Case 1
- Power level (dBm)
- 30dBm
1.000000W
Open with these valuesdBm to Watts Calculator
1.000000W
Result: 1.000000 WdBm counts decibels above one milliwatt, so 0 dBm is 1 mW and 30 dBm is 1 W. Every 10 dB multiplies the power by ten and every 3 dB roughly doubles it. Negative values are normal — a Wi-Fi signal arriving at −67 dBm is 0.2 nanowatts, not an error.
Worked examples
Case 2
- Power level (dBm)
- 20dBm
0.100000W
Open with these valuesCase 3
- Power level (dBm)
- -10dBm
0.000100W
Open with these valuesHow it's calculated
P(W) = 10^(dBm ÷ 10) ÷ 1000
- StepEnter the level in dBm; a minus sign is allowed and common.
- ResultRead the power in watts. Multiply by 1000 for milliwatts.
Reference table
| Level (dBm) | Same power in mW | Power (W) |
|---|---|---|
| −10 | 0.1 mW | 0.000100 |
| 0 | 1 mW — the reference point | 0.001000 |
| 10 | 10 mW | 0.010000 |
| 20 | 100 mW | 0.100000 |
| 30 | 1000 mW, that is 1 W | 1.000000 |
| 43 | 19952.6 mW | 19.952623 |
Questions
What does dBm mean?
Decibels relative to one milliwatt. 0 dBm is 1 mW, 10 dBm is 10 mW and 30 dBm is 1 W. Because the scale is logarithmic, negative values are perfectly valid — they just mean less than a milliwatt, which is normal for a received Wi-Fi or cellular signal.
How do I convert dBm to watts?
P(W) = 10^(dBm ÷ 10) ÷ 1000. Raise ten to the power of the level divided by ten to get milliwatts, then divide by a thousand for watts. For 30 dBm: 10^3 = 1000 mW = 1 W.
What is the difference between dBm and dBW?
The reference, and nothing else. dBm counts from one milliwatt, dBW from one watt, and since a watt is a thousand milliwatts the offset is always exactly 30 dB: dBW = dBm − 30. So 30 dBm, 0 dBW and 1 W are three names for the same power.
Why does +10 dBm mean ten times the power?
Because dBm is defined as 10 × log₁₀(P ÷ 1 mW), so P = 10^(dBm ÷ 10) mW. Each extra 10 dB adds one to the exponent, which multiplies the power by ten. Adding 3 dB roughly doubles it, since 10^0.3 is about 2.
What is a good Wi-Fi signal strength in dBm?
About −30 dBm is as good as it gets, right beside the router. Around −67 dBm is the usual floor for reliable HD video, −70 dBm still carries browsing, and near −90 dBm the signal is lost in the noise. All of these are fractions of a microwatt.
Sources and last check
Information, not professional advice.