Convert between 16 power units: watts, kilowatts, megawatts, horsepower (mechanical, metric, boiler), BTU/hr, dBm, dBW, calories/sec, and more. Log-scale power comparison visual.
Power is expressed in many units depending on the field. Electrical engineers use watts and kilowatts. Mechanical engineers prefer horsepower. HVAC technicians work in BTU/hour. RF engineers think in dBm. This converter bridges all these domains, handling 16 power units including three different horsepower definitions (mechanical, metric, and boiler).
The watt is the SI base: 1 W = 1 J/s. All other units convert through it. Mechanical horsepower (745.7 W) comes from James Watt's 18th-century measurement of draft horses. Metric horsepower (735.5 W, also called PS) is 75 kgf·m/s. Boiler horsepower (9,810 W) is an entirely different unit used for steam boilers. BTU/hour comes from the British thermal unit, linking power to heat.
Enter any value in any unit and instantly see the result in all 16 units. A logarithmic power scale compares your value against everyday references from smartphone chargers to nuclear reactors. Whether you need watts to HP for a motor nameplate, dBm to mW for a WiFi planning link budget, or BTU/hr to kW for an HVAC system, this converter has you covered.
Converting between power units requires memorizing or looking up many conversion factors. The three definitions of horsepower alone (mechanical, metric, boiler) cause frequent confusion. This tool converts instantly between all 16 units and shows a logarithmic visual comparison so you can intuitively grasp the magnitude. Keep these notes focused on your operational context.
Power in watts = Value × Conversion Factor Key factors: 1 HP (mech) = 745.7 W 1 HP (metric) = 735.499 W 1 HP (boiler) = 9,809.5 W 1 BTU/h = 0.29307 W 1 cal/s = 4.184 W dBm: P(W) = 10^(dBm/10) / 1000 dBW: P(W) = 10^(dBW/10)
Result: 149.14 kW
200 mechanical HP × 745.7 W/HP = 149,140 W = 149.14 kW. This is the power output of a typical small car engine. In metric HP (PS): 200 × 745.7 / 735.5 ≈ 202.8 PS.
The watt was named after James Watt in 1882, but Watt himself coined "horsepower" a century earlier to market his steam engines against horses. He measured a mill horse pulling 33,000 foot-pounds per minute and rounded up, giving us 1 HP = 745.7 W. The metric system later defined its own PS (Pferdestärke) unit as a rounder 75 kgf·m/s = 735.5 W.
Radio engineers use dBm (decibels relative to 1 milliwatt) because RF cascades involve many stages of gain and loss. In dBm, a chain calculation becomes addition: transmitter output (30 dBm) − cable loss (3 dB) + antenna gain (6 dBi) − path loss (100 dB) = received power (−67 dBm). This is far simpler than multiplying 1 W × 0.5 × 4 × 10⁻¹⁰.
HVAC systems rate heating and cooling in BTU/hour. One "ton" of cooling (12,000 BTU/h) was historically the heat absorbed by melting one ton of ice per day. Modern heat pumps are rated in both BTU/h and kW. The Coefficient of Performance (COP) compares heat moved to electricity consumed: a COP of 3 means 1 kW of electricity moves 3 kW of heat.
They evolved in different contexts. Mechanical HP (745.7 W) was defined by James Watt. Metric HP (735.5 W) was later defined as exactly 75 kgf·m/s in the metric system. Boiler HP (9,810 W) was defined for steam boiler capacity. They all measure power but with different conversion factors.
Use the formula P(W) = 10^(dBm/10) / 1000. For example: 20 dBm = 10^(20/10) / 1000 = 100/1000 = 0.1 W. Conversely, P(dBm) = 10 × log₁₀(P(mW)).
dBm references 1 milliwatt; dBW references 1 watt. They differ by 30: dBW = dBm − 30. So 0 dBW = 30 dBm = 1 W.
Both measure energy transfer rate. 1 BTU/hour = 0.29307 watts. A 10,000 BTU/h air conditioner equals about 2,930 W or 2.93 kW of cooling capacity.
Multiply power by time: Energy = Power × Time. 1 kW × 1 hour = 1 kWh = 3,600,000 J. Use our Watt-Hours calculator for energy calculations.
A gigawatt (GW) = 1 billion watts. A typical nuclear reactor produces about 1 GW. The entire US power grid capacity is roughly 1,200 GW. "1.21 gigawatts" from Back to the Future is about the output of one nuclear reactor.