Enter the input and output power levels in dBm into the calculator to determine the Rf gain. The gain is calculated in decibels (dB).
RF Gain Formula
The calculator uses three forms of the same power-ratio relationship, depending on which tab you pick.
Gain from input and output power:
Gain (dB) = 10 * log10(Pout / Pin)
Output power from input and gain:
Pout (dBm) = Pin (dBm) + Gain (dB)
Cascaded gain chain:
Gtotal (dB) = G1 + G2 + G3 + ... + Gn
- Pin: input (source) power, in dBm, dBW, mW, or W
- Pout: output power after the device or chain
- Gain (dB): logarithmic power ratio; positive means amplification, negative means loss
- Linear gain: ratio Pout/Pin, related to dB by 10^(dB/10)
- G1...Gn: gain or loss of each stage in the signal chain
The Gain tab converts both powers to milliwatts, takes the ratio, and converts to dB. The Output Power tab adds the gain (in dB) to the input power expressed in dBm and reports the result in dBm, mW, W, and dBW. The Gain Chain tab sums every stage value in dB, then applies that total to the starting power. Negative numbers in the chain represent losses such as cable, filter, or connector attenuation.
Reference Tables
Use these to sanity-check inputs and outputs before running the calculation.
| dB | Linear ratio | Meaning |
|---|---|---|
| -20 dB | 0.01× | Heavy attenuation |
| -10 dB | 0.1× | Pad or long cable run |
| -3 dB | 0.5× | Half power |
| 0 dB | 1× | Unity gain |
| 3 dB | 2× | Double power |
| 10 dB | 10× | Typical low-noise amp |
| 20 dB | 100× | Driver amplifier |
| 30 dB | 1,000× | Power amplifier stage |
| 60 dB | 1,000,000× | Full receiver chain |
| Power | dBm | dBW |
|---|---|---|
| 1 µW | -30 dBm | -60 dBW |
| 1 mW | 0 dBm | -30 dBW |
| 10 mW | 10 dBm | -20 dBW |
| 100 mW | 20 dBm | -10 dBW |
| 1 W | 30 dBm | 0 dBW |
| 10 W | 40 dBm | 10 dBW |
| 100 W | 50 dBm | 20 dBW |
Worked Examples
Example 1: Single amplifier. An amplifier accepts -20 dBm and delivers 5 dBm. Gain = 5 - (-20) = 25 dB. The linear ratio is 10^(25/10) ≈ 316×.
Example 2: Receive chain. A signal arrives at -65 dBm. It passes through 2 dB of cable loss, an LNA with 18 dB gain, a filter with 1.5 dB loss, and a second amplifier at 12 dB. Total gain = -2 + 18 - 1.5 + 12 = 26.5 dB. Output = -65 + 26.5 = -38.5 dBm.
FAQ
Why does subtracting dBm values give dB? dBm is a power level referenced to 1 mW. When you subtract two dBm values, the reference cancels and you are left with a pure ratio in dB.
Can gain be negative? Yes. A negative dB value means the device or path attenuates the signal. Cables, splitters, and pads all produce negative gain.
Does this account for noise figure or compression? No. The calculator handles linear, small-signal power gain only. Once an amplifier reaches its 1 dB compression point, actual output will fall below the value predicted here.
How do I convert linear gain to dB by hand? Use 10 × log10(ratio). A 2× ratio is about 3 dB, 10× is exactly 10 dB, and 100× is 20 dB. For voltage ratios you would use 20 × log10, but RF gain on this page is power gain.
