Three sums, sourced
Every other abv calculator multiplies the gravity you lost by 131.25 and hands you a number.
Free for 14 days. No card needed.
£3 a month
For the person who brews at home and takes a gravity reading before and after, and for the very small brewer doing the same sums on bigger vessels.
Not for someone shopping for kit, malt or hops, not for anyone distilling, and not for a reader who just wants to know what to drink.
Strength
The alcoholic products technical guide multiplies the degrees a beer attenuated by a factor from the Laboratory of the Government Chemist's table, because the yield of alcohol is not constant across strengths. On a 37-degree drop the two methods differ by 0.06%.
Carbonation
Most priming calculators hide an unattributed polynomial. This one starts from the Henry's law constants NIST publishes for carbon dioxide in water, at the temperature your beer actually finished at, and prints the residual it worked from.
Water
Grain absorption, boil-off and the heat your tun steals are different on every setup, so they are inputs rather than assumptions. Measure them once and the strike temperature stops being a guess.
If you want recipe design, a hop and malt database, water chemistry and a mobile brew-day timer in one place, buy a full brewing suite: they are good and they are cheap. Mashzo is for the brewer who wants the three sums done right, with the constant named, and the readings kept.
| Mashzo | A full brewing suite | |
|---|---|---|
| Where the ABV method comes from | HMRC's factor table, printed on the page with the band you picked | Usually the 131.25 shortcut, unattributed |
| Where the priming figures come from | NIST Henry's law constants for CO2 in water, and the residual is shown | A residual-CO2 curve, source rarely stated |
| What it does with your kit's own numbers | Absorption, boil-off and efficiency are inputs you measure once | Equipment profiles, often with vendor defaults |
| What you have to do before you get an answer | Nothing: the calculators are open and free | Usually an account, sometimes a trial clock |
Prices and features of other brewing software change; nothing on this row names a competitor's price, because we do not publish figures we have not measured and dated ourselves.
Tools
HMRC does not, and neither does this one: the alcoholic products technical guide says to multiply the degrees a beer attenuated by a factor from a table the Laboratory of the Government Chemist produced, because the yield of alcohol is not the same at every strength.
A beer that fell from 1.048 to 1.011 dropped 37 degrees; the factor for that line is 0.130, and the answer is 4.8%: the shortcut says 4.86%. Three free calculators here work the three sums a brew day makes you do, and each one prints the constant it used and where it came from.
Free to use. No account, no card, no sign-up.
In figures
18.58GBP
Median published figure, the middle half 12.43 to 57.27 GBP
4 sources with a published figure, read 18 October 2026.
Mashzo Pro
£3
per month, whole team
Pro keeps your recipes and your readings, so the efficiency and boil-off you measured last time are already in the boxes next time.
Free for 14 days. No card needed.
£3 a month Billed monthly. Cancel any time from your account page. Price and renewal terms are shown before checkout.