dBm ↔ W Conversion Table (Power Reference)
Reference table of mW and W values from −40 dBm to +60 dBm in 5 dB steps, with the values worth memorizing and the mistakes people make.
dBm is an absolute power level referenced to 1 mW. Signal generator output, amplifier ratings and receiver input are all handled in dBm, so conversion to watts comes up constantly. The table below runs from −40 dBm to +60 dBm in 5 dB steps; use the calculator for values in between.
Power conversion table (5 dB steps)
| dBm | mW | W |
|---|---|---|
| -40 | 1×10⁻⁴ | 1×10⁻⁷ |
| -35 | 3.16×10⁻⁴ | 3.16×10⁻⁷ |
| -30 | 0.001 | 1×10⁻⁶ |
| -25 | 0.003162 | 3.16×10⁻⁶ |
| -20 | 0.01 | 1×10⁻⁵ |
| -15 | 0.03162 | 3.16×10⁻⁵ |
| -10 | 0.1 | 1×10⁻⁴ |
| -5 | 0.3162 | 3.16×10⁻⁴ |
| 0 | 1 | 0.001 |
| 5 | 3.162 | 0.003162 |
| 10 | 10 | 0.01 |
| 15 | 31.62 | 0.03162 |
| 20 | 100 | 0.1 |
| 25 | 316.2 | 0.3162 |
| 30 | 1000 | 1 |
| 35 | 3162 | 3.162 |
| 40 | 10000 | 10 |
| 45 | 31620 | 31.62 |
| 50 | 100000 | 100 |
| 55 | 316200 | 316.2 |
| 60 | 1×10⁶ | 1000 |
Open the calculator → dBm ↔ Watt Power Converter
Formula
P(mW) = 10^(P(dBm) / 10)
P(dBm) = 10·log₁₀(P(mW))
Worth memorizing
- 0 dBm = 1 mW (the reference)
- 30 dBm = 1 W
- Every +10 dB is ×10 power, every +3 dB is roughly ×2
- −3 dB is about half, −10 dB is one tenth
Common mistakes
- Using 20·log₁₀ for power. Power uses 10·log₁₀; voltage, current and field strength use 20·log₁₀.
- Mixing up dBm and dB. dBm is an absolute level, dB is a ratio. "20 dBm of gain" is wrong; it should be "20 dB".
- Treating rated output and the 1 dB compression point (P1dB) as the same. Base immunity test levels on P1dB to keep the waveform clean.
- Reading amplifier output without subtracting cable loss. Power into the antenna is the output minus cable and connector losses.
Related calculators
Results and summaries are for reference. For certification and test reports use the latest official standard text and calibrated instrument data. Last updated: 2026-10-10