dBm / mW Converter

How it works

Power in mW = 10^(dBm/10). Conversely, dBm = 10 × log10(mW). The reference level is one milliwatt; dB without the m denotes a ratio rather than absolute power.

Worked example

−10 dBm is 0.1 mW; 0 dBm is 1 mW; 10 dBm is 10 mW. A 3 dB change is close to, but not exactly, a factor of two.

Inputs, edge cases & common mistakes

Zero or negative mW has no finite dBm value and is rejected. Negative dBm is valid and means power below 1 mW. Output is rounded for display; very small values use scientific notation.

Technical references

• NIST logarithmic quantities

Reviewed 9 September 2026. Found an issue? Send a correction with a reproducible example.