liminfoLink Budget Calculator
Free web tool: Link Budget Calculator
Transmitter
Channel
Receiver
EIRP
21.00 dBm
Free Space Path Loss
100.05 dB
RX Power
-78.05 dBm
Link Margin
21.95 dB
Wavelength
12.49 cm
Max Distance (0dB margin)
12.51 km
About Link Budget Calculator
The Link Budget Calculator is a free, browser-based RF engineering tool that computes all key parameters of a wireless communication link in one place. Enter transmitter power (TX Power in dBm), transmit antenna gain (dBi), transmit cable loss (dB), carrier frequency, link distance, receive antenna gain (dBi), receive cable loss (dB), receiver sensitivity (dBm), and any additional losses. The calculator then computes EIRP (Effective Isotropic Radiated Power), free space path loss (FSPL) using the Friis transmission equation, received signal power (RX Power), link margin, signal wavelength, and maximum achievable distance at 0 dB margin.
RF engineers designing wireless sensor networks, FPV drone pilots verifying communication range, IoT developers deploying LoRa gateways, and telecommunications students learning link budget analysis will all benefit from this tool. Preset frequency bands cover the most common wireless standards: 433 MHz LoRa, 868 MHz LoRa (EU), 915 MHz LoRa (US), 2.4 GHz WiFi, 5 GHz WiFi, 5.8 GHz FPV, 28 GHz 5G millimeter-wave, and 60 GHz WiGig. Distance can be entered in meters, kilometers, or miles.
All calculations use the Friis free-space path loss formula: FSPL (dB) = 20·log₁₀(4πd/λ), where λ = c/f is the wavelength. EIRP = TX Power + TX Gain − TX Loss. RX Power = EIRP − FSPL + RX Gain − RX Loss − Other Loss. Link Margin = RX Power − RX Sensitivity. A positive link margin (shown in green) means the link is viable; negative (shown in red) means the link will fail. Maximum distance at 0 dB margin is extrapolated from the current link margin using the inverse square law relationship.
Key Features
- Computes FSPL using the Friis equation: FSPL = 20·log₁₀(4πd/λ) in dB
- Calculates EIRP = TX Power (dBm) + TX Antenna Gain (dBi) − TX Cable Loss (dB)
- Computes RX Power = EIRP − FSPL + RX Gain − RX Loss − Additional Loss
- Shows link margin (RX Power − RX Sensitivity) with green/red visual indicator for pass/fail
- Estimates maximum range at 0 dB margin using inverse square law scaling
- Preset frequency bands: 433 MHz, 868 MHz, 915 MHz (LoRa), 2.4 GHz, 5 GHz (WiFi), 5.8 GHz (FPV), 28 GHz (5G mmWave), 60 GHz (WiGig)
- Distance input supports meters, kilometers, and miles with automatic unit conversion
- Dark mode support and responsive sectioned layout for desktop, tablet, and mobile
Frequently Asked Questions
What is a link budget?
A link budget is a tabular or mathematical accounting of all signal gains and losses in a wireless communication link from transmitter to receiver. It is used to determine whether a wireless link will work reliably at a given distance and frequency, by verifying that the received signal power exceeds the receiver sensitivity by a sufficient margin.
What is free space path loss (FSPL)?
Free space path loss is the reduction in signal strength as electromagnetic waves propagate through free space. It is calculated as FSPL (dB) = 20·log₁₀(4πd/λ) = 20·log₁₀(4πdf/c), where d is distance, f is frequency, and c is the speed of light (299,792,458 m/s). FSPL increases by 6 dB every time the distance doubles, and by 20 dB per decade of frequency increase.
What is EIRP?
EIRP (Effective Isotropic Radiated Power) represents the total power radiated from an antenna in the direction of maximum gain, as if it were radiated by an ideal isotropic antenna. It is calculated as EIRP (dBm) = TX Power (dBm) + TX Antenna Gain (dBi) − TX Cable Loss (dB). EIRP is used as a standardized measure of transmitter and antenna effectiveness.
What is link margin and what value is considered good?
Link margin is the difference between the received signal power and the receiver sensitivity: Margin (dB) = RX Power − RX Sensitivity. A positive margin means the link can work. A margin of at least 10–20 dB is typically recommended in practice to account for fading, multipath, environmental changes, and hardware variations. The calculator shows the margin in green when positive and red when negative.
How does the maximum distance calculation work?
The maximum distance at 0 dB margin is estimated by scaling the current distance using the relationship that FSPL scales with 20·log₁₀(d). If the current link margin is M dB, the maximum distance is d_max = d × 10^(M/20). This assumes free-space conditions and no other loss changes.
What receiver sensitivity should I use for LoRa?
LoRa receiver sensitivity depends on the spreading factor (SF) and bandwidth. Typical values range from about −115 dBm at SF7 (125 kHz BW) to −137 dBm at SF12 (125 kHz BW). A commonly used value for range estimation is −130 dBm. Check your specific LoRa module datasheet for the exact sensitivity at your target configuration.
How does frequency affect link budget?
Higher frequencies experience more free-space path loss over the same distance. For example, a 5 GHz WiFi link has approximately 21 dB more path loss than a 433 MHz LoRa link at the same distance, due to the shorter wavelength. This is why LoRa at 433–915 MHz achieves much longer ranges than WiFi or 5G mmWave at equivalent transmit power.
What is the difference between antenna gain in dBi and dBd?
dBi (decibels relative to an isotropic radiator) measures antenna gain relative to a theoretical point source that radiates equally in all directions. dBd (decibels relative to a dipole) measures gain relative to a half-wave dipole, which itself has about 2.15 dBi of gain. To convert: dBi = dBd + 2.15. This calculator uses dBi, which is the more common specification in datasheets.