A 100 mW radio output
10 log₁₀(100) = 20 dBm. This is the radio output power, not necessarily the EIRP after its cable loss and antenna gain.
Power level relative to 1 mW 20 dBm Open in the calculator
dBm to mW and watts converter
Enter a power in any one of the three units. Negative dBm values are valid: −30 dBm is one microwatt.
You enterCalculated
relative to 1 mW
milliwatts
watts
-68.05 dBm is 156.6 pW.
Drag the cursor along the rule, nudge it by 3 or 10 dB, or edit the boxed value. Every 10 dB is ten times the power; every 3 dB about twice.
Power level relative to 1 mW
-68.05dBm
Check the values to see a result.
- Milliwatts
- 1.566e−7 mW
- Watts
- 1.566e−10 W
Negative dBm means less than 1 mW, not negative physical power. A dB gain or loss is a ratio, not an absolute power.
How it’s calculated
- PdBm = 10 log₁₀(PmW)=10 log₁₀(1.566e-7)=-68.05 dBm
- PmW = 10^(PdBm / 10)=10^(-68.05 / 10)=1.566e-7 mW
- PW = PmW / 1000=1.566e-7 / 1000=1.566e-10 W
dBm = 10 log₁₀(mW)mW = 10^(dBm / 10)W = mW / 1,000
-68.05 dBm = 1.566e-7 mW = 1.566e-10 W.
Tip: A 10 dB increase multiplies power by ten. A 3 dB increase is approximately a doubling.
Convert absolute power, not a ratio
dBm expresses power relative to one milliwatt. Zero dBm is 1 mW, 20 dBm is 100 mW and 30 dBm is 1 W. A negative value represents a positive power below 1 mW: −30 dBm is 0.001 mW, or 0.000001 W.
From dBm
mW = 10^(dBm / 10)
Divide the dBm value by ten and use it as the exponent of ten. The result is in milliwatts. Divide by 1,000 to obtain watts.
To dBm
dBm = 10 log₁₀(mW)
First convert watts to milliwatts if needed. The logarithm takes a positive power relative to 1 mW. Zero watts has no finite dBm value and negative physical power is outside this conversion.
Power gain and loss
Power ratio = 10^(dB / 10)
A 10 dB gain multiplies power by ten. A 3 dB gain multiplies it by about 1.995, close to two. A 3 dB loss divides by the same factor. These are relative changes; dB alone does not identify an absolute power.
dBm, milliwatts and watts examples
A −90 dBm received signal
A -90 dBm signal: 10^(−90 / 10) = 0.000000001 mW, equal to 0.000000000001 W, or one picowatt. Negative dBm does not mean a negative number of watts.
Power level relative to 1 mW -90 dBm Open in the calculator
dBm to mW and W conversion table
Common radio, sensor and test levels, from received signals near the noise floor to transmitter outputs.
| Power (dBm) | Milliwatts (mW) | Watts (W) |
|---|---|---|
| −120 | 1 × 10⁻¹² | 1 × 10⁻¹⁵ |
| −110 | 1 × 10⁻¹¹ | 1 × 10⁻¹⁴ |
| −100 | 1 × 10⁻¹⁰ | 1 × 10⁻¹³ |
| −90 | 1 × 10⁻⁹ | 1 × 10⁻¹² |
| −80 | 1 × 10⁻⁸ | 1 × 10⁻¹¹ |
| −70 | 1 × 10⁻⁷ | 1 × 10⁻¹⁰ |
| −60 | 1 × 10⁻⁶ | 1 × 10⁻⁹ |
| −50 | 1 × 10⁻⁵ | 1 × 10⁻⁸ |
| −40 | 0.0001 | 1 × 10⁻⁷ |
| −30 | 0.001 | 1 × 10⁻⁶ |
| −20 | 0.01 | 1 × 10⁻⁵ |
| −10 | 0.1 | 0.0001 |
| −3 | 0.5012 | 0.0005012 |
| 0 | 1 | 0.001 |
| 3 | 1.995 | 0.001995 |
| 5 | 3.162 | 0.003162 |
| 7 | 5.012 | 0.005012 |
| 10 | 10 | 0.01 |
| 13 | 19.95 | 0.01995 |
| 14 | 25.12 | 0.02512 |
| 17 | 50.12 | 0.05012 |
| 20 | 100 | 0.1 |
| 23 | 199.5 | 0.1995 |
| 25 | 316.2 | 0.3162 |
| 27 | 501.2 | 0.5012 |
| 30 | 1,000 | 1 |
| 33 | 1,995 | 1.995 |
| 36 | 3,981 | 3.981 |
| 40 | 10,000 | 10 |
| 43 | 19,953 | 19.95 |
| 47 | 50,119 | 50.12 |
| 50 | 100,000 | 100 |
| 60 | 1,000,000 | 1,000 |
Questions about dBm, milliwatts and watts
Is 0 dBm no signal?
No. It is exactly 1 mW. Zero watts approaches negative infinity dBm and has no finite result in this calculator.
Can I add two dBm power values?
Convert each to watts or milliwatts, add the powers where that physical model applies, then convert the total back. Two equal independent 1 mW powers total 2 mW, approximately 3.0103 dBm. Phase-coherent signals require their own treatment.
Why is there no voltage conversion?
A voltage needs an impedance and an RMS convention before it determines power. This tool converts power units only. For power ratios use 10 log₁₀; the familiar 20 log₁₀ voltage ratio applies under the appropriate equal-impedance assumptions.
Limits of this result
- This converts absolute power only. It does not convert field strength, antenna gain, RSSI quality or a legal transmit limit.
- Enter a positive linear power. Zero power corresponds to negative infinity dBm and is outside this finite-number calculator.