dBm — Decibels Relative to One Milliwatt

dBm (decibel-milliwatts) is a unit of absolute power expressed on a logarithmic scale referenced to one milliwatt. The conversion is: P(dBm) = 10 · log₁₀(P / 1 mW). By definition, 0 dBm = 1 mW, 10 dBm = 10 mW, 20 dBm = 100 mW, and 30 dBm = 1 W. Negative values represent power below 1 mW: −30 dBm = 1 µW, −60 dBm = 1 nW, and so on.

The logarithmic scale is convenient because RF systems span an enormous dynamic range. A cellular tower may transmit at +40 dBm (10 W) while a phone receives the signal at −90 dBm (10⁻¹² W) — a factor of 10¹³, far easier to track in dB than in linear units.

In telecommunications, dBm is used to specify transmit power, receive sensitivity, and signal strength along a path. Wi-Fi access points typically transmit at +15 to +23 dBm. Smartphones receive cellular signals at −50 dBm (very strong) to −110 dBm (near the noise floor). Broadcast TV transmitters can operate above +90 dBm (1 megawatt).

Because dBm is a logarithmic unit, addition in dB corresponds to multiplication in linear units. A 3 dB increase doubles power; a 10 dB increase multiplies it by ten. Loss along a path is added as negative dB or subtracted from the source power. This is why link budgets — the bookkeeping of every gain and loss between transmitter and receiver — are universally done in decibels.

dBm is distinct from dB, which is dimensionless and expresses a ratio between two powers. dBm always refers to an absolute power level relative to 1 mW.

RADIHALT designs EMF protection blankets built around woven copper-nickel Faraday fabric. The terminology on this page — from Faraday-cage physics through attenuation figures and ICNIRP exposure limits — is what underpins the engineering and the claims we publish about our products.

We try to keep our marketing language tied to the same vocabulary regulators and physicists use. If a definition on this page conflicts with anything on a RADIHALT product page, the glossary entry is the source we hold ourselves to.