Link Budget Calculator
Find received signal power, free-space path loss, and link margin for a radio link from transmit power, antenna gains, frequency, and distance.
📡 What is a Link Budget?
A link budget is an accounting of every gain and loss a radio signal experiences on its way from transmitter to receiver, used to predict whether a wireless link will actually work. It combines transmit power and antenna gains with free-space path loss (FSPL), the unavoidable spreading loss over distance, and any other implementation losses, to arrive at the received signal power.
RF and wireless engineers use link budgets to plan point-to-point microwave links, satellite communication, Wi-Fi and cellular coverage, and any radio system where range and reliability matter, checking whether the predicted received power leaves enough margin above the receiver's sensitivity to work reliably even with some real-world signal degradation.
A common point of confusion is treating a link budget calculation as a guarantee. Free-space path loss assumes a perfectly clear, unobstructed line-of-sight path, real-world links experience additional loss from obstructions, multipath, atmospheric absorption, and fading, which is exactly why designers target a healthy positive margin rather than a link that just barely closes on paper.
This calculator computes free-space path loss from your frequency and distance, the resulting received power, and the link margin against your receiver's sensitivity, plotting how received power falls off with distance and where it crosses the sensitivity floor.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — 2.4 GHz Point-to-Point Link
Pt = 30 dBm, Gt = 15 dBi, Gr = 10 dBi, f = 2400 MHz, d = 5 km, Lother = 2 dB, Rx sensitivity = -90 dBm
Example 2 — Long-Range 900 MHz Link
Pt = 43 dBm, Gt = 20 dBi, Gr = 20 dBi, f = 900 MHz, d = 20 km, Lother = 3 dB, Rx sensitivity = -100 dBm
Example 3 — Marginal 5.8 GHz Link (Link Fails)
Pt = 20 dBm, Gt = 6 dBi, Gr = 6 dBi, f = 5800 MHz, d = 1 km, Lother = 1 dB, Rx sensitivity = -75 dBm
❓ Frequently Asked Questions
🔗 Related Calculators
What is a link budget?
A link budget is an accounting of all the gains and losses a radio signal experiences from transmitter to receiver, used to predict whether a wireless link will work reliably. It combines transmit power, antenna gains, path loss, and other losses to find the received power, then compares that against the receiver's sensitivity.
What is the formula for received power in a link budget?
Pr = Pt + Gt + Gr - FSPL - Lother, where Pt is transmit power, Gt and Gr are the transmit and receive antenna gains, FSPL is free-space path loss, and Lother covers cable, connector, and other implementation losses, all in decibels or dBm.
What is free-space path loss (FSPL)?
FSPL is the loss a radio signal experiences purely from spreading out over distance in free space, with no obstructions, reflections, or atmospheric effects. It is given by FSPL(dB) = 20log10(d_km) + 20log10(f_MHz) + 32.44, increasing with both distance and frequency.
Why does path loss increase with frequency?
For a fixed antenna gain, higher-frequency signals have a shorter wavelength and effectively a smaller capture area at the receiving antenna, this is captured mathematically in the FSPL formula's dependence on frequency, higher frequency signals experience more path loss for the same distance and antenna gain.
What is link margin and why does it matter?
Link margin is the difference between received power and the receiver's sensitivity threshold (the minimum signal power it can reliably detect). A positive margin means the link closes with room to spare, a margin of zero or negative means the link may fail or perform unreliably, especially once real-world fading and interference are considered.
Does this calculator account for real-world obstructions and fading?
No, this calculator computes free-space path loss only, assuming a clear line-of-sight path with no obstructions, reflections, multipath, or atmospheric absorption. Real-world links, especially non-line-of-sight or long-distance terrestrial ones, need additional loss and fade margin beyond what FSPL predicts.
What is receiver sensitivity?
Receiver sensitivity is the minimum signal power (in dBm) a receiver needs to demodulate a signal reliably at an acceptable error rate, it depends on the receiver's noise figure, bandwidth, and modulation scheme, and is typically found in the specific radio or modem's datasheet.
How much does doubling the distance affect path loss?
Doubling distance adds exactly 20log10(2), about 6.02 dB, to free-space path loss, and doubling frequency adds the same 6.02 dB. This makes FSPL a useful quick mental-math tool: every distance or frequency doubling costs about 6 dB of link margin.
What should be included in the 'other losses' term?
Lother should include cable and connector losses between the radio and antenna, any polarization mismatch loss, atmospheric or rain attenuation for the specific frequency and path, and any design implementation margin, everything the free-space and antenna-gain terms do not already capture.
What units does this calculator use?
Transmit power and receiver sensitivity are entered in dBm, antenna gains and other losses in dB, frequency in megahertz, and distance in kilometers. Received power, path loss, and link margin results are all shown in decibels or dBm.