Convert optical or RF power between dBm and watts (or milliwatts).
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.
dBm to milliwatts
mW = 10^(dBm / 10)
Milliwatts to dBm
dBm = 10 × log10(mW)
0 dBm equals 1 mW, which equals 0.001 W (1 x 10⁻³ watts).
30 dBm = 10^(30/10) = 1000 mW = 1 watt — a useful reference point, since every 10 dB step is a 10x power multiple.
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.
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.