Power Converter

What this converter does

Power is the rate energy flows, from the few watts a light bulb draws to the gigawatts a power station delivers. This converter spans that whole range, adds horsepower for engines, and includes the decibel units (dBm and dBW) used for radio and signal power.

How to use it

• Type your power value into the value box.
• Set From to the unit you have, and To to the unit you want.
• Press Calculate.

The result reads back in plain words, like "1 hp is equal to 745.7 W." Use Swap to flip the two units, and Reset to clear.

How it works

Most units here are tied to the watt by a simple factor: a kilowatt is 1,000 watts, a megawatt is a million, a horsepower about 746. Your value is converted to watts and then to the target unit. The decibel units are the exception, and they get their own section just below, because they are logarithmic rather than a plain multiply.

The decibel units: dBm and dBW

A decibel scale is logarithmic, which means it measures ratios rather than fixed amounts. dBm measures power against a reference of one milliwatt, and dBW against one watt:

• dBm = 10 × log10(power in milliwatts)
• dBW = 10 × log10(power in watts)

The payoff is that enormous and tiny powers fit on one small, readable scale. Every 10 dB is a tenfold change in power, and every 3 dB is roughly a doubling. So 0 dBm is 1 milliwatt, 10 dBm is 10 milliwatts, 20 dBm is 100 milliwatts, and 30 dBm is a full watt. Because a watt is 1,000 milliwatts, a dBW figure is always 30 lower than the same power in dBm: 1 watt is 0 dBW and 30 dBm at the same time. You will meet these units in radio, WiFi, and fibre-optic work, where signal powers span a huge range. A home WiFi router, for example, transmits at around 20 dBm, which is 100 milliwatts.

One catch worth knowing: a dBm or dBW value can be negative, since a negative dBm simply means less than a milliwatt. But the power you start from has to be positive, because a logarithm is undefined for zero or a negative value.

Common power conversions

A few worth keeping handy:

Power or energy: which one you need

Power and energy are easy to confuse, so here is the line between them. Power is a rate, how fast energy is being used or delivered, measured in watts. Energy is the total amount that adds up over time.

A 2,000-watt kettle has a power of 2 kilowatts, but the energy it uses depends on how long it runs. So if you are converting joules, calories, or kilowatt-hours, those are amounts of energy, and the Energy Converter is the tool you want. Watts, kilowatts, horsepower, and the decibel units all belong here.

Questions people ask

References

1. National Institute of Standards and Technology (NIST), Office of Weights and Measures. The International System of Units (SI) and the watt. https://www.nist.gov/pml/owm/metric-si/si-units