dBm to Watts Converter
dBm expresses power on a logarithmic scale relative to one milliwatt, the standard unit for radio, microwave, and optical power levels. It makes it easy to add gains and subtract losses along a signal chain and to read very large and very small powers on one scale. Enter a level in dBm to convert it to watts and milliwatts, or enter a power in watts to convert it back to dBm. This converter handles both directions so you can move freely between linear power and the logarithmic scale.
dBm conversion formula
Power (mW) = 10^(dBm / 10)
Power (W) = Power (mW) / 1,000
dBm = 10 * log10(power in mW)
dBW = dBm - 30
dBm is referenced to one milliwatt, so 0 dBm equals 1 milliwatt. dBW is referenced to one watt, which is 30 dBm less than the same power in dBm.
RF power context
- 0 dBm equals 1 milliwatt; 30 dBm equals 1 watt; 60 dBm equals 1,000 watts.
- Every 10 dBm step multiplies the power by ten; every 3 dBm step roughly doubles it.
- dBm is a power measure and does not depend on impedance until you convert to voltage.
- Gains and losses along a chain add and subtract directly in dBm.
- Negative dBm values represent powers below one milliwatt, common for received radio signals.
dBm to watts: frequently asked questions
What is dBm?
dBm is a power level expressed in decibels relative to one milliwatt. A level of 0 dBm equals exactly 1 milliwatt. It is widely used in radio, microwave, and fibre-optic engineering because it makes large dynamic ranges easy to read and lets gains and losses be added.
How do I convert dBm to watts?
Power in milliwatts equals 10 raised to the power of dBm divided by 10. Divide by 1,000 to get watts. So 30 dBm is 10^3 milliwatts, which is 1,000 milliwatts or 1 watt.
How do I convert watts to dBm?
First convert watts to milliwatts by multiplying by 1,000, then take 10 times the base-10 logarithm: dBm = 10 x log10(power in milliwatts). One watt is 30 dBm and one milliwatt is 0 dBm.
What are some common dBm reference points?
0 dBm is 1 milliwatt, 10 dBm is 10 milliwatts, 20 dBm is 100 milliwatts, 30 dBm is 1 watt, and 60 dBm is 1,000 watts. Negative values are below a milliwatt: -30 dBm is 1 microwatt.
Does dBm depend on impedance?
dBm is purely a measure of power, so it does not depend on impedance by itself. Impedance only matters when you convert between power and voltage, because the relationship between them depends on the load resistance.
Official sources
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.