Antenna Gain Calculator
The formula
What the antenna eirp tells you
Turns transmit power, antenna gain and feeder loss into the one number regulators and link budgets both read: effective isotropic radiated power.
Calculation: EIRP = tx − loss + gain; directivity ≈ 41000/(az×el); range factor = 10^(dB/20). Enter your inputs and every substitution is shown below the result.
Reading the result
Every +6 dB roughly doubles the usable link distance; most legal limits are written in EIRP, not watts.
Rules of thumb: Home APs: 2–5 dBi omni (EIRP ~20 dBm); CPE panels 14–19 dBi; dish links 24–34 dBi.
Limitations and best practice
Gain is a trade: the narrow beam that adds 12 dBi also misaligns 3° off target. Mount stiffly or lose more than you gained.
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
Does higher gain always help?
What about dBd vs dBi?
Source & methodology
IEEE antenna theory 41000/(az×el) directivity approximation; EIRP = Pt−Lr+Gt definition.
Antenna Gain: what this tool answers
This page was written for one job: turning your own inputs into a defensible figure, with the working shown. Searchers land on an Antenna Gain 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.
The useful way to hold Antenna Gain is as a ratio with a story attached: EIRP = tx − loss + gain; directivity ≈ 41000/(az×el); range factor = 10^(dB/20) says how the parts combine, and the 46.5 dBm figure above is simply that sentence written in numbers. Everything that follows unpacks one clause of the sentence at a time.
What makes Antenna Gain worth calculating is not precision but position: it tells you which side of a threshold you are on, and by how much. A rough figure that settles the direction beats an elaborate one that never commits.
Nothing below is stock text pasted around a number: the worked example computes effective radiated power = 46.5 dBm from this tool’s own defaults, and the sensitivity section ranks the inputs that move the result — Transmitter power first, at ≈6.5 % of the headline for a ten-percent error either way in that input — which is the thread the rest of this guide pulls on.
Every input in Antenna Gain, and what it does to the answer
One formula, published in full: EIRP = tx − loss + gain; directivity ≈ 41000/(az×el); range factor = 10^(dB/20). 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.
Transmitter power (dBm) (example value 30) 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.
Antenna gain (dBi) (example value 18) is a plain measured quantity — the unit shown in the label is the unit the formula expects. If you are unsure what belongs in this field, look at the printed steps: the substitution shows exactly how the engine uses it.
Cable + connector loss (dB) (example value 2) 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.
Beamwidth (degrees) (example value 68) 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.
The default Antenna Gain calculation, written out in full
The tool prints its own working; this is the same arithmetic on the example values, reproduced so you can follow it by hand. Starting figures: Transmitter power (dBm), Antenna gain (dBi), Cable + connector loss (dB), Beamwidth (degrees). Run to the end, the effective radiated power resolves to 46.5 dBm — Point-to-multipoint strong (check licensing) on the bands this tool uses.
- After cable: 30.0 − 1.5 = 28.5 dBm at the antenna
- EIRP = 28.5 + 18.0 = 46.5 dBm
- Beamwidth 68° ⇒ directivity ≈ 8.9 dBi (41000 rule)
- Same tx, this antenna multiplies reach by 6.68×
EIRP in milliwatts — 44,668.4 mW. This is the number experienced users quote when the headline alone would mislead.
Assumed symmetric beam directivity — 8.9 dBi. Read next to the headline, this is the figure that shows the shape of the trade-off.
Range factor vs isotropic — 6.68 ×. This is the number experienced users quote when the headline alone would mislead.
Power after cable — 28.5 dBm. Compare it against the main result of 46.5 dBm before drawing conclusions.
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.
The Antenna Gain corridor: your result across a realistic band
Read this table as the practical error bar on the headline figure. It answers the question people actually have after seeing a single number: how wrong could this be if the main input is off by ten or twenty percent?
| Transmitter power setting | Effective radiated power |
|---|---|
| 80 % of the example value | 40.5 dBm |
| 90 % of the example value | 43.5 dBm |
| example inputs | 46.5 dBm |
| 110 % of the example value | 49.5 dBm |
| 120 % of the example value | 52.5 dBm |
The corridor runs from 40.5 dBm to 52.5 dBm across that band — which is the range worth planning inside rather than the single 46.5 dBm point estimate. Reproduce it in the form above by editing Transmitter power alone; the substitution steps will follow your figures exactly.
The levers behind Antenna Gain, 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 effective radiated power was recalculated from scratch. For Antenna Gain the ranking is measured rather than guessed, and it belongs to these defaults: shift the starting point and the order can shift with it.
- Nudge Transmitter power by ±10 % and Antenna Gain lands between 43.5 dBm and 49.5 dBm (sensitivity ≈6.5 %)
- Antenna gain: ten percent up gives 48.3 dBm, ten percent down gives 44.7 dBm — ≈3.9 % of the effective radiated power either way
- Nudge Cable + connector loss by ±10 % and Antenna Gain lands between 46.4 dBm and 46.7 dBm (sensitivity ≈0.3 %)
Transmitter power is the dominant lever here: ten percent either way moves the result by about 6.5 %, from 43.5 dBm to 49.5 dBm. That is where a careless figure does the most damage, so check it against a source, and treat Antenna gain as the second priority (≈3.9 % per ten percent). The rest of the inputs earn only a rounding-error of attention, and that asymmetry is the practical payoff of measuring rather than asserting.
Reading the result: bands, zones and thresholds
The value above only becomes useful the moment you know what it is being measured against. On the example inputs the band reads “Point-to-multipoint strong (check licensing)”; your own figures place you on a different rung of the same ladder. The sensitivity list shows how far a modest input error moves you along that ladder: for Transmitter power, ±10 % covers 43.5 dBm to 49.5 dBm. The practical reading rules: ask what would have to change to move you one band. If the answer is “a small, plausible input difference”, the band itself is not the finding — the uncertainty is.
Related measures answer related questions, and the distinctions matter: Antenna Gain is the quantity, Effective radiated power is this tool’s reading of it, and the decision that follows belongs to neither of them separately.
Why Antenna Gain results go wrong — and how to prevent it
Gain is a trade: the narrow beam that adds 12 dBi also misaligns 3° off target. Mount stiffly or lose more than you gained. 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.
Comparing an Antenna Gain computed here with a figure from another source that uses different conventions. Same name, different denominator — the disagreement is usually in the definitions, not the data.
One mistake is specific to this engine: assuming every input matters equally. The computation above shows Transmitter power dominating — a careful figure there beats false precision everywhere else.
A final trap is presentation: reporting Antenna Gain to more decimal places than the inputs support. The tool prints what the arithmetic gives; you should quote only what your least precise field justifies.
A quick check for any Antenna Gain figure
- Validate inputs against a live measurement, not datasheet peak figures.
- Compare the result with one independent method or published benchmark.
- Put Transmitter power under a magnifier; the sensitivity table above is the reason why.
- Verify each input against its original source document, not memory.
- Re-run the calculation with a ±10 % stress on the two most sensitive inputs.
- Repeat the ±10 % test on the inputs that matter and see whether the decision — not just the number — still holds.
A routine for decision-grade Antenna Gain
The tool does the arithmetic; the routine below is what makes the arithmetic trustworthy. Five steps, a minute total — and afterwards you will know not just what the number is, but which assumption produced it.
Step 1 — one document, one pass. Open the statement, label or record that holds transmitter power (dbm), antenna gain (dbi), cable + connector loss (db), beamwidth (degrees) 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. If the answer changes your behaviour, it deserves a second run with different assumptions.
Step 2 — start from the case you can defend. Enter pessimistic-but-honest figures first; the optimistic run is a ceiling, not a plan. A conclusion that holds on conservative inputs holds everywhere. Estimates improve most when the worst case is written down in ink.
Step 3 — isolate your variables. Change one field, observe, revert. The live sensitivity list does the ranking for the default inputs; verify it against your own, because dominance shifts when the starting point shifts. Comparisons are cheap: run the identical calculation for the alternative and look at the gap.
Step 4 — stress before you commit. A decision that survives a ten-percent squeeze on its two biggest inputs needs no luck to be sound. One that does not survive is a decision about hope, not about arithmetic. One decimal place more than your data supports is one decimal place of fiction.
Step 5 — schedule the next run. In Technology & Computing the inputs drift quietly. Put a reminder a quarter out, re-enter the same fields, and read the change rather than the level. One decimal place more than your data supports is one decimal place of fiction.
Where Antenna Gain matters in practice
Most Networks & Storage disagreements are arithmetic disagreements in disguise. When Effective radiated power of 46.5 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. The input you reach for first is usually the one you measured longest ago.
The audience for this page is people who need one trustworthy number before their next decision. In professional Networks & Storage practice the pattern is always the same — screen with Antenna Gain, then invest slow analysis only in whatever survives the screen. The input you reach for first is usually the one you measured longest ago.
Nothing here is stored or transmitted, so the habit of checking is free: open the page, re-enter current figures, compare with the number you saved last time. Compare the calculation to the rough guess you arrived with, and ask why they differ.
Quick answers: what searchers ask about Antenna Gain
What affects Antenna Gain the most?
Antenna Gain is driven above all by Transmitter power. Perturbing only that field by ten percent either way produced 49.5 dBm against the 46.5 dBm baseline — a ≈6.5 % response, while Antenna gain manages ≈3.9 %.
Which matters more: antenna gain or transmitter power?
For Antenna Gain, Transmitter power wins the head-to-head (≈6.5 % against ≈3.9 % per ten-percent change). Knowing which input dominates is the difference between careful work and merely slow work.
What is a typical Antenna Gain?
With the example inputs on this page the result is 46.5 dBm, labelled “Point-to-multipoint strong (check licensing)”. “Typical” varies with situation, which is why every result here ships with its verdict band and its sensitivity list: they turn one figure into a range you can locate yourself inside.
How do I calculate Antenna Gain by hand?
Use the stated model — EIRP = tx − loss + gain; directivity ≈ 41000/(az×el); range factor = 10^(dB/20) — and substitute in the order the tool prints (it starts from After cable: 30.0 − 1.5 = 28.5 dBm at the antenna). On the example inputs the hand route lands on 46.5 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 Antenna Gain if transmitter power changes by 10 %?
The engine was re-run with that field moved by ten percent while everything else stayed fixed: the effective radiated power goes across 43.5 dBm to 49.5 dBm, a swing of roughly 6.5 % around the 46.5 dBm baseline. That ratio is the practical definition of how much this input matters.
Is the Antenna Gain result of 46.5 dBm good or bad?
The tool answers “what”, not “whether”: 46.5 dBm carries the verdict “Point-to-multipoint strong (check licensing)” 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.
How often should I check Antenna Gain?
Whenever an input changes by more than a few percent, and otherwise on the rhythm of your decisions — before a purchase, a review, a renewal. Antenna Gain is a snapshot, not a subscription; stale snapshots are the most common silent error in Technology & Computing planning.
How do I calculate Antenna Gain manually?
Write down the inputs, then follow the printed steps in order — EIRP = tx − loss + gain; directivity ≈ 41000/(az×el); range factor = 10^(dB/20). A spreadsheet replicates it with two or three cells. The manual route is worth doing once to build intuition; after that the calculator saves time and eliminates transcription slips.
Does higher gain always help?
Only along the beam axis; the null directions get worse. For coverage of a wide area, gain hurts.
What about dBd vs dBi?
dBd is 2.15 points lower than dBi for the same antenna — mixing the two is the most classic link-budget blunder.
Can this tool see the numbers I type?
It cannot. There is no submission step: the calculation happens in your browser and the result disappears when you close the page. Treat the fields above as a scratchpad rather than a form.
Key terms on this page
- EIRP in milliwatts
- 44,668.4 mW for the Antenna Gain worked case; it sits next to the main result because it carries context the headline leaves out.
- Assumed symmetric beam directivity
- 8.9 dBi in the default Antenna Gain calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Range factor vs isotropic
- 6.68 × in the default Antenna Gain calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Effective radiated power
- The primary output of this tool: 46.5 dBm for the default inputs, computed exactly from EIRP = tx − loss + gain; directivity ≈ 41000/(az×el); range factor = 10^(dB/20).
- Worked example
- Every substitution in order, from the example inputs to 46.5 dBm — the audit trail for the headline figure.
- Verdict band
- The plain-language label — here “Point-to-multipoint strong (check licensing)” — mapping the computed figure onto experience-based ranges for Technology & Computing.
- Sensitivity (±10 %)
- How far the Antenna Gain moves when a single input is nudged ten percent either way; the ranked list on this page is computed live from this engine.
Where the Antenna Gain model comes from
The model is published arithmetic implemented exactly as written: EIRP = tx − loss + gain; directivity ≈ 41000/(az×el); range factor = 10^(dB/20). Source of record: IEEE antenna theory 41000/(az×el) directivity approximation; EIRP = Pt−Lr+Gt definition. Where a professional version of this calculation differs, it differs in inputs and jurisdiction-specific coefficients, not in the algebra — which is why re-checking your inputs beats hunting for a second calculator.
Treat the output as a precise answer to the question you typed: exact arithmetic, transparent formula, published source, no hidden rounding. The design constraint was set by usefulness rather than by comfort: an estimate you can interrogate beats an answer you have to trust.
Turning this Antenna Gain into a decision
Save the number together with its inputs and today’s date; an Antenna Gain figure without context is unusable the moment an input changes.
The audience here is people who need one trustworthy number before their next decision. Everything you need to defend the result — formula, substitution, sensitivity, source — is printed above, so the only remaining variable is the honesty of your inputs.