Attenuation Calculator
The formula
What the attenuation tells you
The hydrometer maths behind attenuation: ABV, apparent attenuation and points consumed from two gravity readings.
Calculation: ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100. Enter your inputs and every substitution is shown below the result.
Reading the result
90 %+ attenuation reads dry; under 70 % is sweet or stuck — the attenuation band diagnoses as much as the ABV.
Limitations and best practice
The 131.25 factor loses a few tenths above 8 % ABV where alcohol density effects grow.
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 an estimate?
Can I read FG too early?
Source & methodology
Standard brewing arithmetic (De Clerck).
Attenuation: what this tool answers
This page was written for one job: turning your own inputs into a defensible figure, with the working shown. Attenuation is the kind of number people argue about from memory. This page ends that argument with arithmetic you can watch happen: enter your figures, get Estimated ABV in real time, and see every substitution printed below.
A calculation like this one is worth roughly as much as a careful sentence: it forces several vague considerations into one comparable quantity. Once Attenuation is on the table, the argument can stop being about impressions.
In Science & Research the same quantity is often quoted under two or three different conventions. The formula printed above fixes one convention and applies it consistently, which is what makes results from this page comparable with each other.
What makes a calculation page trustworthy is that its copy is derived from its own arithmetic: here estimated ABV = 4.99 %, recomputed every time a field changes, and the sensitivity section ranks the inputs that move the result — Original gravity first, at ≈275.8 % of the headline for a ten-percent overstatement of that input. Work down the page and by the end you could re-derive the result in a spreadsheet from memory.
The Attenuation formula, explained
Here is the complete model this tool runs — ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100 — with each input explained below. If a competitor’s page gives you a different answer from the same inputs, this is the text that settles which of you is right.
Original gravity (example value 1) is a measured number in the unit named by the label; the formula does not convert for you. The example value is there to demonstrate the mechanics, not to describe your situation — overwrite it.
Final gravity (example value 1) 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.
The default Attenuation calculation, written out in full
Abstract formulas are hard to trust, so here is the complete substitution using the default inputs, written the way an examiner would want it. Starting figures: Original gravity, Final gravity. The endpoint of that chain is 4.99 % of estimated ABV, sitting in the “Standard table beer range” band.
- Δ gravity = 1.048 − 1.010 = 0.038
- ABV = × 131.25 = 4.99 %
- Attenuation = Δ ÷ OG-points = 79.2 %
Attenuation — 79.2%. Read next to the headline, this is the figure that shows the shape of the trade-off.
Points consumed — 38.0 pts. If your inputs change, this is usually the first companion figure to move.
Real extract left (approx) — 10.0 °P. Read next to the headline, this is the figure that shows the shape of the trade-off.
Overwrite any input above and every line of this example updates with it — the substitution is live, not a screenshot of somebody else’s numbers.
The Attenuation 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? Settings beyond this model’s valid range were dropped rather than guessed at, which is why the table is shorter on one side.
| Original gravity setting | Estimated ABV |
|---|---|
| example inputs | 4.99 % |
| 110 % of the example value | 18.74 % |
| 120 % of the example value | 32.50 % |
The corridor runs from 4.99 % to 32.50 % across that band — which is the range worth planning inside rather than the single 4.99 % point estimate. Reproduce it in the form above by editing Original gravity alone; the substitution steps will follow your figures exactly.
The levers behind Attenuation, ranked by effect
Each numeric input was probed by ten percent and the estimated ABV recomputed from scratch with every other field frozen; where a model has a boundary — a ratio that cannot fall below 1, a count that cannot go negative — only the probe that stays inside the boundary is listed. Read it as a map of where Attenuation is fragile — drawn for the example inputs, which is the map you want when deciding what to measure carefully.
- Original gravity +10 % → 18.74 % against 4.99 % at the example inputs (≈275.8 %); the opposite direction leaves the model’s valid range, so it was not computed
- Final gravity −10 % → 18.24 % against 4.99 % at the example inputs (≈265.8 %); the opposite direction leaves the model’s valid range, so it was not computed
Original gravity is the dominant lever here: a ten-percent increase moves the result by about 275.8 %, from 4.99 % at the example value up to 18.74 %. Measure that input from a document rather than from memory, and Final gravity is effectively tied with it (≈265.8 % for the same nudge), so verify the pair together. The rest of the inputs earn only a rounding-error of attention, and that asymmetry is the practical payoff of measuring rather than asserting.
Interpreting the Attenuation verdict
Nobody acts on a bare figure — they act on a figure with a comparison attached. On the example inputs the band reads “Standard table beer range”; your own figures place you on a different rung of the same ladder. Before treating the band as fact, note its width: a ten-percent increase on Original gravity already spans 4.99 % at the example value up to 18.74 % — the opposite direction leaves this model’s valid range, so only the upper probe is reported. The practical reading rules: read the band as a starting hypothesis, then test it: change the two dominant inputs by ten percent and see whether the verdict survives. Verdicts that survive stress are the ones worth acting on.
In Science & Research, Attenuation is one instrument in an orchestra: on its own it is a number, next to Attenuation and Points consumed it becomes a diagnosis. The tools linked above exist so the headline never has to carry that weight alone.
The errors that quietly break an Attenuation figure
The 131.25 factor loses a few tenths above 8 % ABV where alcohol density effects grow. 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 Attenuation 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.
This model has its own particular trap: Original gravity carries ≈275.8 % of the response per ten percent of error, so effort spent elsewhere is largely decorative.
A final trap is presentation: reporting Attenuation 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.
Attenuation verification checklist
- Record the date and the inputs alongside the number so future-you knows what was assumed.
- Compare the output against one published benchmark or a colleague’s independent estimate.
- Check Original gravity before anything else: it is the measured dominant input, ≈275.8 % of Attenuation per ten percent.
- Re-run the calculation with a ±10 % stress on the two most sensitive inputs.
- State, in one sentence, which convention each rate, unit or period in the form is using.
- Repeat the ±10 % test on the inputs that matter and see whether the decision — not just the number — still holds.
Five steps from raw inputs to a figure you can defend
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 — gather before you type. Attenuation depends on original gravity, final gravity. Collect them from a source document — a statement, a report, an invoice, a log — rather than from memory, because recalled inputs are the single largest cause of wrong results. Most surprises in numbers are surprises about inputs, not about formulas.
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. 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. The inputs are the part of the work that nobody else can do for you.
Step 4 — compute a corridor, not a point. Three runs — worst, likely, best — turn Attenuation from a snapshot into a range. Plan against the pessimistic end and treat the optimistic end as the upside story. Write the figure down before moving on; memory flatters whichever number you saw last.
Step 5 — schedule the next run. In Science & Research the inputs drift quietly. Put a reminder a quarter out, re-enter the same fields, and read the change rather than the level. Repeating a calculation with the same numbers proves only that the arithmetic is reliable — which is worth knowing.
The real-world conversations Attenuation settles
In Physics Laboratory the figure computed here is usually the first one somebody asks to see. Having it — with the formula behind it — changes your position in the conversation from participant to reference. Half of a good calculation is knowing which input you would hate to be wrong about.
The companion outputs — Attenuation and Points consumed — exist for the second stage of that screen: the headline sizes the prize, while the companions describe the trade-off you are accepting to get it. Repeating a calculation with the same numbers proves only that the arithmetic is reliable — which is worth knowing.
Treat Attenuation like a smoke alarm rather than a painting — its value is in being tested periodically, not in being admired once. Compare the calculation to the rough guess you arrived with, and ask why they differ.
Quick answers: what searchers ask about Attenuation
What affects Attenuation the most?
The short answer: Original gravity. The longer answer is the sensitivity table on this page, where every numeric input was probed by ten percent and the estimated ABV recalculated — Original gravity moved it furthest, by roughly 275.8 % (4.99 % at the example value up to 18.74 %).
Do final gravity and original gravity matter equally?
On these inputs, yes: the two measured within a rounding error of each other — ≈275.8 % and ≈265.8 % of the estimated ABV per ten-percent change. Treat them as one pair to verify together rather than ranking them.
What is a typical Attenuation?
With the example inputs on this page the result is 4.99 %, labelled “Standard table beer range”. “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 Attenuation by hand?
ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100 is the entire method. Work the inputs in that order — Δ gravity = 1.048 − 1.010 = 0.038 — and you will reach 4.99 % on the default figures, the same number this tool prints.
What happens to Attenuation if original gravity changes by 10 %?
On these inputs a +10 % change in original gravity takes Attenuation to 18.74 % against the 4.99 % example — around 275.8 % of the headline. The same test on every other field is in the sensitivity section.
Is the Attenuation result of 4.99 % good or bad?
The tool answers “what”, not “whether”: 4.99 % carries the verdict “Standard table beer range” 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.
Is Attenuation accurate?
The arithmetic is exact: ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100 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 4.99 % result as the correct answer to the question you typed — and check the assumptions section before acting on it.
How many significant figures are reliable in Attenuation?
About as many as your least precise input. The tool computes at full precision and displays rounded output; report 4.99 % to a decimal place your inputs can actually support.
Why an estimate?
Distillation-free lab methods (density + refractive) exist; the (OG−FG)×131.25 is the accepted homebrew standard with <0.3 % typical error.
Can I read FG too early?
Confirm terminal gravity over three days before calling it; attenuation hides in stalled ferments.
Is my data private on this page?
Yes — computation happens locally in your browser, with no account, no tracking of your inputs and nothing sent to a server. The printed formula is the whole story of what happens to your figures.
Key terms on this page
- Attenuation
- 79.2% for the Attenuation worked case; it sits next to the main result because it carries context the headline leaves out.
- Points consumed
- 38.0 pts for the Attenuation worked case; it sits next to the main result because it carries context the headline leaves out.
- Real extract left (approx)
- 10.0 °P for the Attenuation worked case; it sits next to the main result because it carries context the headline leaves out.
- Estimated ABV
- The primary output of this tool: 4.99 % for the default inputs, computed exactly from ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100.
- Worked example
- Every substitution in order, from the example inputs to 4.99 % — the audit trail for the headline figure.
- Verdict band
- A named zone on the range of plausible results; the example inputs land in “Standard table beer range”, and your inputs may not.
- Sensitivity (+10 %)
- How far the Attenuation moves when a single input is nudged ten percent, in whichever direction the model accepts; the ranked list on this page is computed live from this engine.
Method, sources and what this tool cannot tell you
The model is published arithmetic implemented exactly as written: ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100. Source of record: Standard brewing arithmetic (De Clerck). Specialist software layers extra coefficients on top of the same algebra; none are hidden here, and that transparency is what makes a disagreement traceable to a specific input instead of a black box.
Nothing here replaces a qualified professional, and nothing here is approximate either — the arithmetic is exact, and the honesty is in the inputs you supply. What that buys you is reproducibility — two people, two browsers, the same arithmetic, and a printed trail from inputs to result that either of them can audit.
Turning this Attenuation into a decision
Re-run the calculation with your own figures, stress the two most sensitive inputs by ±10 %, and only then act on the result.
Whoever you are (people who need one trustworthy number before their next decision), the next step is the same: replace the example inputs with your own, note the date, and re-run whenever a figure moves. In Science & Research, a dated figure is a trend, and an undated one is a rumour.