Watt Converter

About the Watt Converter

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 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 brings the key power units together.

When This Page Helps

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 calculator converts between all 16 units and shows a logarithmic visual comparison so you can intuitively grasp the magnitude. It is most useful when you need to compare mechanical, electrical, HVAC, or RF power on the same scale.

How to Use the Inputs

1. Enter the numeric value you want to convert.
2. Select the source unit from the "From" dropdown.
3. Select the target unit from the "To" dropdown.
4. Read the converted value and all other unit equivalents below.
5. Use presets for common conversions (LED bulb, motor, wind turbine).
6. Check the power comparison visual for a sense of scale.

Example Calculation

Tips & Best Practices

• When converting horsepower, always clarify which HP: mechanical (745.7 W), metric/PS (735.5 W), or boiler (9,810 W). They differ significantly.
• dBm to watts: 0 dBm = 1 mW, 10 dBm = 10 mW, 20 dBm = 100 mW, 30 dBm = 1 W. Each 3 dB doubles the power.
• BTU/h is used for air conditioners, furnaces, and water heaters. 1 ton of cooling = 12,000 BTU/h = 3,517 W.
• Metric horsepower (PS, CV, pk) is used in European and Asian car specifications. It is 1.4% less than mechanical HP.
• For RF link budgets, convert everything to dBm and dB — addition replaces multiplication for gains and losses.
• Power ratings on appliance labels are typically the maximum; actual consumption varies with operating conditions.

History of Power Units

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.

Logarithmic Power Units in RF Engineering

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.

Thermal Power and HVAC

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.

Frequently Asked Questions

• Why are there different types of horsepower?

  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.

• How do I convert dBm to watts?

  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)).

• What is the difference between dBm and dBW?

  dBm references 1 milliwatt; dBW references 1 watt. They differ by 30: dBW = dBm − 30. So 0 dBW = 30 dBm = 1 W.

• How are BTU and watts related?

  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.

• Can I convert power to energy?

  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.

• What is a gigawatt in real terms?

  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.