Antenna Gain Calculator

Convert dBi ↔ dBd ↔ linear gain. Optional EIRP/ERP estimate using power + feedline loss.

How to Use

  1. Enter a gain value and choose its unit (dBi, dBd, or linear).
  2. Outputs update instantly (no uploads, no logins).
  3. (Optional) Enter TX power and feedline loss to estimate EIRP/ERP.
  4. Use Share Link only when you’re ready to save/share a configured state.

Gain Conversion

dBi, dBd, and linear gain (ratio).

Notes: 0 dBd ≈ 2.15 dBi. Linear gain is a power ratio (not percent).
Auto shows all outputs; Focus emphasizes one output for quick copy.

EIRP / ERP (Optional)

Estimate radiated power using TX power, losses, and antenna gain.

Enter transmitter output power before feedline loss.
Loss is subtracted in dB (or divided as a ratio).
If custom is selected, enter it below. Otherwise the top gain input drives EIRP/ERP.
Only used when “Custom” is selected above.
Outputs shown for both EIRP (isotropic) and ERP (dipole).
Show Work (step-by-step)
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Work uses base relationships (dB, ratios) and displays intermediate values for verification.

Reference

  • dBi is gain relative to an isotropic radiator (ideal point source).
  • dBd is gain relative to a half-wave dipole. Approx: dBi = dBd + 2.15.
  • Linear gain is a power ratio: G_linear = 10^(G_dB/10).
  • EIRP is effective isotropic radiated power; ERP is referenced to a dipole.

This tool is an idealized math model (no pattern nulls, polarization mismatch, VSWR return loss, or near-field effects).

FAQ

What is the difference between dBi and dBd?

dBi is referenced to isotropic; dBd is referenced to a half-wave dipole. A dipole is ~2.15 dB stronger than isotropic in its main lobe.

Does linear gain mean “times farther”?

No. Linear gain is a power ratio in a given direction. Range depends on link budget, environment, noise floor, and modulation.

Why does ERP differ from EIRP?

ERP is referenced to a dipole. Relationship: ERP(dBm) = EIRP(dBm) − 2.15.

Tool Info

Last updated:

Updates may include additional unit helpers (dBW), export formats, and edge-case validation improvements.