dBm Adder (Power Sum) Calculator
Combine dBm values correctly, in milliwatts.
Your numbers
dBm
dBm
dBm
dBm
Your results
Combined power (dBm)
Combined power (dBm)
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Combined power (mW)
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Above the strongest signal (dB)
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dBm Adder (Power Sum) Calculator by TheCalcTools
How the dBm Adder (Power Sum) Calculator works
Enter the power of each signal in dBm.
Each is converted to milliwatts: P = 10^(dBm/10).
The milliwatts are added and converted back to dBm.
The formula
P_total = 10 log₁₀(Σ 10^(Pᵢ/10))
Worked example
Using the default values shown in the calculator:
| Power 1 (dBm) | -90 dBm |
|---|---|
| Power 2 (dBm) | -93 dBm |
| Power 3 (dBm; −200 to ignore) | -200 dBm |
| Power 4 (dBm; −200 to ignore) | -200 dBm |
- −90 dBm and −93 dBm add as 1.0e-9 mW + 5.0e-10 mW → -88.24 dBm.
- That is 1.76 dB above the strongest signal.
Result:
| Combined power (dBm) | -88.24 |
|---|---|
| Combined power (mW) | 1.501 × 10^-9 |
| Above the strongest signal (dB) | 1.76 |
Frequently asked questions
What does adding two equal signals give?
Two equal powers add 3 dB: −90 dBm plus −90 dBm = −87 dBm.
Can I subtract dBm values?
Subtract in milliwatts, not in dB. The difference of two dBm values is a ratio in dB, not a power.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.