Homebrewing generates more numbers than most hobbies — gravity readings, alcohol percentages, bitterness units, colour values, carbonation volumes, mash ratios — and most of them are connected to each other in ways that aren't obvious until you've traced through the arithmetic once. This guide is that one trace-through: every major number a homebrewer works with, what it actually measures, where it comes from, and which of this site's tools computes it.
Gravity: the number everything else is built on
Nearly every other calculation on this site starts from a gravity reading. Specific gravity is the density of your wort or beer relative to water — dissolved sugar makes a liquid denser than plain water, so wort reads above 1.000 in proportion to how much sugar is dissolved in it. Original gravity (OG) is that reading taken before fermentation starts; final gravity (FG) is the same reading taken once fermentation is done.
The scale most homebrewers use — specific gravity — isn't the only one. Degrees Plato, common in German and Central European brewing, expresses the same dissolved-extract concentration as a percentage by weight rather than a density ratio, and Brix, more common in winemaking and cider, reads within about 0.2° of Plato for wort-strength solutions. See the SG to Plato/Brix conversion chart if you need to move between scales.
Whichever scale you read from, remember that a hydrometer is calibrated to a specific reference temperature — usually 60°F or 68°F — and a reading taken at any other temperature needs correcting. The hydrometer temperature correction chart covers this in detail; it's one of the most common sources of a gravity reading that looks "off" for no obvious reason.
ABV: what OG and FG actually tell you
The ABV / Attenuation Calculator takes your OG and FG and computes alcohol by volume two ways — the simple (OG - FG) x 131.25 formula most homebrewers learn first, and a more accurate advanced formula that tracks better at higher gravities. It also computes apparent attenuation and real attenuation, which are two different (and commonly confused) ways of expressing how much of your wort's fermentable sugar the yeast actually consumed. Real attenuation is always a few points lower than apparent, because dissolved alcohol makes a hydrometer read artificially low — see the apparent vs. real attenuation quick reference for the short version, or the full blog post for the complete explanation.
If your ABV or attenuation is coming out lower than expected, the yeast strain you pitched is usually the first place to look — every strain on the yeast reference states its manufacturer-published attenuation range, and a strain rated for 65-70% will never hit the dry finish a strain rated 78-82% would, no matter how long you leave it in the fermenter.
IBU: two formulas, one honest disagreement
Bitterness works differently from gravity — it isn't measured directly by most homebrewers at all, but estimated from a hop schedule using a published utilization model. The IBU Calculator runs your hop additions (variety, alpha acid, weight, boil time) through both the Tinseth and Rager formulas simultaneously, because the two routinely disagree on an identical schedule — sometimes by 20-30%, sometimes by considerably more on a big, high-gravity beer, and not always in the same direction. Neither is more "correct" — they're different models built on different assumptions, and the Tinseth vs. Rager explainer walks through exactly where and why they diverge.
Every hop's contribution starts with its alpha acid percentage — the hop reference lists the typical published range for dozens of real varieties, from high-alpha bittering hops like Columbus and Warrior to delicate noble aroma hops like Saaz and Hallertau Mittelfrüh. Alpha acid varies by crop year and growing region even within the same named variety, so treat the published range as a planning figure and check the actual Certificate of Analysis for precision.
SRM: colour from a grain bill
The SRM Colour Calculator estimates your beer's colour using the Morey equation, working from each grain's weight and its Lovibond colour rating — the same figures listed on every page in the malt reference. A small amount of very dark specialty malt (chocolate malt, roasted barley, black patent) moves SRM disproportionately more than a large amount of pale base malt, which is both a useful fine-tuning lever and a common cause of a grain bill turning out darker than planned. See the SRM to beer colour name chart for how a computed SRM value maps to the pale-straw-to-black naming convention most style guidelines use.
Water chemistry: the ingredient most recipes ignore
Mash pH, extraction efficiency and perceived balance between hop bitterness and malt sweetness are all shaped by your brewing water's mineral content — calcium, magnesium, sulfate, chloride and bicarbonate. The water profile reference covers classic brewing-city profiles, from Burton-on-Trent's famously sulfate-loaded water (which shaped English pale ale's sharp, dry character) to Pilsen's extremely soft water (which let Pilsner develop as a delicately hopped, pale lager with nothing pushing back against a heavier hop rate). Gypsum and calcium chloride are the two most commonly adjusted salts, pushing perceived balance toward sharper hop character or fuller malt character respectively.
Mash temperature and strike water
Strike water is the first calculation that actually touches the mash, and it's less forgiving of a late correction than anything before it on brew day: once grain and water are combined, there's no easy way to cool a mash that overshot or reheat one that undershot without also risking uneven starch conversion. The Strike Water & Mash Temperature Calculator exists specifically to get that number right before the two ever meet, using John Palmer's published formula rather than a rule-of-thumb ratio guessed from memory. See the mash temperature and body quick reference for how the target temperature itself — not just hitting it accurately — shapes the finished beer's fermentability and body.
Carbonation: the calculation with a real safety dimension
Priming sugar is the one calculation on this site with a genuine safety consequence if it's badly wrong. The Priming Sugar Calculator accounts for the CO2 your beer is already holding at its current temperature, not only the volumes you're targeting — colder beer carries more dissolved CO2 at equilibrium, so a beer that fermented warm needs a larger priming charge than one that fermented cold to land on the same final carbonation. Push a target too high and you risk over-carbonation: most standard bottles are rated safely only to about 3.5-4 volumes of CO2, beyond which the risk of a bottle failing under pressure rises sharply. The CO2 volumes by style chart gives typical carbonation targets by style, and the corn sugar vs. table sugar vs. DME post covers how sugar choice changes the required dose at a fixed CO2 target.
Dilution and blending: adjusting after the fact
Sometimes a batch comes out stronger or weaker than planned, and the fix is arithmetic rather than a redo. The Dilution & Blending Calculator covers the two ways a finished batch's numbers get corrected after the fact: adding water to bring an over-strength batch down to a target gravity, or combining two mismatched batches so their blended gravity lands where you actually wanted it. Both modes work in gravity points — (SG - 1) x 1000 — because gravity points, unlike specific gravity itself, are additive across volumes. See when to dilute vs. when to blend for guidance on which mode actually fits your situation.
Style guidelines: where all these numbers converge
Every number this guide has covered — OG, FG, IBU, SRM, ABV — comes together on the style guideline reference, where dozens of beer, cider and mead styles each state their approximate target range (from the BJCP 2021 Style Guidelines) alongside the real history and character that produced that range. If you're not sure whether your calculated numbers are in a sane place for what you're trying to brew, the relevant style page is the fastest sanity check — and if your cider or mead numbers don't have an IBU or SRM range to check against at all, that's not a gap in this guide; those styles genuinely don't have a conventional range in most references, and the style pages say so honestly rather than inventing one.
Cider and mead: the same arithmetic, different starting material
Cider and mead brewers use nearly the same measurement toolkit as beer brewers — gravity readings, ABV calculation, priming sugar — but a few things genuinely differ. There's no mash, no sparge and no grain bill at all: fermentation starts directly from pressed apple juice (cider) or diluted honey (mead), so the strike water calculator and the malt reference simply don't apply. There's also no conventional IBU or SRM range for either — the style guideline reference lists cider and mead entries honestly without inventing numbers for fields that don't have a widely agreed target.
What does carry over directly: the ABV calculator works identically on cider and mead gravity readings, and the priming sugar calculator applies the same physics to a bottle-conditioned cider as it does to a beer. What changes is the starting gravity range — mead in particular often starts far higher than any beer style, commonly 1.085-1.140 or beyond for a traditional dry mead, simply because honey is a far more concentrated sugar source than malt extract. Yeast choice differs sharply too: wine yeasts like EC-1118, 71B, D47 and K1-V1116 (all covered in the yeast reference) are bred for high-gravity, high-alcohol-tolerance fermentation in a way most beer yeast strains simply aren't suited for, and pitching a beer yeast into a high-gravity mead must is a common beginner mistake that leads to a stalled, incomplete fermentation.
Extract vs. all-grain: what actually changes in the math
Extract brewers skip the mash entirely, starting from a malt extract (liquid or dried) that's already had its starch converted for them at the maltster or extract producer. This doesn't change the ABV, IBU or SRM calculations at all — they work identically off the OG/FG readings, hop schedule and colour contribution regardless of how the wort's sugar got there. What it does remove is the strike water calculation and any need to think about diastatic power, since there's no mash conversion happening on brew day at all. Extract brewers steeping specialty grains (crystal, roasted malts) for colour and flavour without mashing them still use the same SRM calculator and the same malt reference figures for those steeped grains, since colour contribution from a non-diastatic specialty grain works the same steeped as it does mashed.
A common point of confusion: why "attenuation" alone doesn't tell you ABV
It's tempting to think a yeast strain's published attenuation percentage alone should be enough to predict ABV, without needing a separate calculation. It isn't, because attenuation is a percentage of extract converted, and the absolute amount of alcohol that percentage produces still depends entirely on how much extract was there to begin with. A yeast at 75% attenuation on a 1.040 OG wort produces meaningfully less alcohol than the same yeast at the same 75% attenuation on a 1.080 OG wort — which is exactly why the ABV calculator needs both OG and FG as inputs, not attenuation alone. This is also why two brewers can both correctly say "I got 75% attenuation" on very differently strong beers.
Frequently confused pairs, in one place
A few terms get mixed up often enough that it's worth listing them side by side rather than trusting a reader to have absorbed the distinction from a single earlier mention. Apparent vs. real attenuation: apparent comes straight from your two gravity readings; real corrects for dissolved alcohol making a hydrometer read low, and is always the lower of the two numbers for the same OG/FG pair. Simple vs. advanced ABV formula: simple is a fast linear approximation; advanced tracks more accurately at higher gravities, and the two formulas converge closely at normal beer strengths. Tinseth vs. Rager IBU: two independently built utilization models that routinely disagree, with the gap widening (and Rager pulling ahead) on big, high-gravity, heavily late-hopped beers, but capable of running the other way on a mid-boil addition. Plato vs. Brix: numerically near-identical for wort-strength solutions, but Plato is the traditional brewing-science scale while Brix is more common in winemaking and increasingly in cider.
A short glossary, if you'd rather skim than click through
Beyond the terms already linked above, a handful of others come up constantly enough to be worth a one-line definition right here: wort is unfermented sugary liquid before yeast is pitched; trub is the sediment of spent hops and protein material that settles out during and after the boil; krausen is the foamy head that forms during active fermentation; flocculation describes how readily a yeast strain clumps and drops out of suspension once fermentation slows; and diacetyl is a buttery off-flavour byproduct most healthy yeast reabsorb late in fermentation if given time and slightly warmer temperatures.
Where to start
If you're mid-recipe right now, jump straight to whichever calculator answers your immediate question. If you're planning ahead, start with a target style, check its numbers against the style reference, then work backward through grain bill (via malts), hop schedule (via hops) and yeast strain (via yeast) to a recipe that should land where you want it — checking each step against the relevant calculator as you go, rather than trusting the final numbers to work out on their own.
Bookmark whichever calculator page you end up using most on brew day — every tool reads its inputs back out of its own URL, so a bookmarked link with your usual batch size and water:grain ratio already filled in saves re-typing the same numbers every single brew day. That's also what makes every result on this site shareable: copy the link, and whoever opens it sees the exact same inputs and the exact same computed answer, not a blank form they have to fill in themselves.