dBm to Watt
Convert optical or RF power between dBm and watts (or milliwatts).
About dBm to Watt
dBm expresses power on a logarithmic scale referenced to 1 milliwatt. Converting dBm to linear power uses mW = 10^(dBm/10), and the reverse conversion uses dBm = 10·log10(mW). Watts and milliwatts are related by a simple factor of 1000. This three-way converter is useful across both RF and optical power measurements, since both domains commonly specify power in dBm for the same reasons — compact representation and additive loss/gain math.
Formulas
dBm to milliwatts
mW = 10^(dBm / 10)
Milliwatts to dBm
dBm = 10 × log10(mW)
Worked example
With the default values below, dBm to Watt returns dBm of 0.000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Input Unitone of dBm, Milliwatts (mW), Watts (W)
- dBm
- Value
- 0
Results
- dBm
- 0.000 dBm
- Milliwatts
- 1.000000 mW
- Watts
- 0.001000000 W
Step by step
- 1Values used
- 2dBm to milliwatts
- 3Milliwatts to dBm
- 4dBm= 0.000 dBm
- 5Milliwatts= 1.000000 mW
- 6Watts= 0.001000000 W
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 9 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
What is 0 dBm in watts?
0 dBm equals 1 mW, which equals 0.001 W (1 x 10⁻³ watts).
What is 30 dBm in watts?
30 dBm = 10^(30/10) = 1000 mW = 1 watt — a useful reference point, since every 10 dB step is a 10x power multiple.
Why does optical power use the same dBm unit as RF power?
Both domains benefit from the same logarithmic convenience — optical link budgets add/subtract losses in dB just like RF link budgets, so representing absolute optical power in dBm (referenced to 1 mW) keeps the same additive math working across a fiber optic path.
How much does +3 dB correspond to in linear power?
Roughly double — +3 dB is approximately a 2x increase in linear power (mW or W), and -3 dB is approximately a 50% decrease, a handy rule of thumb frequently used in quick link-budget estimates.