Final Gravity Calculator
The formula
What the final gravity tells you
The hydrometer maths behind final gravity: 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).
Final Gravity: the number, the method and the caveats
You are here because you need a specific number, and you want to see how it was produced before you rely on it. Final Gravity 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.
People rarely disagree about arithmetic; they disagree about assumptions that were never written down. Printing the substitution and the sensitivity ranking removes that category of disagreement for Final Gravity.
The useful way to hold Final Gravity is as a ratio with a story attached: ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100 says how the parts combine, and the 4.99 % figure above is simply that sentence written in numbers. Everything that follows unpacks one clause of the sentence at a time.
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.
Inside the Final Gravity calculation: formula and every input
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 plain measured quantity — the unit shown in the label is the unit the formula expects. This input feeds the formula directly; a defensible figure here is worth more than false precision anywhere else.
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.
Final Gravity with real numbers, step by step
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%. If your inputs change, this is usually the first companion figure to move.
Points consumed — 38.0 pts. This is the number experienced users quote when the headline alone would mislead.
Real extract left (approx) — 10.0 °P. This is the number experienced users quote when the headline alone would mislead.
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.
Scenario table: Final Gravity at ±10 % and ±20 % of the key input
The honest version of any estimate is a corridor, and this one is cheap to produce: Final Gravity was recomputed at 3 points along the dominant input, with every other field left untouched. 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 % |
That spread — 4.99 % at the low end, 32.50 % at the high — is what a careful read of Final Gravity looks like: a band you can state out loud, with the reason for each edge. Reproduce it in the form above by editing Original gravity alone; the substitution steps will follow your figures exactly.
Where Final Gravity is fragile — and where it is not
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. It is the fastest honest answer to “what matters most in Final Gravity?” — and it is specific to these defaults, because sensitivity moves with the starting point.
- Only one side of Original gravity can be probed here — +10 % gives 18.74 % versus 4.99 %, a ≈275.8 % response on the estimated ABV
- 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 %. 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. Everything below that can stay approximate, which is a licence to stop chasing data that would not change the decision.
Is your Final Gravity good — reading the result bands
The value above only becomes useful the moment you know what it is being measured against. The default case lands in the “Standard table beer range” band, and bands are deliberately wide because real situations overlap. How much of that band is luck? On Original gravity alone a ten-percent increase covers 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.
Set Final Gravity beside its neighbours and it usually plays a specific role: this figure establishes the size of something, and the neighbouring tools establish whether that size is acceptable. Skipping the first step makes the second one arbitrary.
How people get Final Gravity wrong
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.
Treating the example inputs as a recommendation. They are a demonstration of the mechanism — a decision-grade Final Gravity begins the moment your own figures replace them.
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.
The subtlest error is answering the wrong question precisely. Confirm that estimated ABV is actually the quantity your decision needs — the arithmetic is flawless either way, which is what makes the mistake invisible.
Six things to confirm before acting on Final Gravity
- Note the date and the inputs beside the number so the figure can be audited later.
- Verify each input against its original source document, not memory.
- Check Original gravity before anything else: it is the measured dominant input, ≈275.8 % of Final Gravity per ten percent.
- 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.
- Confirm the answer against one independent method or published benchmark for Final Gravity.
A routine for decision-grade Final Gravity
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 Final Gravity takes a minute to learn and applies to every input above.
Step 1 — collect, then type. Everything this tool asks for is listed above (original gravity, final gravity). Pull each figure from something you can point at — paperwork, a dashboard, a label — before touching a field. Guesswork at the input stage cannot be repaired at the interpretation stage. The inputs are the part of the work that nobody else can do for you.
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. The test of a good estimate is not that it feels right but that it changes what you do.
Step 3 — change one input at a time. Nudge a single field by ten percent, watch the headline and its companions move, then undo it. Two or three fields will dominate — the sensitivity table above already ranks them for this engine. Re-running a number costs seconds; retracting a decision costs considerably more.
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. If the answer changes your behaviour, it deserves a second run with different assumptions.
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. The inputs are the part of the work that nobody else can do for you.
The real-world conversations Final Gravity settles
In Fermentation 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. The fastest sanity test is to guess the answer first and see how far the calculation disagrees.
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. Suspiciously tidy answers deserve the same scrutiny as untidy ones.
There is a personal-administration use people overlook: periodic self-checking. Final Gravity 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. If the answer changes your behaviour, it deserves a second run with different assumptions.
The questions that come up most about Final Gravity
What affects Final Gravity 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?
Final Gravity here is co-driven: Original gravity and Final gravity produced ≈275.8 % and ≈265.8 % responses, which is a tie for practical purposes. Everything below those two is a rounding error by comparison.
What is a typical Final Gravity?
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 Final Gravity by hand?
Three steps: write the formula (ABV ≈ (OG − FG) × 131.25; attenuation = (OG−FG) ÷ (OG−1) × 100), insert your values, and simplify. The worked example section shows exactly that chain for the default inputs; replicating it once on paper teaches you more about Final Gravity than any number of calculator runs.
What happens to Final Gravity if original gravity changes by 10 %?
Try it in the form above and the printed substitution will follow you; the pre-computed answer for the defaults is 4.99 % at the example value up to 18.74 % across the ten-percent probe — the opposite direction leaves this model’s valid range, so only the upper probe is reported, i.e. ≈275.8 % sensitivity on the estimated ABV.
Is the Final Gravity 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.
Can Final Gravity be negative or empty?
Yes, and that is informative rather than broken: a negative Final Gravity usually means the inputs encode an outflow or a shortfall, and the verdict band above labels exactly that situation instead of hiding it.
What affects Final Gravity the most?
Sensitivity depends on where you start, but the inputs Original gravity and Final gravity typically move Final Gravity further than the rest because they enter the formula multiplicatively. If you can only measure two things well, measure those and hold the others at conservative defaults.
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.
Glossary for Final Gravity
- Attenuation
- 79.2% on the example inputs — a companion figure printed beside the headline of Final Gravity so that no result is read in isolation.
- Points consumed
- 38.0 pts in the default Final Gravity calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Real extract left (approx)
- 10.0 °P in the default Final Gravity 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
- Every substitution in order, from the example inputs to 4.99 % — the audit trail for the headline figure.
- 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 Final Gravity 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 Final Gravity calculation
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). 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.
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. The design constraint was set by usefulness rather than by comfort: an estimate you can interrogate beats an answer you have to trust.
Next steps after the calculation
Re-run the calculation with your own figures, stress the two most sensitive inputs by ±10 %, and only then act on the result.
This page was written for people who need one trustworthy number before their next decision, and the promise is that nothing above required trust. Bookmark the tool, re-run it whenever an input moves by more than a few percent, and keep the date with the number.