Reference sheet
dBm power
Decibel-milliwatt to watts, and what each level means
dBm — power reference
dBm = 10·log₁₀(P / 1 mW) — every +10 dB is a ×10 in power, every +3 dB is roughly a ×2. Vrms assumes the standard 50 Ω RF/test-equipment impedance (audio and speaker lines are a different impedance, so don't reuse this column there). Common in RF and audio power specs.
| dBm | Power | Vrms (50 Ω) | What's around here |
|---|---|---|---|
| -100 dBm | 100 fW | 2.236 µV | Weak, often-unreliable Wi-Fi/LTE signal — near a typical receiver’s noise floor |
| -90 dBm | 1 pW | 7.071 µV | — |
| -80 dBm | 10 pW | 22.36 µV | — |
| -70 dBm | 100 pW | 70.71 µV | A solid, reliable Wi-Fi signal at ordinary indoor range |
| -60 dBm | 1 nW | 223.6 µV | — |
| -50 dBm | 10 nW | 707.1 µV | A very strong signal, close to the access point |
| -40 dBm | 100 nW | 2.236 mV | — |
| -30 dBm | 1 µW | 7.071 mV | A strong BLE/LoRa link at short range |
| -20 dBm | 10 µW | 22.36 mV | — |
| -10 dBm | 100 µW | 70.71 mV | — |
| -9 dBm | 125.9 µW | 79.34 mV | — |
| -6 dBm | 251.2 µW | 112.1 mV | — |
| -3 dBm | 501.2 µW | 158.3 mV | — |
| 0 dBm | 1 mW | 223.6 mV | 1 mW — a common BLE default transmit power |
| 3 dBm | 1.995 mW | 315.9 mV | +3 dB ≈ double the power of 0 dBm |
| 6 dBm | 3.981 mW | 446.2 mV | +6 dB ≈ 4× the power of 0 dBm |
| 9 dBm | 7.943 mW | 630.2 mV | +9 dB ≈ 8× the power of 0 dBm |
| 10 dBm | 10 mW | 707.1 mV | 10 mW — a typical Bluetooth Class 2 transmit power |
| 14 dBm | 25.12 mW | 1.121 V | A common LoRaWAN transmit-power ceiling in the EU868 band |
| 20 dBm | 100 mW | 2.236 V | 100 mW — a common Wi-Fi/LoRa transmit-power ceiling in many regions (check local rules) |
| 30 dBm | 1 W | 7.071 V | 1 W — near the top of what a hobbyist ISM-band transmitter is normally allowed (region-dependent) |
