dBm to watts

dBm is the unit RF engineers actually use — the decibel value of power relative to one milliwatt. The anchor is easy: 30 dBm is exactly 1 W, 20 dBm is 100 mW, and 0 dBm is 1 mW. A Wi-Fi access point transmits around 20–23 dBm; a phone about 23–27 dBm; a licensed radio up to 40 dBm (10 W). This calculator converts the dBm on your equipment label into the watts that feed your transmitter math.

W = 10^((dBm − 30) ÷ 10). dBm is a logarithmic power ratio referenced to one milliwatt: 0 dBm = 1 mW, 20 dBm = 0.1 W and 30 dBm = 1 W. Every 10 dB is a factor of ten; every 3 dB is roughly a doubling.

By EnginStack Editorial Team | Reviewed against NIST, BIPM and primary-source documentation About →
dBm
— watts
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Constants verified against NIST Special Publication 811 (Guide for the Use of the International System of Units) and the 1959 International Yard and Pound Agreement. All values are exact — none are rounded approximations.

dBm to watts

The dBm scale is logarithmic because power in RF spans orders of magnitude — from microwatts to kilowatts — and decibels compress that range into readable numbers. The conversion is exact: P(W) = 10^((dBm−30)/10), since dBm is dB relative to 1 mW and 0 dBm = 1 mW = 0.001 W. Regulatory limits, antenna gain calculations, and link budgets all work in dBm, but equipment power and heat dissipation work in watts — so the conversion is a daily tool for anyone who touches radio equipment.

watts = 10^((dBm − 30) / 10)
30 dBm = 1 W  ·  20 dBm = 0.1 W  ·  0 dBm = 1 mW
The conversion is exact — dBm is dB relative to 1 milliwatt.

Worked Examples

Example 1: Convert a 30 dBm transmitter

10^((30 − 30)/10) = 1 W

Example 2: Convert a 20 dBm access point

10^((20 − 30)/10) = 10⁻¹ = 0.1 W

Example 3: Convert a 40 dBm amateur transmitter

10^((40 − 30)/10) = 10¹ = 10 W

Common dBm to watts Values

dBmwattsContext
0 dBm—0.001 W1 mW — the dBm anchor.
20 dBm—0.1 WIndoor Wi-Fi access point.
23 dBm—0.2 WConsumer Wi-Fi at max.
30 dBm—1 WThe 30 dBm = 1 W milestone.
40 dBm—10 WLicensed two-way radio.

Engineering Context

dBm-to-watts is the power-side companion to watts to dBm, and both live at the junction of the electric hub and the energy family — the watt is the shared unit. Link budgets that add and subtract dBm connect to the frequency world via the frequency hub (Wi-Fi at 2.4/5 GHz).

The anchor to memorize is thirty decibel milliwatts equals one watt, and almost every other value on this page can be reached from it by adding or subtracting three decibels for a doubling or halving of power. Radio equipment, spectrum regulators and safety assessments all work in this pair, because radiated power spans an enormous range and a linear scale would need ten digits to hold it. The same arithmetic runs a link budget: transmitted power in decibel milliwatts, minus path loss, plus antenna gains, must exceed the receiver sensitivity in decibel milliwatts, and the margin is the difference between a usable link and an intermittent one.

More: W to dBm · dBm to mW · W to kW · Electric Guide · Electric Hub

Related Unit Converters

watts to dBm dBm to milliwatts Watts to Kilowatts Electric Conversion Guide Electric Converters

Frequently Asked Questions

How many watts is 30 dBm?

Exactly 1 watt. The dBm scale is relative to 1 mW, so 30 dBm = 10^(30/10) mW = 1,000 mW = 1 W. It is the best-known anchor in RF power.

What does dBm mean?

Decibels relative to one milliwatt: 0 dBm = 1 mW, and every 10 dB multiplies power by 10. It is a logarithmic scale that compresses the huge power range of radio signals into readable numbers.

Why is Wi-Fi limited to about 20–23 dBm?

Regulators cap consumer Wi-Fi transmit power (typically 1 W EIRP in the US, which is 30 dBm including antenna gain). Access points run at 20–23 dBm of actual transmitter power to stay under the limit with antenna gain included.