Brewing math, done properly.

Why this site exists

Brewing calculations are most useful when the units, measurements, and assumptions are clear. This site keeps your equipment profile alongside the tools and shows the arithmetic behind a result.

Some accepted brewing formulas produce different estimates. The IBU tools show Tinseth and Rager side by side, for example. Showing that difference helps explain a recipe comparison without implying that either estimate is a laboratory measurement.

Who's behind it

I'm Brian Hamilton, and I build every calculator on this site. I'm not a professional brewer, and I'm not going to pretend to be one. I build calculation tools for a living — thirty years of software development, an internet engineering degree, and a stretch building mathematical models for sports prediction companies. This site is that work pointed at wort.

My contribution is software engineering: implementing the formulas, testing conversions and edge cases, and making the tools practical to use. Brewing involves biology, ingredients, equipment, and sensory judgment that a calculator cannot fully represent. The articles link to brewing researchers, laboratories, and manufacturers for those subjects.

Where brewing expertise is required, I lean on the people who have it and say so by name — see the sources below. And where I'm uncertain, the site says it's uncertain rather than rounding up to confidence: the IBU page shows both formulas disagreeing, the refractometer page calls its corrections regressions, and the pitch-rate page prints the estimated range in how many cells a dry sachet actually contains.

BrewToolbox is one of a family of Toolbox calculator sites I build — pools, brewing, cycling, RVs, soap making and more — alongside the puzzle games and apps I've worked on for years. My author profile has the longer version.

The company behind the site

BrewToolbox is published by Hamilton Digital Media Limited, which publishes puzzle games, apps and books, and builds practical online tools and calculators. It's a small UK company, and it's the legal entity that answers for this site — the one named in the terms and privacy policy.

Sources and limits

The brewing science here isn't ours and we don't claim it. Hop utilization includes Tinseth and Rager estimates based on Glenn Tinseth's published curves and Jackie Rager's earlier ones — both shown, because recipes were written in both. Mash and infusion math follows John Palmer's How to Brew; extract potentials and recipe formulation lean on Ray Daniels' Designing Great Beers. Gravity, real extract and calorie methods are the American Society of Brewing Chemists'. Pitching rates follow Chris White and Jamil Zainasheff's Yeast. Refractometer corrections use Sean Terrill's fits and Novotny's later refit. Malt and yeast figures come from maltsters' and labs' own data sheets.

Our contribution is the implementation, the testing, the equipment profile that makes the numbers yours rather than generic, and the writing — plus a stubborn insistence on showing the arithmetic so you're never asked to take a number on faith.

Corrections are welcome

If you find a mistake in a calculation, recommendation, or article, corrections@brewtoolbox.com goes straight to a person. We review reports, correct confirmed errors, and note material corrections on the affected page.

Models have limits, hop lots vary, and manufacturer specifications change. Accurate measurements and current product instructions matter alongside the arithmetic.

What makes this different from the other calculators

• Set up once, remembered everywhere. Your batch size, efficiency and losses live in your browser and feed every tool — no account, no login, nothing to sign up for.
• Both formulas, side by side. Where the standards disagree — Tinseth and Rager, the two ABV equations, the refractometer fits — you get both and an explanation of the gap.
• US and metric, equally. Liters, kilos and °C aren't a toggle bolted on afterwards. The engine is metric inside and converts at the edges, so a metric recipe isn't a second-class citizen.
• Fast, static pages. No app shell, no spinner, no waiting — it works on a phone in a cold garage.
• The math is shown, and it's checked. Every page cites its source and shows its arithmetic, and the engine behind them is tested against published values.

How the site makes money

Some links to equipment will earn a commission at no cost to you. That's the whole model — no ads that follow you around, no paid reviews, no sponsored placements, and nothing gated behind a signup. The rules are written down in the affiliate disclosure, and the important one is this: the math picks the recommendation, and we say so when the cheap option is the right one. Plenty of the best answers in brewing — a $10 hydrometer read correctly instead of a $60 refractometer read wrong, a bag in a pot instead of a three-vessel rig, $30 of temperature control before $900 of shiny kettle — earn us almost nothing. We publish them anyway, because a site that recommends whatever pays best gets read once.

As it happens, there are no affiliate links on the site at all yet. The calculators came first.

What's here, and what's coming

34 calculators and 9 guides are live. Brew Day includes planning, timers, brew-day measurements, and a fermentation log. The calculator directory and guide directory list the current pages.

Your equipment is remembered in your own browser so you don't retype it every visit — and it never reaches us, which is the sort of thing that's easy to promise and easy to verify: the privacy policy lists exactly what's stored on your device right now, and there's a button there that deletes the lot.