Power Converter

The power converter translates between watts, kilowatts, megawatts, horsepower, BTU per hour, and other units of power. It is designed for engineers, electricians, and anyone comparing engine ratings, appliance specifications, or energy system outputs.

How to Use the Power Converter

1. Enter the power value you want to convert.
2. Select the unit you are converting from, such as horsepower or kilowatts.
3. Select the unit you are converting to, such as watts or BTU/hour.
4. Read the converted value in the results panel.
5. Perform additional conversions as needed.

The Formula

Power is the rate at which energy is transferred or work is done. The SI unit is the watt (W), defined as one joule per second.

Key conversion factors:

• 1 kilowatt (kW) = 1,000 watts
• 1 megawatt (MW) = 1,000,000 watts
• 1 mechanical horsepower (hp) = 745.7 watts
• 1 metric horsepower (PS) = 735.5 watts
• 1 BTU per hour (BTU/hr) = 0.2931 watts
• 1 foot-pound per second = 1.356 watts

To convert between any two units, divide the source value by the source conversion factor to get watts, then divide by the target conversion factor.

For example, to convert horsepower to kilowatts:

kW = hp x 0.7457

Real-World Example

A car engine is rated at 200 mechanical horsepower. You want to know its power output in kilowatts, as European specifications typically use kW.

• 200 hp x 0.7457 = 149.1 kW

This is why a car marketed as "200 hp" in the US might be listed as "149 kW" in a UK or European brochure. The values describe the same engine.

Now suppose you want to know how many BTUs per hour that engine produces at full power:

• 149,140 watts / 0.2931 = 508,900 BTU/hr

This figure would be relevant for calculating heat output or cooling requirements in an enclosed space.

Power vs Energy: An Important Distinction

Power and energy are related but different. Power is the rate of energy transfer (watts), while energy is the total amount transferred over time (watt-hours or joules). A 100-watt light bulb running for 10 hours uses 1,000 watt-hours (1 kWh) of energy. On your electricity bill, you pay for energy (kWh), not power (kW). Understanding this distinction matters when comparing appliance running costs or sizing a solar installation.

Frequently Asked Questions

What is the difference between mechanical horsepower and metric horsepower? Mechanical horsepower (used in the US and UK) equals 745.7 watts, defined originally as the power of a steam engine relative to a horse. Metric horsepower (PS, used in continental Europe) equals 735.5 watts, defined as the power to lift 75 kg by one metre per second. The difference is about 1.4%, so it matters in precise engineering but is negligible for most comparisons.

Why do electrical appliances use watts while engines use horsepower? This is largely a historical convention. Electrical engineering adopted SI units (watts) early on, while the automotive and mechanical engineering industries in the US and UK retained horsepower as a familiar commercial unit. Both measure the same physical quantity.

How many watts does a typical household use? Average UK household electricity consumption is around 3,100 kWh per year, which equates to an average continuous draw of about 354 watts. Peak demand is much higher when appliances like kettles (around 2,500 W) or electric ovens (around 2,000 W) run simultaneously.

What is a megawatt used to measure? Megawatts (MW) describe the output of power stations, large industrial facilities, and grid-scale renewable energy installations. A typical onshore wind turbine generates 2 to 3 MW. A large gas-fired power station may produce 1,000 MW (1 GW).

Why do car engines still use horsepower?

Buyers in the US and UK have read engine output in horsepower for a century, so the figure is kept for familiarity even though the SI unit is the kilowatt. A 200 hp engine is a 149 kW engine, and both numbers describe the same output. Use the converter above to check any specific figure against the unit you were given.

How many watts is one ton of refrigeration?

3,516.85 W, because a ton of refrigeration is defined as 12,000 BTU per hour and one BTU per hour is 0.2930711 W. Commercial cooling equipment is sold in tons in the US and in kilowatts in Europe, so the two figures appear side by side in specifications. Plug your own number into the converter above.

Does a larger wattage always mean a better appliance?

No. Watts measure the rate of energy use or output, and the useful figure is the energy consumed or delivered per task. A 1,500 W microwave and an 800 W microwave can both heat a meal, with the lower-rated one taking longer. Compare kilowatt-hours per completed task, not the nameplate rating.

A conversion table for power units

Every factor below is stated in watts, and the converter pivots through watts: divide the source value by the source factor, then divide by the target factor. That keeps one table instead of a table for every pair of units.

Worked conversions you can check

A 3.5 kW electric motor is rated for the European market and you need a horsepower figure.

• In mechanical horsepower: 3,500 / 745.6999 = 4.69 hp.
• In metric horsepower: 3,500 / 735.4988 = 4.76 hp.
• In BTU per hour: 3,500 / 0.2930711 = 11,942.5 BTU/h.

The gap between the two horsepower figures is 1.4%, which is the whole difference between the units rather than a rounding error in the source document. Quoting the wrong one on a specification sheet is a real mistake.

A 12,000 BTU/h air conditioner sold as a one-ton unit:

• 12,000 x 0.2930711 = 3,516.85 W, or 3.52 kW.
• 12,000 / 12,000 = 1.00 ton of refrigeration, by definition.

A 1.5 kW kettle draws 1,500 W:

• In horsepower: 1,500 / 745.6999 = 2.01 hp.
• In foot-pounds per second: 1,500 / 1.3558179 = 1,106.34 ft-lbf/s.

At 230 V that kettle draws 6.5 A, while a 3 kW kettle draws 13.0 A, which is the entire rating of a UK 13 amp plug. The amps figure matters more than the watts when you are deciding what can share a circuit.

Horsepower and torque measure different things

Power is a rate of doing work. Torque is a turning moment. The two connect through engine speed: horsepower equals torque in pound-feet multiplied by revolutions per minute, divided by 5,252. That constant is 33,000 foot-pounds per minute divided by 2 pi radians per revolution.

A 200 hp engine at 4,000 rpm develops 5,252 x 200 / 4,000 = 262.6 lb-ft of torque at that speed. The same 200 hp at 2,000 rpm needs 525.2 lb-ft. Peak power and peak torque therefore arrive at different engine speeds, which is why a diesel engine pulls hard low in the rev range and a petrol engine makes its power near the red line. Neither figure converts to the other without the rpm.

Method and rounding

The converter pivots through watts for two reasons. One factor table replaces a matrix of pairwise factors, and adding a new unit costs one row rather than one row per existing unit. Rounding also happens once, at the end of the chain, rather than at each step.

The factors themselves are exact where the unit is defined rather than measured. A ton of refrigeration is 12,000 BTU per hour by definition, and a BTU is 1,055.05585262 joules under the International Table. Metric horsepower is 75 kilogram-force metres per second, which is 735.49875 W once you fix gravity at 9.80665 m/s squared. Printing four significant figures suits engineering comparison. Carry more only when the result feeds another calculation.

SI prefixes on the watt

The watt takes the standard metric prefixes, and grid-scale figures move in steps of a thousand.

Moving from MW to GW means dividing by 1,000, so a 2.5 MW turbine is 0.0025 GW and a 1,000 MW station is 1.0 GW. Mixing the steps is the most common error in a plant capacity table, and it survives review because the numbers still look plausible.

Sources

• NIST Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811. Accessed 2026-09-13.
• US Energy Information Administration, energy conversion calculators. https://www.eia.gov/energyexplained/units-and-calculators/energy-conversion-calculators.php. Accessed 2026-09-13.

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• Energy Converter
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