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How do you calculate a wireless link budget?

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A link budget accounts for every gain and loss between transmitter and receiver: Pr = Pt − Ltx + Gt − Lpath − Lmisc + Gr − Lrx (all in dB), and the link margin is Pr minus the receiver sensitivity. Antenna gains, efficiencies, polarization and mismatch all enter directly.[1][2]

  1. Transmitter output power (dBm).
  2. Cable, connector and matching losses at the transmitter.
  3. Transmit antenna realized gain toward the receiver (dBi).
  4. Path loss plus excess losses (walls, foliage, rain, diffraction).
  5. Polarization mismatch and body loss.
  6. Receive antenna realized gain and receive-side losses.
  7. Receiver sensitivity, derived from −174 dBm/Hz + 10·log10B + NF + required SNR.
  8. Fade margin for multipath and shadowing.[2][3]

What does a worked example look like?

A 915 MHz link: Pt = 20 dBm, cable 1 dB, Gt = 2 dBi, Gr = 0 dBi (compact antenna with −2 dB efficiency included), FSPL at 2 km ≈ 97.7 dB, 10 dB excess loss. Pr ≈ 20 − 1 + 2 − 97.7 − 10 + 0 = −86.7 dBm. With a sensitivity of −120 dBm the margin is about 33 dB.

How much margin is enough?

Fixed line-of-sight links commonly plan 10–20 dB or more depending on availability, rain region and fading; mobile links need larger fade margins or diversity; satellite links use availability-based rain margins from ITU-R P.618.[4][2]

Frequently asked questions

Does antenna efficiency belong in the link budget?

Yes; use realized gain, which includes efficiency and mismatch.

What is receiver sensitivity?

The minimum input power for a specified error rate.

How much does 6 dB of margin buy?

About double the free-space range.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

  1. “A Note on a Simple Transmission Formula”. H. T. Friis, Proceedings of the IRE, vol. 34, no. 5, pp. 254-256. May 1946.
  2. “Antennas and Propagation for Wireless Communication Systems, 2nd ed.”. S. R. Saunders and A. Aragón-Zavala, Wiley. 2007.
  3. “Wireless Communications, 2nd ed.”. A. F. Molisch, Wiley. 2011.
  4. “Recommendation ITU-R P.618: Propagation data and prediction methods required for the design of Earth-space telecommunication systems”. ITU-R. current edition.
Categories: Propagation