EIRP Calculator
Calculate effective isotropic radiated power from transmit power, cable loss and antenna gain, and check it against regulatory limits.
Result
Working
- Formula
- EIRP = TX power - cable loss + antenna gain
- Calculation
- 20 - 1.5 + 19 = 37.5 dBm
- EIRP vs ERP
- ERP references a dipole and is 2.15 dB lower than EIRP for the same signal
Common regulatory limits (verify locally)
| Band / region | Typical EIRP limit | Notes |
|---|---|---|
| 2.4 GHz (EU) | 20 dBm | ETSI EN 300 328 - 100 mW EIRP |
| 2.4 GHz (US) | 36 dBm | FCC 15.247 point-to-multipoint |
| 5 GHz UNII-1 (EU) | 23 dBm | Indoor only, 200 mW EIRP |
| 5 GHz UNII-2 (EU) | 30 dBm | DFS and TPC required |
| 5 GHz UNII-3 (US) | 36 dBm | FCC point-to-multipoint |
| 5.8 GHz P2P (US) | 53 dBm | FCC allows higher EIRP for point-to-point |
| 6 GHz LPI | 30 dBm | Low power indoor, PSD limited |
About EIRP Calculator
EIRP is the power an ideal isotropic antenna would need to radiate to match what your antenna produces in its strongest direction. Regulators cap EIRP, not radio power - so a high-gain antenna forces the radio power down.
Power spectral density limits
Many regulators cap power spectral density rather than total EIRP, expressed in dBm per MHz. Because a wider channel spreads the same total power over more spectrum, a PSD limit permits more total EIRP on an 80 MHz channel than on a 20 MHz one — and conversely, narrowing a channel to improve link margin can put you over the PSD limit at unchanged total power. Check both figures before assuming a channel-width change is regulatory-neutral.
Gain is not free power
An antenna adds no energy; it concentrates it. A 19 dBi sector radiates the same total power as an omni but focuses it into a narrower beam, which is why EIRP rises. That focus is also why alignment matters so much: a few degrees off boresight on a high-gain dish can cost more than the gain was worth.
Common use cases
- Checking a sector or point-to-point install against local limits.
- Working out how far to turn radio power down after fitting a bigger antenna.
- Comparing two antenna options for the same site.
Edge cases and gotchas
- Limits differ by band, channel, indoor/outdoor and point-to-point versus multipoint - the table is a starting point, not authority.
- Many regulators also impose power spectral density limits, which bind before EIRP on wide channels.