dBi to dBm Calculator (via EIRP)
You cannot directly convert antenna gain (dBi) into power (dBm) without a reference power. This tool uses standard RF link-budget equations to calculate either EIRP or required transmitter power.
EIRP (dBm) = Tx Power (dBm) + Antenna Gain (dBi) - System Loss (dB)
How to convert dBi to dBm correctly
A common RF question is: “How do I convert dBi to dBm?” The key point is that these units represent different things:
- dBi = antenna gain relative to an isotropic antenna.
- dBm = absolute power level referenced to 1 milliwatt.
Because one is gain and the other is power, there is no one-step standalone conversion. You must include at least one power reference, such as transmitter output power or target EIRP.
When this calculator is useful
1) Finding legal transmit settings
Many wireless regulations limit EIRP instead of raw radio output. If you know your antenna gain, this calculator tells you how much transmitter power you can use while staying compliant.
2) Planning Wi-Fi, LTE, LoRa, and point-to-point links
In practical deployment, your radio output, antenna gain, and line losses all impact the signal that is actually radiated. This tool gives you quick, repeatable numbers for link-budget planning.
3) Back-solving transmitter power
If you have a required EIRP target and selected antenna hardware, the calculator can back-calculate required dBm at the radio port.
Quick example
Suppose your access point outputs 20 dBm, antenna gain is 8 dBi, and cable loss is 2 dB.
EIRP = 20 + 8 - 2 = 26 dBm
26 dBm is approximately 398 mW (about 0.398 W).
Common mistakes to avoid
- Trying to convert dBi to dBm with no power baseline.
- Forgetting cable and connector losses.
- Mixing dBd and dBi (they are not the same reference).
- Assuming high antenna gain always means more transmitter power is allowed by regulation.
Reference values
| dBm | mW | W |
|---|---|---|
| 0 dBm | 1 mW | 0.001 W |
| 10 dBm | 10 mW | 0.01 W |
| 20 dBm | 100 mW | 0.1 W |
| 30 dBm | 1000 mW | 1 W |
| 36 dBm | 3981 mW | 3.98 W |
Final takeaway
A “dBi to dBm converter” is really an RF power calculator that combines gain and losses with a known power reference. Use this page to calculate EIRP or back-calculate transmitter output in seconds, with clear equations and consistent units.