Real Attenuation Calculator
The formula
What the real attenuation tells you
The hydrometer maths behind real 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).
Real Attenuation: what this tool answers
You are here because you need a specific number, and you want to see how it was produced before you rely on it. Searchers land on a Real Attenuation 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 number itself is the easy part. What takes judgement is knowing which inputs are facts in your situation and which are guesses wearing a decimal point — a distinction this page makes explicit for every field above.
It helps to separate the mechanics from the interpretation. The mechanics are fixed: ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100. Anyone, anywhere, entering the same inputs will get the same 4.99 %. The interpretation is where experience counts: whether 4.99 % is good, normal or alarming depends on comparisons covered below, and that is the part most articles about Real Attenuation never explain.
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. Read the sections in order and you will be able to reproduce every figure by hand.
The Real Attenuation formula, explained
One formula, published in full: ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100. 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.
Original gravity (example value 1) is a measured number in the unit named by the label; the formula does not convert for you. Replace the example with the figure from your own records — the tool recomputes instantly and the printed steps follow your numbers.
Final gravity (example value 1) is a quantity rather than a category — precision here is cheap and worth having. Replace the example with the figure from your own records — the tool recomputes instantly and the printed steps follow your numbers.
Real Attenuation on the example inputs: the complete substitution
Rather than describe the calculation, here it is end to end — every substitution in order, starting from the inputs above. Starting figures: Original gravity, Final gravity. Run to the end, the estimated ABV resolves to 4.99 % — Standard table beer range on the bands this tool uses.
- Δ gravity = 1.048 − 1.010 = 0.038
- ABV = × 131.25 = 4.99 %
- Attenuation = Δ ÷ OG-points = 79.2 %
Attenuation — 79.2%. This is the number experienced users quote when the headline alone would mislead.
Points consumed — 38.0 pts. Compare it against the main result of 4.99 % before drawing conclusions.
Real extract left (approx) — 10.0 °P. This is the number experienced users quote when the headline alone would mislead.
Keep this worked example open while you enter your own figures: matching the shape of the substitution is the fastest way to spot a unit or convention mistake.
How far Real Attenuation can reasonably move
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 Real Attenuation, ranked by effect
This list was computed for this engine just now: ten percent on one input at a time, everything else on its example value. Some fields can only be tested in one direction here, and those rows say so instead of inventing a second figure. It is the fastest honest answer to “what matters most in Real Attenuation?” — and it is specific to these defaults, because sensitivity moves with the starting point.
- 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
- Only one side of Final gravity can be probed here — −10 % gives 18.24 % versus 4.99 %, a ≈265.8 % response on the estimated ABV
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 %. That is where a careless figure does the most damage, so check it against a source, and Final gravity is effectively tied with it (≈265.8 % for the same nudge), so verify the pair together. 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.
What a Real Attenuation of 4.99 % means in practice
Nobody acts on a bare figure — they act on a figure with a comparison attached. The verdict attached to the default calculation — “Standard table beer range” — is one band on a ladder your own figure may sit somewhere else on. 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: 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.
In Cooking & Food Science, Real 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.
Why Real Attenuation results go wrong — and how to prevent it
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.
Copying a single headline number without checking the companion outputs. The tool reports Attenuation, Points consumed and Real extract left (approx) alongside the main result precisely because Real Attenuation in isolation misleads — the secondary columns are where outliers and trade-offs show up.
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.
Another is comparing across contexts: a Real Attenuation 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.
Six things to confirm before acting on Real Attenuation
- Check that every field the formula needs actually arrived from a document, not from recollection.
- Confirm the example values are plausible for your own situation before replacing them.
- Check Original gravity before anything else: it is the measured dominant input, ≈275.8 % of Real Attenuation per ten percent.
- Verify each input against its original source document, not memory.
- Compare the output against one published benchmark or a colleague’s independent estimate.
- Confirm the answer against one independent method or published benchmark for Real Attenuation.
Step by step: getting a trustworthy Real Attenuation out of this tool
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 original gravity, final gravity 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 — 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. A result worth acting on survives having its two shakiest inputs halved.
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. Repeating a calculation with the same numbers proves only that the arithmetic is reliable — which is worth knowing.
Step 4 — ask what would have to be true. Take the result you want and work backwards through the inputs until you find the assumption that produces it; then decide honestly whether that assumption is defensible. The test of a good estimate is not that it feels right but that it changes what you do.
Step 5 — save the story with the figure. A number without its inputs and its date is unusable within a quarter. Record 4.99 %, the assumptions behind it, and today’s date; your future self will be auditing a stranger’s arithmetic. A result worth acting on survives having its two shakiest inputs halved.
The real-world conversations Real Attenuation settles
Numbers earn their keep in conversations, and Real Attenuation is no exception. In Cooking & Food Science discussions around Fermentation, this figure decides whether an option stays on the table: it converts an opinionated debate into an arithmetic one, and arithmetic is the only referee both sides accept. Repeating a calculation with the same numbers proves only that the arithmetic is reliable — which is worth knowing.
Used properly this is a five-minute filter that saves weeks. Compute Real Attenuation, reject what fails, and only then bring in the expensive analysis for the survivors. When two sources disagree, it is almost never the arithmetic that differs.
There is a personal-administration use people overlook: periodic self-checking. Real Attenuation quietly drifts as life changes — rates move, bodies change, costs compound — and re-running it a few times a year catches drift while correction is still cheap. One decimal place more than your data supports is one decimal place of fiction.
Real Attenuation — frequently asked questions
What affects Real Attenuation the most?
Measured on this engine, Original gravity is the dominant lever: moving it +10 % shifts the estimated ABV across 4.99 % at the example value up to 18.74 % — about 275.8 % of the headline, with Final gravity next at ≈265.8 % — the opposite direction leaves this model’s valid range, so only the upper probe is reported. The ranked list in the sensitivity section is computed live, not asserted from a template.
Do final gravity and original gravity matter equally?
Effectively. Measured on this engine they land at ≈275.8 % and ≈265.8 % for the same ten-percent nudge, so the honest advice is to get both right; chasing precision in only one of them buys almost nothing.
What is a typical Real 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 Real 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 Real Attenuation if original gravity changes by 10 %?
On these inputs a +10 % change in original gravity takes Real 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 Real Attenuation result of 4.99 % good or bad?
Good and bad are comparisons, so the honest test is three questions: where does your own Real Attenuation sit against the 4.99 % reference above, how far would a plausible input error move it (≈275.8 % per ten percent on Original gravity), and what does the alternative option compute to?
Is Real 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.
Can Real Attenuation be negative or empty?
Yes, and that is informative rather than broken: a negative Real Attenuation usually means the inputs encode an outflow or a shortfall, and the verdict band above labels exactly that situation instead of hiding it.
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 Real Attenuation worked case; it sits next to the main result because it carries context the headline leaves out.
- Points consumed
- 38.0 pts on the example inputs — a companion figure printed beside the headline of Real Attenuation so that no result is read in isolation.
- Real extract left (approx)
- 10.0 °P in the default Real Attenuation calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- 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
- The step-by-step substitution printed above, so the arithmetic can be re-derived by hand or in a spreadsheet.
- Verdict band
- The plain-language label — here “Standard table beer range” — mapping the computed figure onto experience-based ranges for Cooking & Food Science.
- Sensitivity (+10 %)
- How far the Real 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.
The provenance of this Real Attenuation calculation
Everything above runs on one stated formula, applied without hidden coefficients: ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100. Source of record: Standard brewing arithmetic (De Clerck). 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.
This page is an estimation aid, not professional advice. The design rule is simple: two people entering identical figures must get identical answers. The sensitivity table above is part of that promise rather than a bonus: it lets you see how much of the result depends on how carefully you measured.
What to do with your Real Attenuation next
Save the number together with its inputs and today’s date; a Real Attenuation 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.