Point-to-point radio link calculator
What a link budget is
Simple bookkeeping in decibels: add up everything that adds to the signal (power, antenna gain) and subtract everything that eats it (cables, connectors, the path). If what is left at the receiver input exceeds its sensitivity, there will be a link.
| Frequency (MHz) | |
| Transmitter power (dBm) | |
| Transmitting end | |
| Antenna gain (dBi) | |
| Cable loss (dB) | |
| Connector loss (dB) | |
| Receiving end | |
| Antenna gain (dBi) | |
| Cable loss (dB) | |
| Connector loss (dB) | |
| Receiver sensitivity (dBm) | |
| Fade margin (dB) | |
| Result | |
| Maximum distance | |
| Free-space loss | |
| Signal level at the receiver input | |
| EIRP of the transmitting end | |
📐 The formulas
Free-space path loss (d in km, f in MHz):
FSPL = 20 × lg(d) + 20 × lg(f) + 32.44
The link budget:
Prx = Ptx + Gtx − L_tx + Grx − Lrx − FSPL
The maximum range from the fade margin:
FSPL_allowed = (total gain − path losses) − (sensitivity + margin)
d = 10^((FSPL_allowed − 20×lg(f) − 32.44) / 20)
EIRP — equivalent isotropically radiated power:
EIRP = Ptx + Gtx − transmit path losses
Symbols:
Ptx— transmitter power [dBm]Gtx,Grx— antenna gains [dBi]L— losses in cable and connectors [dB]- The fade margin is 10–20 dB, depending on climate and path length
Where this calculator stops:
- The formula assumes free space: line of sight, a clear Fresnel zone, no precipitation
- Rain and fog are not accounted for — at 5 GHz and above they add noticeable decibels
- Multipath and reflections from ground and water are not accounted for
- EIRP is limited by law: for Wi-Fi, check the regulations in force for your band
🎯 In practice
- Planning a link between two buildings or villages.
- Choosing antennas: you can see what going from 14 to 24 dBi buys.
- Judging the cable: a long thin run at 5 GHz eats more than the antenna gives.
Practical advice:
- Put the equipment near the antenna and run long Ethernet rather than long coax.
- A 10 dB margin is the minimum for a short path, 20 dB for a long one or one over water.
- The real range is also limited by line of sight: the budget may allow 40 km while the horizon allows only 20.
© 2026 UR3PKI · CyberDev.Space · Content licensed under CC BY-NC-SA 4.0.
How to cite this calculator
UR3PKI. «Point-to-point radio link calculator». CyberDev.Space. https://cyberdev.space/en/radio/calculators/others/wifi_bridge (licence CC BY-NC-SA 4.0).The licence lets you use this material freely, including in teaching materials, but only with attribution to the author and a link to the source.