Watts to dBm Calculator
Convert between watts, milliwatts, and dBm (decibel-milliwatts) for RF, telecom, and audio power level calculations.
Convert Watts ↔ dBm
Enter power in watts or dBm to convert in either direction.
How to Convert Watts to dBm
dBm (decibel-milliwatts) is a logarithmic unit of power relative to 1 milliwatt. To convert watts to dBm: dBm = 10 × log₁₀(P in mW). To convert from dBm to watts: W = 10^(dBm/10) / 1000.
dBm to Watts Reference Table
| dBm | Watts | Milliwatts | Application |
|---|---|---|---|
| -30 dBm | 0.000001 W | 0.001 mW | Very weak signal |
| -10 dBm | 0.0001 W | 0.1 mW | Weak WiFi signal |
| 0 dBm | 0.001 W | 1 mW | Reference level |
| 10 dBm | 0.01 W | 10 mW | Bluetooth, low-power RF |
| 20 dBm | 0.1 W | 100 mW | WiFi router, cell phone |
| 30 dBm | 1 W | 1,000 mW | Strong WiFi AP, walkie-talkie |
| 40 dBm | 10 W | 10,000 mW | Ham radio, cell tower |
| 50 dBm | 100 W | 100,000 mW | FM radio station |
Key dBm Rules of Thumb
- +3 dBm = double the power: 0 dBm (1 mW) + 3 dB = 3 dBm (2 mW)
- +10 dBm = 10× the power: 20 dBm (100 mW) + 10 dB = 30 dBm (1 W)
- −3 dBm = half the power: 30 dBm (1 W) − 3 dB = 27 dBm (0.5 W)
- 0 dBm = 1 milliwatt: The reference point for all dBm measurements
Frequently Asked Questions About dBm Power Levels
What is dBm?
dBm (decibel-milliwatts) is a logarithmic unit expressing power relative to 1 milliwatt. 0 dBm = 1 mW. Positive dBm means more than 1 mW; negative dBm means less. It is used in RF engineering, fiber optics, and telecommunications because it simplifies gain/loss calculations to addition and subtraction.
Why use dBm instead of watts?
dBm uses a logarithmic scale that compresses the enormous range of power levels in RF systems. A WiFi signal may range from 0.000001 mW (−30 dBm) to 1,000 mW (+30 dBm) — a billion-fold range. In dBm, this is simply −30 to +30, making calculations easier.
What is a good WiFi signal in dBm?
−50 dBm is excellent, −60 dBm is good, −70 dBm is fair, −80 dBm is weak, and −90 dBm is barely usable. Most devices need at least −70 dBm for reliable connectivity. Stream video needs −65 dBm or better.
How do I convert dBm to watts?
Watts = 10^(dBm/10) / 1000. For 23 dBm: W = 10^(23/10) / 1000 = 10^2.3 / 1000 = 199.5 / 1000 = 0.2 W (200 mW).
What is the difference between dBm and dB?
dBm is an absolute power measurement (referenced to 1 mW). dB is a relative ratio between two values. "This signal is 20 dBm" tells you the actual power (100 mW). "This amplifier has 20 dB gain" tells you it multiplies power by 100×, but not the actual output level.