Conversion tool

Power Converter

Convert between watts, kilowatts, mechanical & electrical horsepower, BTU/hr and tons of refrigeration. All factors referenced to NIST SP811.

From

Formula & conversion factors

1 kW      = 1,000 W  (exact, SI prefix)
1 HP (mech) = 745.6999 W  (550 ft·lbf/s, NIST SP811)
1 HP (elec) = 746 W  (exact, by definition)
1 BTU/hr   = 0.29307 W  (International Table BTU, NIST SP811)
1 Ton (refrig) = 12,000 BTU/hr = 3,516.85 W

General form: value_W = value_unit × factor_to_W
         result = value_W ÷ factor_of_target_unit

1Worked example: a 5 HP motor. 5 × 745.6999 = 3,728.5 W → ÷ 1,000 = 3.7285 kW (typical for a small industrial pump or compressor motor).

Reference standard: Base unit: watt (W), the SI derived unit of power (1 W = 1 J/s = 1 kg·m²/s³). Conversion factors per NIST Special Publication 811. Note: mechanical and electrical horsepower differ slightly (745.70 vs 746 W) — this converter distinguishes both.

Common questions

What is the difference between mechanical and electrical horsepower?

Mechanical HP (also called imperial HP) is defined as 550 ft·lbf/s = 745.70 W. Electrical HP is defined as exactly 746 W. The difference is small (~0.04%) but matters in precise motor specifications.

What is a ton of refrigeration?

One ton of refrigeration equals 12,000 BTU/hr (3,516.85 W). It represents the cooling capacity needed to melt one short ton (2,000 lbs) of ice in 24 hours. It is commonly used to rate air conditioning and chiller capacity.

How do kW and HP relate to motor sizing?

Motor nameplates typically show rated output power. In the US, motors are rated in HP; internationally, in kW. A "1 HP" motor delivers 0.746 kW of mechanical output at rated load. This converter uses the same math as our upcoming 3-phase power calculator.