dBm to Watts Converter
Convert dBm, dBW, watts, milliwatts and kilowatts to each other, with a table of common levels and the formulas, for RF, antenna and signal power.
Common levels
| dBm | Milliwatts | Watts | dBW |
|---|---|---|---|
| -30 | 0.001 | 0.000001 | -60 |
| -10 | 0.1 | 0.0001 | -40 |
| 0 | 1 | 0.001 | -30 |
| 3 | 1.995262 | 0.001995262 | -27 |
| 10 | 10 | 0.01 | -20 |
| 20 | 100 | 0.1 | -10 |
| 30 | 1000 | 1 | 0 |
| 40 | 10000 | 10 | 10 |
| 50 | 100000 | 100 | 20 |
| 60 | 1000000 | 1000 | 30 |
Formulas
dBm = 10 × log10(P in mW)
dBW = 10 × log10(P in W)
P in W = 10^(dBm / 10) ÷ 1000
dBW = dBm − 30
Why a logarithmic scale
Signal and antenna powers span many orders of magnitude, so a logarithmic scale keeps the numbers short, and gains and losses add and subtract. A 20 dB amplifier followed by a 6 dB cable loss is a net 14 dB. The decibel is a ratio, so a level in dBm or dBW always refers to a stated power.
Power ratio and voltage ratio
For power the decibel is 10 × log10 of the power ratio. For voltage or current across the same impedance it is 20 × log10 of the ratio, because power goes with the square. This page converts power levels only.
Related
dB to RatioDMS to Decimal DegreesScientific Notation ConverterPower ConverterConversion Centre
Frequently asked questions
How do I convert dBm to watts?
P (W) = 10^(dBm / 10) ÷ 1000. 30 dBm is 10³ mW, which is 1 W. 0 dBm is 1 mW.
How do I convert watts to dBm?
dBm = 10 × log10(P in mW). A power of 1 W is 1,000 mW, so it is 30 dBm. For dBW, use the power in watts directly: dBW = 10 × log10(P in W).
What is the difference between dBm and dBW?
They differ only in the reference power. dBm is relative to 1 milliwatt and dBW is relative to 1 watt, so dBW = dBm − 30.
Why does 3 dB mean double the power?
A change of 3 dB is a power ratio of 10^(3/10), about 1.995, so very nearly 2. Adding 10 dB multiplies the power by 10, and every 3 dB multiplies it by about 2.