Queendom Tools

EIRP/ERP Calculator

For telecom technicians building or checking a point-to-point or sector link budget who need the EIRP the regulator and the link model actually reference — the radiated power at the antenna, not the radio's output — and need it in dBm, in watts, and as ERP against a half-wave dipole. EIRP (dBm) = transmitter power - cable and connector losses + antenna gain (dBi), with the ERP referred to a half-wave dipole (EIRP - 2.15 dB) and both in watts.

Calculate EIRP and ERP

Results

EIRP: 0.00 dBm (0.000 W)

ERP: 0.00 dBm (0.000 W)

Formula:

Disclaimer: For preliminary estimation only, not a substitute for review by a qualified/licensed engineer. EIRP (dBm) = transmitter power - cable and connector losses + antenna gain (dBi), with the ERP referred to a half-wave dipole (EIRP - 2.15 dB) and both in watts.

How to use this EIRP Calculator

  1. Enter the transmitter power and pick its unit — dBm for a radio datasheet figure, W for a PA output.
  2. Enter the cable loss in dB for the jumper/feeder run and the connector loss in dB for the terminations.
  3. Enter the antenna gain and choose dBi; if the datasheet quotes dBd, select dBd and the +2.15 conversion is applied for you.
  4. Read EIRP in dBm and W, and ERP in dBm and W, updating as you type.
  5. Optionally set antenna gain negative to model a lossy antenna and confirm the EIRP drops by that amount.

FAQ

Q: What is the formula for EIRP?
A: EIRP (dBm) = transmitter power (dBm) minus cable and connector losses plus antenna gain (dBi).

Q: What is the difference between EIRP and ERP?
A: ERP is referenced to a half-wave dipole instead of an isotropic radiator, so ERP = EIRP − 2.15 dB; this tool shows both.

Q: How do I convert an antenna gain quoted in dBd to dBi?
A: dBi = dBd + 2.15, and the calculator applies that conversion when you select dBd as the gain unit.

Q: How do I enter a transmitter power given in watts?
A: Select W as the power unit; the calculator applies P_dBm = 10 × log10(P_W × 1000), so 1 W becomes 30 dBm before the losses and gain are applied.