About the Power Converter
Power is how fast energy is used or delivered. This converter changes a power value between watts, kilowatts, megawatts, milliwatts, mechanical horsepower, metric horsepower (PS), BTU per hour, tons of refrigeration, calories per second and ergs per second, and lists the same value in every unit. A separate section switches between dBm and watts for radio and signal work. Horsepower has several definitions: this page uses the mechanical one (745.7 W) and the metric one (735.5 W) only, and does not convert engine ratings measured to different standards such as SAE or DIN. dBm assumes power referenced to 1 milliwatt.
Updated September 2026
How to use the Power Converter
- 1Type a power value in the Value box.
- 2Choose the unit you have in From and the unit you want in To.
- 3Read the answer, or use the table to see every unit at once.
- 4For radio power, type dBm or watts in the dBm section and read the other box.
- 5Press Copy to keep any number.
Power units and what they measure
Power is energy per unit of time. One watt is one joule every second. Everyday appliances are rated in watts or kilowatts, engines in horsepower, heating and cooling in BTU per hour, and weak radio signals in milliwatts or dBm. Because all of these measure a rate, they convert to each other by a simple multiplier, and this page goes through watts as a common base.
Horsepower explained
The word horsepower was invented to compare steam engines with draught horses, and the number has since been fixed in more than one way. Mechanical horsepower is 745.7 watts. Metric horsepower is 735.5 watts and appears on European car specifications as PS or CV. Electric motors are sometimes rated at exactly 746 watts per horsepower, which is close to the mechanical figure but not listed here.
Ratings measured under different test standards can also differ from each other, and no converter can adjust for that.
Air conditioning: BTU/h and tons
These figures are for cooling output. The electricity the unit draws is usually lower, depending on its efficiency.
- 1 kW is about 3,412 BTU/h
- 1 ton of refrigeration is 12,000 BTU/h
- 1 ton is about 3.517 kW of cooling
- A 9,000 BTU/h room unit removes about 2.6 kW of heat
Radio signals: dBm and watts
Decibel-milliwatts express power on a logarithmic scale against 1 milliwatt. Adding 10 dBm multiplies the power by ten, and adding 3 dBm roughly doubles it. Wi-Fi transmitters commonly run near 20 dBm, which is 100 milliwatts. For other units, use the Unit Converter, and use the Calorie Calculator for food energy. The Percentage Calculator and Online Calculator help with any sums along the way.
Features
- Ten power units in one converter
- Mechanical and metric horsepower shown separately
- BTU per hour and tons of refrigeration for heating and cooling
- Two-way dBm and watts
- Table of the value in every unit with Copy buttons
- Scientific notation for very small or large values
- Runs in your browser
Frequently asked questions
How do I convert horsepower to kilowatts?
Multiply mechanical horsepower by 0.7457. So 1 hp is about 0.7457 kW, and 100 hp is about 74.57 kW. Choose hp in From and kW in To to see the exact figure.
What is the difference between hp and PS?
Mechanical horsepower (hp) is 745.7 watts, and metric horsepower (PS, or CV) is 735.5 watts. The two differ by about 1.4 percent, so a car listed as 150 PS is roughly 148 hp.
How many BTU per hour is a kilowatt?
One kilowatt is about 3,412 BTU per hour, using the International Table BTU. That is why a 1.5 kW electric heater gives about 5,100 BTU/h.
How much power is a ton of air conditioning?
A ton of refrigeration is 12,000 BTU per hour, about 3.517 kW of cooling. It is a measure of heat removed, not of the electrical power the unit consumes.
How do I convert dBm to watts?
Use 0.001 watts times ten to the power of dBm divided by ten. 30 dBm is 1 W, 0 dBm is 1 mW, and every 10 dBm multiplies the power by ten. Type the dBm value in the dBm section and read the watts.
Is a kilowatt the same as a kilowatt-hour?
No. A kilowatt is a rate of using energy; a kilowatt-hour is the energy used by running 1 kW for an hour. For energy units, use the Energy Converter.
Why can watts not be zero for dBm?
dBm is a logarithm, and the logarithm of zero or a negative number does not exist. Enter a value above 0 watts to get a dBm figure.