Link Budget Calculator predicts received signal power across an RF link by combining transmitter power, antenna gains, cable losses, free-space loss, and misc. propagation losses.
Link Budget Calculator: Predicting Received RF Signal Power Across a Wireless Link
This tool calculates received signal power at the far end of an RF link by adding transmitter gains and subtracting every loss between the transmitter and receiver. RF, wireless, satellite, and ham radio engineers use it to confirm a link will deliver enough signal above the noise floor before hardware is deployed.
How to Use
Enter transmitter power, transmit antenna gain, transmit-side losses, free-space loss, miscellaneous losses, receive antenna gain, and receive-side losses. The calculator returns received power, EIRP/ERP, carrier-to-noise density, and the equivalent RMS/peak voltage across a 50-ohm receiver.
Formula
The core equation is the standard RF link budget formula used throughout satellite and wireless communications engineering (documented, for example, in Dennis Roddy’s Satellite Communications and in ITU-R propagation guidance for the free-space term): gains are added and losses are subtracted, all in dB/dBm.
$$P_{RX} = P_{TX} + G_{TX} – L_{TX} – L_{FS} – L_{M} + G_{RX} – L_{RX}$$
Effective radiated power references the transmit side only:
$$EIRP = P_{TX} + G_{TX} – L_{TX}$$
ERP restates that figure against a half-wave dipole reference instead of an isotropic radiator, using the standard 2.15 dB isotropic-to-dipole gain offset from antenna theory:
$$ERP = EIRP – 2.15$$
Carrier-to-noise density compares received power against the thermal noise floor at the standard reference temperature $T_0 = 290\text{K}$, where $N_0 = kT_0 \approx -174$ dBm/Hz:
$$C/N_0 = P_{RX} – N_0$$
$P_{RX}$ is also converted to a linear power and then to RMS/peak voltage across a 50-ohm load: $P_{lin} = 10^{(P_{RX}-30)/10}$ W, $V_{rms} = \sqrt{P_{lin} \times 50}$, $V_{peak} = V_{rms}\sqrt{2}$. The most common input mistake is entering losses as negative numbers when the calculator already subtracts them — doing both cancels the loss out or doubles it instead of applying it once.
$C/N_0$ is carrier power divided by noise density, not by total noise power, so it doesn’t depend on receiver bandwidth. Two links can show an identical $C/N_0$ here and still deliver very different actual SNR and data rate once bandwidth is applied — that conversion ($C/N = C/N_0 – 10\log_{10}(BW)$) happens outside this calculator and is easy to skip by mistake.
Reference Table
| Constant | Value | Used for |
|---|---|---|
| Thermal noise floor ($kT_0$) | -174 dBm/Hz | Carrier-to-noise density at $T_0 = 290$K reference |
| Isotropic-to-dipole gain offset | 2.15 dB | Converting EIRP to ERP |
FAQ
What’s the difference between EIRP and ERP?
EIRP references an isotropic radiator; ERP references a half-wave dipole, which already has 2.15 dBi of gain over isotropic. ERP is always 2.15 dB lower than EIRP for the same transmitter.
Why is C/N₀ independent of bandwidth?
C/N₀ compares carrier power to noise power per hertz, not total noise power. Total noise scales with bandwidth, so C/N (an SNR) requires subtracting $10\log_{10}(\text{bandwidth})$ from C/N₀ separately.
Why is my received power lower than expected?
Check the sign of every loss entered. If losses were typed in as negative values, the calculator’s subtraction turns them positive again, silently doubling the penalty instead of applying it once.
Does a positive received power guarantee the link works?
No. What matters is the margin between received power and receiver sensitivity, not the raw number. A high positive value with a high-sensitivity requirement can still fail the link.
Does this calculator check regulatory EIRP limits?
No. It reports the physics only. Many license-exempt bands cap EIRP (for example 36 dBm in parts of the 2.4 GHz band); a mathematically valid result here can still exceed what regulations allow.