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dBm to Watts Converter

Type a level in dBm to get watts and milliwatts, or a power in watts to get dBm. The formula is shown with the result, so you can check it by hand.

Power

1 W

1000 mW · 10^((30 − 30) ÷ 10)

dBm is a power measured against 1 milliwatt: 0 dBm = 1 mW, 30 dBm = 1 W. Values are rounded to 6 significant digits for display.

How it works

  1. Choose the direction: dBm to watts, or watts to dBm.
  2. Enter the value: a level in dBm (it can be negative) or a power in watts above 0.
  3. Read the result with the formula, in watts and milliwatts or in dBm.
  4. Copy the conversion into your notes or your message.

What people use it for

  • Radio and amateur radio

    Turn a transmitter's output in watts into dBm to add the gain and the losses of a feed line.

  • Wi-Fi and wireless modules

    Read a datasheet in dBm as milliwatts and compare two radios on the same scale.

  • Checking a link budget

    Convert each step of a power calculation back to watts to see the real amounts.

Questions

What is the formula?
Power in watts = 10 raised to ((dBm − 30) ÷ 10). In reverse, dBm = 10 × log10(power in watts) + 30. So 0 dBm is 1 mW (0.001 W), 30 dBm is 1 W and 40 dBm is 10 W.
Why can I not enter 0 watts?
Because 0 W would be minus infinity in dBm, which is not a number. Enter a small positive power instead: 0.000001 W is −30 dBm.
Does 3 dB really double the power?
About: +3 dB multiplies the power by 1.995, and −3 dB halves it almost exactly. Each +10 dB multiplies it by 10.
Is dBm the same as dB?
No. dB is a ratio between two powers; dBm is a power measured against 1 milliwatt. You add and subtract dB values, and a dBm value plus a dB gain stays in dBm.