dBm to Watts Converter

Power in radio systems is almost always expressed in dBm (decibels relative to 1 milliwatt) because the numbers span many orders of magnitude and gain/loss calculations become simple addition and subtraction.

Formulas:

• dBm to Watts: P(W) = 10^(dBm/10) / 1000
• Watts to dBm: dBm = 10 × log₁₀(P in milliwatts) = 10 × log₁₀(P_watts × 1000)

Key reference points:

• 0 dBm = 1 mW
• +10 dBm = 10 mW
• +20 dBm = 100 mW
• +30 dBm = 1 W
• +37 dBm = 5 W (handheld radio)
• +40 dBm = 10 W
• +47 dBm ≈ 50 W
• +50 dBm = 100 W (typical HF transceiver)
• +53 dBm ≈ 200 W
• +60 dBm = 1,000 W (1 kW amplifier)
• −100 dBm = 0.1 pW (weak signal reception)
• −120 dBm = 1 fW (typical receiver noise floor)

Why dBm is useful: A 100W transmitter (+50 dBm) loses 100 dB in free space, then gains 10 dBi from a directional antenna, giving a −40 dBm received signal. All addition and subtraction, no multiplying at all. That is the entire appeal, and it is why every link budget in radio is written this way.

dBm and dBW: subtract 30 from a dBm figure to get dBW, decibels relative to one watt. Satellite and broadcast engineering usually quotes dBW; amateur and RF test gear usually quotes dBm. A 100 W transmitter is +50 dBm and +20 dBW, and both describe the same 100 watts.

dBi vs dBd: Antenna gain in dBi is relative to an isotropic radiator. dBd is relative to a dipole. dBi = dBd + 2.15.