Home / dBm to mW Converter

By Ali Zafar · Last updated November 2026

dBm to mW Converter

Type a power level and choose its unit. The result shows the same level in dBm, dBW, mW and W, with reference points to give you a feeling for the numbers. Every +3 dB is about twice the power and every +10 dB is ten times the power.

Power level

What it is: the power level you want to convert. It can be negative when the unit is dBm or dBW. How to choose: type the number from the datasheet or the radio settings; a power in mW or W must be more than zero. Example: 20.
What it is: the unit of the value: dBm (decibels against 1 mW), dBW (against 1 W), mW or W. How to choose: radio and Wi-Fi datasheets usually give dBm. Example: dBm.

Converted

—
same power level in every unit
dBm—
mW—
W—
dBW—

Reference points

Only the power level is converted. It does not know about antenna gain, cable loss or the limits of your country. The accepted range is −200 to +100 dBm.

The formulas

ConversionFormula
mW to dBmdBm = 10 × log10(mW)
dBm to mWmW = 10(dBm / 10)
mW to WW = mW / 1000
dBm to dBWdBW = dBm − 30

Quick rules

Every +3 dB doubles the power and every −3 dB halves it (3 dB is a factor of 1.995). Every +10 dB multiplies it by ten. Losses and gains in dB simply add up, which is why radio links are planned in dB.

Worked examples

  • 20 dBm = 100 mW = 0.1 W = −10 dBW.
  • 0 dBm = 1 mW.
  • 1 W = 1000 mW = 30 dBm.
  • 3 dBm = 1.995 mW.
  • 100 mW = 20 dBm.

Common mistakes

  • Adding two dBm values. dBm is an absolute level, so subtract them to get dB, or add dB to a dBm level; do not add dBm to dBm.
  • Mixing up dBm and dBW: dBW is 30 less than dBm for the same power.
  • Forgetting the antenna. The transmit power on the datasheet is not the radiated power; see the EIRP Power Budget calculator.

Frequently asked questions

What is dBm?

dBm is a power level in decibels compared with one milliwatt. 0 dBm is 1 mW, and every 10 dB up is ten times more power.

How do I convert dBm to mW?

Divide the dBm value by 10 and raise 10 to that power. For 20 dBm, 10 to the power 2 is 100 mW.

How many dBm is 1 watt?

1 watt is 1000 mW, which is 30 dBm.

What is the difference between dBm and dBW?

dBm is compared with 1 milliwatt and dBW with 1 watt. The same power is 30 lower in dBW than in dBm.

Why does the calculator reject some values?

The range is limited to −200 to +100 dBm, and a power in mW or W must be above zero because a logarithm of zero or a negative number does not exist.

Related tools

Use the EIRP Power Budget Calculator to turn a transmit level into radiated power. For other conversions in cable work see the Voltage Drop Calculator.

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