Power Converter
Convert any power value across 16 units: SI multiples (mW through GW), all four horsepower variants (mechanical, metric, electrical and boiler), BTU/hr, tons of refrigeration, kcal/hr and more. Enter a number, pick its unit, and every equivalent updates instantly alongside plain-English context.
Formula
Worked example
Convert 5 hp to all units: 5 x 745.7 = 3,728.5 W = 3.7285 kW = 0.003729 MW. In HVAC: 3,728.5 / 0.2931 = 12,723 BTU/hr = 1.060 tons of refrigeration. Metric HP: 3,728.5 / 735.5 = 5.069 PS. At $0.16/kWh for 8 hr/day: $0.5965/hr, $4.772/day, $143.16/30 days.
How power unit conversion works
Power is the rate at which energy is transferred or work is done, measured in watts (joules per second) by the SI system. Every other unit has a fixed ratio to the watt, so to convert from any unit to any other, multiply by that unit's factor to reach watts, then divide by the target unit's factor. Because the relationship is a constant ratio, conversions are exact and reversible. This calculator covers 16 units across four families: SI multiples (mW through GW), all four horsepower variants, thermal and HVAC units (BTU/hr, BTU/min, kcal/hr, tons of refrigeration), and mechanical/scientific units (ergs per second, foot-pounds per second).
The four horsepower variants
Horsepower exists in four distinct definitions that differ by a small but measurable amount. Mechanical (imperial) horsepower at 745.7 W is what engine and motor specs quote in the US and UK. Metric horsepower (PS, from the German "Pferdestärke") is 735.5 W, used across continental Europe and Japan for vehicle ratings. Electrical horsepower is exactly 746 W, defined by the US legal code for motor nameplates. Boiler (steam) horsepower is 9,812.5 W, a legacy rating for steam boilers derived from the rate of evaporating water at 212 F. When comparing equipment from different regions or eras, confirming which definition is in use avoids errors of up to about 33 percent between mechanical and boiler HP.
Tons of refrigeration and HVAC power
A ton of refrigeration (TR) is a non-SI unit still widely used in the HVAC industry in North America. It equals 12,000 BTU/hr, which comes from the latent heat required to melt one short ton of ice in 24 hours, about 3,516.85 W. Air conditioner capacity is commonly quoted in both BTU/hr and tons, so a 24,000 BTU/hr unit is a "2-ton" system and draws roughly 7,034 W at rated capacity. This calculator lets you verify those claims and compare to the compressor's electrical draw in kW.
Electricity cost from a power rating
The electricity cost feature converts any power value to an operating cost. The formula is simple: kilowatts multiplied by the rate in dollars per kWh gives the cost per hour. Multiply by daily hours of use to get daily cost, then by 30 for a monthly estimate. The US residential average was about $0.16/kWh in 2024 according to the EIA, but rates vary from under $0.10 in some states to over $0.30 in Hawaii and parts of New England. Enter your own tariff from your electricity bill for a precise figure. Note that this is the cost at continuous rated power; most appliances cycle on and off, so actual bills are lower.
Power conversion reference table
| Watts (W) | kW | Mech. HP | BTU/hr | Tons (TR) | Metric HP (PS) |
|---|---|---|---|---|---|
| 1 | 0.001 | 0.00134 | 3.412 | 0.000284 | 0.00136 |
| 100 | 0.1 | 0.134 | 341.2 | 0.0284 | 0.136 |
| 735.5 | 0.7355 | 0.9863 | 2,509 | 0.209 | 1.000 |
| 745.7 | 0.7457 | 1.000 | 2,545 | 0.212 | 1.014 |
| 1,000 | 1 | 1.341 | 3,412 | 0.284 | 1.360 |
| 3,516.85 | 3.517 | 4.716 | 12,000 | 1.000 | 4.781 |
| 5,000 | 5 | 6.705 | 17,061 | 1.422 | 6.798 |
| 10,000 | 10 | 13.41 | 34,121 | 2.843 | 13.60 |
| 100,000 | 100 | 134.1 | 341,214 | 28.43 | 135.96 |
| 1,000,000 | 1,000 | 1,341 | 3,412,141 | 284.3 | 1,359.6 |
Equivalents rounded for quick lookup. Mechanical HP used throughout. 1 ton of refrigeration = 12,000 BTU/hr = 3,516.85 W.
Frequently asked questions
How many watts are in one horsepower?
It depends on the type: mechanical (imperial) horsepower = 745.69987 W, metric horsepower (PS) = 735.49875 W, electrical horsepower = 746 W (exact), and boiler horsepower = 9,812.5 W. For engine and motor specs the mechanical value of 745.7 W is the standard. This calculator converts all four variants.
How do I convert watts to BTU per hour?
Multiply watts by 3.41214 to get BTU/hr (equivalently, divide BTU/hr by 3.41214 to get watts). The factor comes from 1 BTU = 1,055.056 joules and 1 hour = 3,600 seconds: 1,055.056 / 3,600 = 0.29307 W per BTU/hr, so 1 W = 1 / 0.29307 = 3.412 BTU/hr. A 1,500 W electric heater therefore outputs about 5,118 BTU/hr.
What is a ton of refrigeration and how many watts is it?
A ton of refrigeration is the rate of heat removal needed to freeze one short ton (2,000 lb) of water from 32 F to 32 F ice in 24 hours. That equals 12,000 BTU/hr or approximately 3,516.85 W. A window AC rated at 1 ton cools at 12,000 BTU/hr, drawing roughly 1,000-1,400 W of electricity depending on its efficiency (EER or SEER rating).
What is the difference between metric HP and mechanical HP?
Mechanical (imperial) HP is 745.7 W; metric HP (PS) is 735.5 W, about 1.38% less. European and Japanese car manufacturers historically used PS, so a German car labeled "100 PS" is about 98.6 mechanical HP. Modern specs increasingly quote kW alongside both to avoid the ambiguity.
How do I calculate electricity cost from a wattage?
Divide watts by 1,000 to get kilowatts (kW), then multiply by your rate in dollars per kWh. That gives cost per hour. Multiply by hours of daily use for the daily cost. For example, a 2,000 W appliance at $0.16/kWh costs 2 x 0.16 = $0.32 per hour, $2.56 for 8 hours, and about $76.80 for a 30-day month at that usage.
What is the difference between a watt and a watt-hour?
A watt is a rate of power (energy per second). A watt-hour is a quantity of energy: one watt sustained for one hour = 3,600 joules. To find energy consumed, multiply power in watts by hours. This converter converts power units, not energy units. Use an energy converter for joules, kWh, and BTU conversions.