Link Budget Calculator
The formula
What the received signal tells you
The full Friis ledger from transmit watts to the dBm landing on the receiver, against a −90 dBm sensitivity reference.
Calculation: FSPL = 32.44 + 20log(d_km) + 20log(f_MHz); Prx = Tx+G−FSPL−losses. Enter your inputs and every substitution is shown below the result.
Reading the result
The margin column is the whole design conversation: every tree, rainstorm and future interference source gets paid out of it.
Rules of thumb: Aim ≥ 20 dB margin for licensed-link SLAs; 10 dB for best-effort.
Limitations and best practice
Real clutter adds 6–20 dB that pure FSPL ignores — urban NLoS budgets should run the model twice with losses.
This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Frequently asked questions
Why subtract 2 dB?
Does antenna height fix a negative margin?
Source & methodology
Friis transmission equation in dB form (32.44 constant).
Link Budget explained: formula, worked example and honest limits
Budgets fail on the numbers nobody wrote down — this tool forces every one of them into the open. Searchers land on a Link Budget page for three reasons — to plan, to compare options, and to check that somebody else’s arithmetic is honest. This tool serves all three, and everything after the calculator explains the model instead of hiding it.
In plain terms, Link Budget answers the question "Received power?". The measurement matters because it converts a situation that feels complicated — several inputs pulling in different directions — into a single number you can act on. Within Technology & Computing, Networks & Storage is the context where this figure is quoted most often, and professionals treat it as a first-pass screen rather than a verdict.
That makes documentation a feature. The steps block above exists so that the next engineer to read this page can verify not just the result but the reasoning — the difference between a number that gets acted on and one that gets argued with.
Nothing below is stock text pasted around a number: the worked example computes received power = -71.6 dBm from this tool’s own defaults, and the sensitivity section ranks the inputs that move the result — TX power first, at ≈3.2 % of the headline for a ten-percent error either way in that input. Read the sections in order and you will be able to reproduce every figure by hand.
The Link Budget formula, explained
One formula, published in full: FSPL = 32.44 + 20log(d_km) + 20log(f_MHz); Prx = Tx+G−FSPL−losses. Anything you can read, you can reproduce in a spreadsheet, and that reproducibility is the whole point of printing it rather than hiding it behind a button.
TX power (dBm) (example value 23) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Replace the example with the figure from your own records — the tool recomputes instantly and the printed steps follow your numbers.
TX antenna (dBi) (example value 6) is a measured number in the unit named by the label; the formula does not convert for you. This input feeds the formula directly; a defensible figure here is worth more than false precision anywhere else.
RX antenna (dBi) (example value 8) is a quantity rather than a category — precision here is cheap and worth having. This input feeds the formula directly; a defensible figure here is worth more than false precision anywhere else.
Distance (km) (example value 2) is a quantity rather than a category — precision here is cheap and worth having. Measure twice and use the unit the label asks for — length terms often scale the result geometrically.
Frequency (MHz) (example value 2,541) is a measured number in the unit named by the label; the formula does not convert for you. If you are unsure what belongs in this field, look at the printed steps: the substitution shows exactly how the engine uses it.
The default Link Budget calculation, written out in full
Rather than describe the calculation, here it is end to end — every substitution in order, starting from the inputs above. Starting figures: TX power (dBm), TX antenna (dBi), RX antenna (dBi), Distance (km). The computed received power comes out at -71.6 dBm, which the interpretation band labels “Workable at mid rates”.
- FSPL = 32.44 + 20 log(2.0) + 20 log(2,541) = 106.6 dB
- Prx = 23 + 6 + 8 − 106.6 − 2 = -71.6 dBm
- Margin over −90 dBm = 18.4 dB
- With the same antennas the limit distance is 16.71 km
Free-space path loss — 106.6 dB. Read next to the headline, this is the figure that shows the shape of the trade-off.
Margin over −90 dBm sensitivity — 18.4 dB. This is the number experienced users quote when the headline alone would mislead.
Max distance at this sensitivity — 16.71 km. If your inputs change, this is usually the first companion figure to move.
System noise allowance spent — 2 dB. If your inputs change, this is usually the first companion figure to move.
Re-running with your own figures is instant; re-running by hand once is the best way to know the tool is telling you the truth.
How far Link Budget can reasonably move
The honest version of any estimate is a corridor, and this one is cheap to produce: Link Budget was recomputed at 5 points along the dominant input, with every other field left untouched.
| TX power setting | Received power |
|---|---|
| 80 % of the example value | -76.2 dBm |
| 90 % of the example value | -73.9 dBm |
| example inputs | -71.6 dBm |
| 110 % of the example value | -69.3 dBm |
| 120 % of the example value | -67.0 dBm |
That spread — -76.2 dBm at the low end, -67.0 dBm at the high — is what a careful read of Link Budget looks like: a band you can state out loud, with the reason for each edge. Reproduce it in the form above by editing TX power alone; the substitution steps will follow your figures exactly.
The levers behind Link Budget, ranked by effect
This list was computed for this specific engine just now: each numeric input was nudged ±10 % while every other field held its example value, and the received power was recalculated from scratch. It is the fastest honest answer to “what matters most in Link Budget?” — and it is specific to these defaults, because sensitivity moves with the starting point.
- Nudge TX power by ±10 % and Link Budget lands between -73.9 dBm and -69.3 dBm (sensitivity ≈3.2 %)
- Distance +10 % → Link Budget = -72.4 dBm · −10 % → -70.6 dBm (the received power shifts ≈1.3 %)
- Nudge Frequency by ±10 % and Link Budget lands between -72.4 dBm and -70.6 dBm (sensitivity ≈1.3 %)
- RX antenna: ten percent up gives -70.8 dBm, ten percent down gives -72.4 dBm — ≈1.1 % of the received power either way
- Nudge TX antenna by ±10 % and Link Budget lands between -72.2 dBm and -71.0 dBm (sensitivity ≈0.8 %)
TX power is the dominant lever here: ten percent either way moves the result by about 3.2 %, from -73.9 dBm to -69.3 dBm. That is where a careless figure does the most damage, so check it against a source, and treat Distance as the second priority (≈1.3 % per ten percent). The remaining fields can sit at safe defaults without materially changing the answer — knowing which is which is what separates a careful calculation from an anxious one.
Interpreting the Link Budget verdict
Nobody acts on a bare figure — they act on a figure with a comparison attached. On the example inputs the band reads “Workable at mid rates”; your own figures place you on a different rung of the same ladder. How much of that band is luck? On TX power alone ten percent either way covers -73.9 dBm to -69.3 dBm. The practical reading rules: compare against your own history before comparing against other people; treat band boundaries as zones, not walls — one point on the wrong side of a threshold rarely changes a real outcome; and when a companion output contradicts the headline, believe the pair.
Placing this figure in context: calculators of this kind differ less in arithmetic than in what they choose to ignore. This one keeps TX power (dBm) explicit so that the omissions are visible rather than hidden in a preset.
The errors that quietly break a Link Budget figure
Real clutter adds 6–20 dB that pure FSPL ignores — urban NLoS budgets should run the model twice with losses. This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Reporting the headline and quietly discarding Free-space path loss. The companions are where the shape of the trade-off survives the rounding.
Attention is also misallocated between fields. Having measured this engine, we can say where it belongs: TX power first, everything else second.
Another is comparing across contexts: a Link Budget computed with one set of conventions should never be lined up against a figure computed with another. Check the inputs behind both before ranking them.
A quick check for any Link Budget figure
- Confirm the example values are plausible for your own situation before replacing them.
- Check that every field the formula needs actually arrived from a document, not from recollection.
- Re-verify TX power against a source document — ten percent of error there moves the headline by ≈3.2 %.
- Recompute once with the dominant input deliberately set low, and see whether the decision changes.
- Verify each input against its original source document, not memory.
- Confirm the answer against one independent method or published benchmark for Link Budget.
Five steps from raw inputs to a figure you can defend
Using a calculator well sounds trivial, but the difference between a decision-grade figure and a throwaway one lives entirely in the routine. The routine for Link Budget takes a minute to learn and applies to every input above.
Step 1 — one document, one pass. Open the statement, label or record that holds tx power (dbm), tx antenna (dbi), rx antenna (dbi), distance (km), frequency (mhz) and transcribe straight into the form. Transcription from a single source removes the mismatch errors that appear when figures are assembled from three different places. Precision is a promise you make about your data; make sure your inputs can keep it.
Step 2 — compute the version you would not be embarrassed by. If a stranger audited your inputs, which set would you hand over? Enter that set, read the result, and treat everything else as upside. Precision is a promise you make about your data; make sure your inputs can keep it.
Step 3 — play with the inputs on purpose. Ten percent up, ten percent down, one field at a time. Within a few minutes you will know this calculation better than most people who quote its results. Precision is a promise you make about your data; make sure your inputs can keep it.
Step 4 — run the scenario trio. Expected, pessimistic, optimistic. The gap between pessimistic and expected is the number to plan against; the optimistic result is useful only as a ceiling. When two sources disagree, it is almost never the arithmetic that differs.
Step 5 — write the one-line memo. “Received power = -71.6 dBm on this date, from these inputs.” That line is the entire deliverable; everything else on this page is how you earned the right to write it. Say the answer out loud before you save it; if it sounds wrong, the model did not change, your understanding did.
From calculation to decision: where Link Budget earns its keep
Most Networks & Storage disagreements are arithmetic disagreements in disguise. When Received power of -71.6 dBm sits on the table with its working shown, the conversation stops being about who sounds more confident and starts being about which input is wrong. Re-running a number costs seconds; retracting a decision costs considerably more.
Used properly this is a five-minute filter that saves weeks. Compute Link Budget, reject what fails, and only then bring in the expensive analysis for the survivors. Estimates improve most when the worst case is written down in ink.
Treat Link Budget like a smoke alarm rather than a painting — its value is in being tested periodically, not in being admired once. Comparisons are cheap: run the identical calculation for the alternative and look at the gap.
People also ask about Link Budget
What affects Link Budget the most?
Link Budget is driven above all by TX power. Perturbing only that field by ten percent either way produced -69.3 dBm against the -71.6 dBm baseline — a ≈3.2 % response, while Distance manages ≈1.3 %.
Which matters more: distance or tx power?
For Link Budget, TX power wins the head-to-head (≈3.2 % against ≈1.3 % per ten-percent change). Knowing which input dominates is the difference between careful work and merely slow work.
What is a typical Link Budget?
There is no honest universal average for Link Budget, but there is a reference point: the defaults on this page produce -71.6 dBm (Workable at mid rates). Replace the inputs with your own and compare — that comparison is the useful meaning of “typical”.
How do I calculate Link Budget by hand?
Use the stated model — FSPL = 32.44 + 20log(d_km) + 20log(f_MHz); Prx = Tx+G−FSPL−losses — and substitute in the order the tool prints (it starts from FSPL = 32.44 + 20 log(2.0) + 20 log(2,541) = 106.6 dB). On the example inputs the hand route lands on -71.6 dBm, exactly what the calculator shows. A spreadsheet reproduces it in two or three cells; doing it once by hand is what makes the automated answer trustworthy.
What happens to Link Budget if tx power changes by 10 %?
The engine was re-run with that field moved by ten percent while everything else stayed fixed: the received power goes across -73.9 dBm to -69.3 dBm, a swing of roughly 3.2 % around the -71.6 dBm baseline. That ratio is the practical definition of how much this input matters.
Is the Link Budget result of -71.6 dBm good or bad?
The tool answers “what”, not “whether”: -71.6 dBm carries the verdict “Workable at mid rates” for the default case, which is a starting interpretation rather than a verdict on your situation. Re-run with your own figures and compare the bands.
Can Link Budget be negative or empty?
Yes, and that is informative rather than broken: a negative Link Budget usually means the inputs encode an outflow or a shortfall, and the verdict band above labels exactly that situation instead of hiding it.
Is Link Budget accurate?
The arithmetic is exact: FSPL = 32.44 + 20log(d_km) + 20log(f_MHz); Prx = Tx+G−FSPL−losses is evaluated with full floating-point precision and every substitution is printed in the worked example. What limits accuracy is input quality and the model’s assumptions, so treat the -71.6 dBm result as the correct answer to the question you typed — and check the assumptions section before acting on it.
Why subtract 2 dB?
A standing system-noise/connector allowance — standard budget hygiene; replace it with measured feedline loss when known.
Does antenna height fix a negative margin?
Only by restoring line-of-sight and Fresnel clearance — worth 10–25 dB in clutter, which is exactly what FSPL under-priced.
Does this Link Budget tool store my numbers?
No. The entire calculation runs in your browser session; nothing entered above is transmitted or saved, which is the correct behaviour for sensitive Technology & Computing figures and the reason you can re-run this page as often as you like.
Key terms on this page
- Free-space path loss
- 106.6 dB on the example inputs — a companion figure printed beside the headline of Link Budget so that no result is read in isolation.
- Margin over −90 dBm sensitivity
- 18.4 dB on the example inputs — a companion figure printed beside the headline of Link Budget so that no result is read in isolation.
- Max distance at this sensitivity
- 16.71 km in the default Link Budget calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Received power
- The primary output of this tool: -71.6 dBm for the default inputs, computed exactly from FSPL = 32.44 + 20log(d_km) + 20log(f_MHz); Prx = Tx+G−FSPL−losses.
- Worked example
- Every substitution in order, from the example inputs to -71.6 dBm — the audit trail for the headline figure.
- Verdict band
- The plain-language label — here “Workable at mid rates” — mapping the computed figure onto experience-based ranges for Technology & Computing.
- Sensitivity (±10 %)
- How far the Link Budget moves when a single input is nudged ten percent either way; the ranked list on this page is computed live from this engine.
The provenance of this Link Budget calculation
The model is published arithmetic implemented exactly as written: FSPL = 32.44 + 20log(d_km) + 20log(f_MHz); Prx = Tx+G−FSPL−losses. Source of record: Friis transmission equation in dB form (32.44 constant). Any other implementation of this model should return the same figure for the same inputs. If one does not, the difference is in its assumptions — which this page prints and that one probably does not.
Treat the output as a precise answer to the question you typed: exact arithmetic, transparent formula, published source, no hidden rounding. The promise to the reader is narrow and testable: same inputs, same output, no silent rounding, and no figure presented without the formula that produced it.
Next steps after the calculation
Add the costs the estimate omits first — fees, waste, contingency — then re-run before treating the figure as a budget line.
Whoever you are (planners sizing a spend before committing money), the next step is the same: replace the example inputs with your own, note the date, and re-run whenever a figure moves. In Technology & Computing, a dated figure is a trend, and an undated one is a rumour.