dBm to Watts Calculator
dBm
Power1.000000 W
Power1,000.0000 mW
The dBm to Watts Calculator converts radio-frequency power between the logarithmic dBm scale and linear watts. dBm expresses power relative to one milliwatt, which makes wide ranges of transmitter and receiver levels easy to read, but circuit math needs real watts. Switch the mode to go either way: enter a dBm level to get watts and milliwatts, or enter watts to get the equivalent dBm.
Formula
P(W) = 0.001 × 10^(dBm / 10); dBm = 10 × log10(P / 0.001)
- P
- Power in watts
- dBm
- Power level in decibels relative to one milliwatt
- 0.001
- One milliwatt, the dBm reference power, in watts
How it works
- Choose a direction with the mode switch: dBm to watts, or watts to dBm.
- For dBm to watts the calculator raises ten to the power of the dBm divided by ten to get milliwatts, then divides by 1000 for watts.
- For watts to dBm it divides the power by one milliwatt and takes ten times the base-ten logarithm of that ratio.
Worked example
Converting a 33 dBm transmitter output to watts.
- Milliwatts = 10^(33 / 10) = 10^3.3 = 1995.26 mW.
- Watts = 1995.26 ÷ 1000 = 1.995262 W.
33 dBm equals about 1.995262 W (roughly 2 W).
Frequently asked questions
- What does 0 dBm mean?
- Zero dBm is exactly one milliwatt, the reference for the scale. Every 10 dBm increase multiplies power by ten, and every 3 dBm increase roughly doubles it.
- Why is RF power measured in dBm instead of watts?
- Radio links span enormous ranges, from watts at a transmitter to picowatts at a receiver. The logarithmic dBm scale compresses that span into manageable numbers and turns gains and losses into simple addition and subtraction.
- Can power in dBm be negative?
- Yes. Any power below one milliwatt is negative in dBm; for example -30 dBm is one microwatt. Negative dBm values are normal for received signals.
- Why must watts be positive to convert to dBm?
- The conversion takes the logarithm of the power ratio, and the logarithm is only defined for positive numbers. Zero or negative power has no dBm value, so the calculator requires a positive input.