversion Calculator

Convert power between watts, kilowatts, horsepower, BTU/hr, and other power units instantly.

Energy Extrapolator

74.57

Converted Power

74.57
Kilowatts (kW)
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What is Power Units: Watts, Horsepower & BTU/hr?

How the Watt (the SI unit of power) relates to the mechanical horsepower, the metric horsepower, and the thermal BTU/hr — and their shared definition as energy delivered per unit time.

Mathematical Foundation

Definition of Power
P=ΔEΔtP = \frac{\Delta E}{\Delta t}
ΔE\Delta E= Energy transferred or work done (in Joules)
Δt\Delta t= Time elapsed (in seconds)
PP= Power in Watts (1 W = 1 J/s)

Laws & Principles

  • The Horsepower's Origin: James Watt coined 'horsepower' in 1782 to market steam engines to coal mine operators who used horses. He defined 1 hp = 33,000 ft·lbf/min — approximately the sustained power output of a draft horse over a long day. Modern engines use this as a marketing unit, but 1 mechanical hp = 745.7 watts exactly.
  • BTU/hr vs Watts for HVAC: Air conditioner and heater capacity is expressed in BTU/hr (British Thermal Units per hour) in the US. 1 BTU/hr represents melting 1 lb of ice over 140 minutes. 1 Watt = 3.412 BTU/hr. A 10,000 BTU/hr window AC unit is therefore roughly a 2,931W (or ~2.9kW) load on the electrical system.

Step-by-Step Example Walkthrough

" Converting 100 horsepower (mechanical) to kilowatts and BTU/hr. "

  1. 1 mechanical hp = 745.7 Watts exactly.
  2. 100 hp × 745.7 = 74,570 Watts = 74.57 kW.
  3. 1 Watt = 3.412 BTU/hr.
  4. 74,570 W × 3.412 = 254,388 BTU/hr.
Final Result: 100 hp = 74.57 kW = 254,388 BTU/hr

Quick Answer: Common Power Conversions

1 horsepower = 745.7 watts. 1 kilowatt = 1.341 HP. 1 BTU/hr = 0.293 watts. In HVAC, a "ton" of cooling = 12,000 BTU/hr = 3,517 watts. Mechanical horsepower (HP), electrical horsepower, and metric horsepower (PS) are all slightly different — this calculator handles all three.

Power Unit Reference

Unit= WattsCommon Use
1 Horsepower (HP)745.7 WEngines, motors
1 Kilowatt (kW)1,000 WEV motors, appliances
1 BTU/hr0.293 WHVAC heating/cooling
1 Ton (HVAC)3,517 WAir conditioning capacity
1 Metric HP (PS)735.5 WEuropean car specs

Frequently Asked Questions

What is the difference between HP and PS?

HP (mechanical horsepower) = 745.7 watts. PS (Pferdestärke, metric horsepower) = 735.5 watts. The difference is about 1.4%. European car manufacturers use PS, US uses HP. A "300 PS" European car is actually 296 HP. When comparing specs between US and European cars, always check which unit is used.

Why are HVAC systems rated in BTU and tons?

A "ton" of cooling originated from the ice trade — it's the power needed to melt one ton (2,000 lbs) of ice in 24 hours, which equals 12,000 BTU/hr or 3,517 watts. Residential AC units are typically 1.5-5 tons. The BTU system persists because the US HVAC industry never fully adopted metric units. A typical home needs about 400 sq ft per ton of cooling capacity.

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