Home Brew Alcohol Calculator
Your gravity reading before fermentation — write it down on brew day!
Your gravity reading once fermentation has finished bubbling.
A standard homebrew batch is usually 19-23L.
Use 375 for a stubbie/can, 750 for a longneck.
Estimated ABV
4.9%
Standard drinks per 375mL bottle
1.4
Bottles from this batch
53
Dropping from 1.045 to 1.008 gravity gives an estimated 4.9% ABV. A 20L batch fills about 53 bottles of 375mL, and the whole batch adds up to roughly 76.6 standard drinks in total.
Quick answer
A home brew alcohol calculator turns two hydrometer readings into your batch's ABV using (original gravity − final gravity) × 131.25, then works out standard drinks per bottle and total bottles. A 20L batch dropping from 1.045 to 1.008 comes out at about 4.9% ABV, filling roughly 53 stubbies.
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Home Brew Alcohol Calculator is one of brewing and alcohol making tools on OneCalculate — see the full set for this category.
Browse BrewingHow it works
This home brew alcohol calculator only needs three things most brewers already have on hand: two hydrometer readings and a bottle size. Original gravity (OG) is the density of your wort or must before fermentation, when it’s loaded with unfermented sugar. Final gravity (FG) is the same reading once fermentation has stopped bubbling. The bigger the drop between the two, the more sugar converted to alcohol.
The ABV formula behind this home brewing alcohol calculator is the standard, widely-used homebrew approximation:
ABV % = (Original Gravity − Final Gravity) × 131.25So a batch that starts at 1.045 and finishes at 1.008 has dropped 0.037 gravity points, giving 0.037 × 131.25 = 4.9% ABV. It’s the same simple formula most brewers already reach for, and it’s accurate for typical gravities up to roughly 1.070 OG.
Once ABV is known, this homebrew alcohol calculator answers a question plain ABV can’t: how many standard drinks does the whole batch actually pour? It uses Australia’s official definition of a standard drink — 10 grams of pure alcohol, based on an ethanol density of 0.789 g/mL — as set out by the Australian Government Department of Health’s standard drinks guide:
Standard drinks = (Volume mL × ABV % ÷ 100 × 0.789) ÷ 10Applying that to your bottle size gives standard drinks per bottle, and applying it to the whole batch (batch size in litres × 1,000mL) gives a total for everything you’ve brewed. Bottle count is simpler still: batch volume in millilitres divided by bottle size in millilitres. This alcohol calculator for homebrew batches runs all three steps together so you get ABV, drinks per bottle and total bottles from one set of readings.
Worked example
Priya, a home brewer in Adelaide, South Australia, kicks off a 20L batch of pale ale with an original gravity reading of 1.045. Two weeks later, once airlock activity has stopped, she takes a final gravity reading of 1.008. Running the formula: (1.045 − 1.008) × 131.25 = 0.037 × 131.25 = 4.9% ABV, a solid session-strength beer.
Priya usually bottles into 375mL stubbies, but this batch she’s splitting between stubbies for the fridge and 750mL longnecks for gifting. Using the standard drinks formula on each bottle size shows how much that choice matters:
| Bottle size | Bottles from batch | Standard drinks per bottle |
|---|---|---|
| 375 mL stubbie | 53 | 1.4 |
| 750 mL longneck | 27 | 2.9 |
Across the whole 20L batch, that 4.9% ABV works out to roughly 76 standard drinks total — useful for Priya to know before she starts handing bottles out at her next barbecue.
Frequently asked questions
What is a home brew alcohol calculator and how does it work?
It's a tool that turns two hydrometer readings into your batch's alcohol strength. You enter the original gravity (before fermentation) and final gravity (after), and it applies (OG − FG) × 131.25 to estimate ABV, then converts that into standard drinks and bottle counts.
How many standard drinks are in a home brew batch?
It depends on your ABV, batch size and bottle size — there's no single fixed answer. This home brewing alcohol calculator multiplies your batch volume by the ABV and Australia's 0.789 g/mL ethanol density, then divides by the 10g standard drink definition to give a total for the whole batch.
What's a normal OG and FG for a home brew batch?
Most beers start around 1.040–1.055 OG and finish near 1.006–1.012 FG, giving roughly 4–6% ABV. Ciders often start a touch lower, while high-gravity ales and some wines can start well above 1.070, pushing final ABV noticeably higher once fermentation finishes.
How many bottles will my batch fill?
Divide your batch volume in millilitres by your bottle size in millilitres — that's the whole calculation. A 20L (20,000mL) batch bottled into standard 375mL stubbies fills roughly 53 bottles, while the same batch poured into 750mL longnecks fills about 27 instead.
Is a homebrew alcohol calculator accurate without a hydrometer?
Not really — a hydrometer (or a corrected refractometer) is the only practical way to measure the sugar drop that drives this calculation. Without gravity readings before and after fermentation, there's no reliable input for the ABV formula to work from.
Does bottle size change how many standard drinks I get per bottle?
Yes. A larger bottle at the same ABV always contains more standard drinks, since standard drinks scale directly with volume. A 750mL longneck holds roughly double the standard drinks of a 375mL stubbie poured from the exact same batch of beer, cider or wine.
Why does an alcohol calculator for homebrew batches ask for bottle size?
Because ABV alone doesn't tell you how much alcohol is in what you're actually drinking. Pairing ABV with your chosen bottle size lets this calculator report standard drinks per bottle, which is what matters for pacing a session or labelling gifted bottles.
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Written and verified by Nirbhay Tripathi
Last updated 18 August 2026
All rates on this page are verified againstAustralian Government Department of Health — Standard drinks guideon 18 August 2026. See our methodology for the full update calendar.