EIRP & ERP Calculator
Build a conducted-to-radiated power ledger with dBi/dBd conversion and directional context.
- Typical inputs
- Conducted power, feed and mismatch losses, antenna gain in dBi/dBd, and direction.
- Calculated output
- Delivered antenna power, EIRP, ERP, watts, and a signed dB ledger.
- Model status
- Release D · documented and numerically tested
What radiated reference level follows from delivered power, loss, mismatch, and antenna gain?
Conducted-to-radiated ledger
Name the conducted-power plane. Feed and mismatch loss remain separate from direction-specific antenna gain; EIRP and ERP are reference quantities, not total radiated power.
0.000 dBm→ −0.00 dB feed→ −0.00 dB mismatchAntenna input
0.000 dBm→ +2.15 dBiEIRP
2.150 dBm
- Power at antenna input
- 0.000000 dBm · -30.000000 dBW 1 mW
- EIRP
- 2.150000 dBm · -27.850000 dBW 1.64059 mW
- ERP
- 0.000000 dBm · -30.000000 dBW 1 mW
- Gain converted to dBi
- 2.150000 dBi
- Reference conversion
- EIRP = ERP + 2.15 dB
This is not a regulatory pass/fail result. Jurisdiction, service, band, bandwidth, mode, averaging, duty cycle, direction, and date determine applicable limits.
What this calculator is doing
Feed and mismatch loss subtract from conducted power, then directional antenna gain adds. dBd converts to dBi with the stated 2.15 dB reference difference.
How to read the result
Use the correct direction, duty cycle, service definition, and reference plane. Check current local rules separately; this is not a compliance decision.
Equations & conventions
- EIRP references an isotropic radiator; ERP references a half-wave dipole.
- Antenna gain is directional and excludes separately entered feed loss.
- Loss fields are positive dB magnitudes.
Independently checked example
Checked example: 0 dBm delivered to an ideal 2.15 dBi antenna gives 2.15 dBm EIRP and 0 dBm ERP.
Common mistakes
- Treating dBi and dBd as interchangeable.
- Calling transmitter connector power EIRP.
- Assuming good impedance match guarantees radiation efficiency.
- Treating antenna gain as created power.
- Adding 2.15 dB in the wrong reference direction or double-counting feed loss.
Assumptions, validity & omissions
- Gain applies in the stated direction.
- Feed and mismatch losses are not already embedded in gain.
- This is not a regulatory compliance determination.
Sources & model provenance
- Recommendation ITU-T K.91 (01/2024) (opens in a new tab) — EIRP/ERP definitions, feeder loss, and 2.15 dB reference conversion. Accessed 2026-09-05.