RF Link Budget Calculator
Use this RF Link Budget Calculator to estimate EIRP, free space path loss (FSPL), received power, link margin, and a simple pass or fail result for wireless links.
It is useful for RF engineering, microwave links, Wi-Fi bridges, cellular planning, lab validation, and general wireless system design when you need a quick first-pass budget before moving into more detailed propagation or interference analysis.
The goal is practical: help you answer whether a link is likely to close, how much margin you have, and whether the basic RF budget looks reasonable before you spend time on field testing, deeper propagation modelling, or technology-specific radio analysis.
Calculate RF Link Budget
Result
Enter the RF system values to calculate the link budget.
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How to read the result
| Output | What it tells you | Why it matters |
|---|---|---|
| EIRP | The effective transmitted power after antenna gain and transmitter-side losses. | This is the practical launch power seen by the path, not just the raw transmitter output. |
| FSPL | The basic geometric path loss caused by frequency and distance in free space. | It is the baseline propagation loss before you add walls, foliage, connectors, fade margin, or other penalties. |
| Received Power | The estimated power at the receiver input after path loss and receive-side gains/losses. | This is the quickest way to judge whether the link is comfortably above sensitivity or already too weak. |
| Link Margin | The gap between received power and receiver sensitivity. | A positive margin means the link is theoretically decodable. A larger margin usually means better robustness. |
| Pass / Fail | Whether the margin still meets the required fade margin target. | This gives a fast engineering decision point for planning or troubleshooting. |
What each input means
| Input | What it represents | What engineers should watch for |
|---|---|---|
| Tx Power | The conducted output power at the transmitter before antenna gain and losses. | Do not confuse conducted power with EIRP. Regulatory limits often apply to EIRP, not raw transmitter power. |
| Tx / Rx Antenna Gain | The directional gain of the transmitting and receiving antennas. | Use realistic installed gain values. Real-world mounting, tilt, and beam direction affect how much of this gain is actually useful. |
| Cable and Other Losses | Losses from feeder cables, connectors, jumpers, filters, duplexers, radomes, or implementation overhead. | These small losses add up quickly. Underestimating them is one of the most common reasons a paper budget looks better than field performance. |
| Frequency | The carrier frequency used by the link. | Higher frequencies generally increase free-space path loss and may also bring stricter propagation penalties in the real world. |
| Distance | The RF path length between transmitter and receiver. | This calculator assumes a simple line-of-sight free-space relationship. Terrain, clutter, and indoor environments can make the real path effectively much worse. |
| Receiver Sensitivity | The minimum receive power needed for the intended modulation, coding, and performance target. | Sensitivity depends on bandwidth, data rate, modulation, coding, and receiver design. Use the right value for the actual mode you care about. |
| Additional Path Losses | Extra attenuation beyond ideal free-space loss. | Use this for building penetration, foliage, rain, polarization mismatch, body loss, or other known penalties that your base FSPL estimate misses. |
| Required Fade Margin | The design margin you want above minimum sensitivity. | This is the difference between a barely working link and a robust one. Availability-driven designs often need meaningful margin, not just a positive link budget. |
RF Link Budget Formula
EIRP (dBm) = Tx Power + Tx Antenna Gain - Tx Cable Loss - Other Tx Losses
FSPL (dB) = 32.44 + 20 * log10(f_MHz) + 20 * log10(d_km)
Received Power (dBm) = EIRP - FSPL - Additional Path Losses + Rx Antenna Gain - Rx Cable Loss - Other Rx Losses
Link Margin (dB) = Received Power - Receiver Sensitivity
Pass if Link Margin >= Required Fade Margin
How engineers typically use this calculator
- Planning: estimate whether a proposed RF link has enough margin before deployment.
- Troubleshooting: compare expected received power with measured field values when the link underperforms.
- Backhaul and microwave work: check whether antenna gains and cable losses still leave enough usable margin.
- Wi-Fi or private network design: validate point-to-point and point-to-multipoint assumptions quickly.
- Cellular engineering: use it as a first-pass RF budget before moving to technology-specific tools like the 5G NR link budget calculator.
Worked example
Suppose you want to evaluate a simple 2.4 GHz wireless link with the following assumptions:
- Tx power: 30 dBm
- Tx antenna gain: 15 dBi
- Tx cable loss: 2 dB
- Distance: 1 km
- Rx antenna gain: 15 dBi
- Rx cable loss: 2 dB
- Receiver sensitivity: -80 dBm
The rough interpretation is:
- EIRP is high enough to support a practical outdoor link budget.
- FSPL is driven mainly by the 2.4 GHz carrier and the 1 km distance.
- Received power should remain comfortably above sensitivity if no large extra losses are present.
- If the real link performs worse than this estimate, the gap often comes from obstruction, interference, polarization mismatch, connector loss, or alignment problems rather than the basic free-space budget alone.
Common engineering mistakes
- Mixing conducted power and EIRP: transmitter output power alone is not the same as radiated power at the antenna.
- Ignoring feeder and connector losses: a few dB of overlooked loss can erase the margin of a marginal link.
- Using the wrong sensitivity number: receiver sensitivity changes with bandwidth, modulation, coding, and target error performance.
- Assuming FSPL is the whole story: clutter, diffraction, penetration, rain, foliage, and interference often dominate the real link.
- Designing with zero or tiny margin: a link that barely closes on paper is usually fragile in operation.
Do you need advanced inputs?
No. For many first-pass RF checks, the basic inputs are enough to estimate EIRP, FSPL, received power, and link margin.
Use the advanced inputs when you want a more realistic design check. That is especially helpful when you need to include connector or implementation loss, radome loss, foliage, atmospheric attenuation, penetration effects, or a required fade margin for availability planning.
Troubleshooting with the calculator
This tool is also useful when a live RF link underperforms. Start by comparing the calculated received power and link margin with what the real system reports. If the theoretical budget looks healthy but the deployed link still fails, the gap usually points to conditions outside an ideal free-space model.
- If the calculated margin is negative: the link is fundamentally too weak unless gain, losses, distance, or sensitivity assumptions change.
- If the calculated margin is barely positive: the link may work intermittently but will usually be fragile under fading or changing conditions.
- If the calculated margin is strong but performance is poor: inspect interference, misalignment, polarization issues, congestion, implementation loss, or non-line-of-sight effects.
- If field measurements are much worse than expected: verify cable loss, connector condition, antenna direction, installed gain, and path obstructions.
When this calculator is not enough
This tool is intentionally a first-pass RF budget calculator. It does not replace full propagation modelling, clutter modelling, interference analysis, multipath analysis, or technology-specific schedulers and receiver behavior.
If you are working on a 5G-specific radio problem, the 5G NR Link Budget Calculator is usually a better next step. If you only need a basic path-loss estimate, the Free Space Path Loss Calculator is the simpler companion tool.
If you are validating a cellular radio workflow, the next useful references are often NR-ARFCN and band planning, 5G coverage troubleshooting, and 5G low throughput troubleshooting.