Calculate RF gain, output power, or gain chain total from input power and stage gains, with results in dBm, dBW, watts, mW, or µW.
RF Gain Formula
The calculator uses three forms of the same power-ratio relationship, depending on which calculation mode you choose.
Gain from input and output power:
Output power from input and gain:
Cascaded gain chain:
- Pin: input (source) power, in dBm, dBW, W, mW, or µW
- 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 mode expresses both powers on the same logarithmic reference and subtracts the input level from the output level. The Output Power mode adds gain in dB to input power in dBm. The Gain Chain mode sums up to six entered stage gains or losses in dB, then applies that total to the starting power; enter at least one stage, with zero allowed. Output power is reported in dBm, dBW, W, mW, and µW. Negative stage values 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 | ≈0.50118723× | Approximately half power |
| 0 dB | 1× | Unity gain |
| 3 dB | ≈1.99526231× | Approximately double power |
| 10 dB | 10× | Illustrative 10× power gain |
| 20 dB | 100× | Illustrative 100× power gain |
| 30 dB | 1,000× | Illustrative 1,000× power gain |
| 60 dB | 1,000,000× | Illustrative 1,000,000× power gain |
| 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 at equal real impedances, use 20 × log10; RF gain on this page is power gain.
