Most kitchen and bar arithmetic isn't hard — it's just measured in units that don't line up cleanly with each other. A keg is sized in gallons or a regional barrel convention, a bottle needs dividing into pours, a recipe wants butter in "sticks" that only exist in one country, and a volume of water needs turning into a weight for a scale that doesn't do liquids. None of it involves anything more advanced than multiplication and division, but doing it in your head is exactly where the mistakes creep in — usually because the unit you're converting from isn't the one you're used to thinking in. Alongside those container conversions, this section also covers the calorie and macro arithmetic behind eating for a goal — how many calories a day, split into what ratio of protein, carbs and fat, and what a given amount of exercise or alcohol actually costs against that budget.
Calculators in this section
Containers that don't convert to round numbers
The beer volume calculator and the wine volume calculator both solve the same basic problem — how many servings come out of a container — but the containers themselves are the awkward part. American keg sizes are defined in gallons against a 31-gallon barrel, and converting that to liters never lands on a tidy figure: a sixth-barrel keg is 19.5 liters, a quarter-barrel is 29.3 liters, a half-barrel is 58.7 liters. European kegs, by contrast, are commonly sold in genuinely round metric sizes like 30 or 50 liters, which are close to but not the same as their American counterparts — close enough to cause a mistake if you assume they match. Wine is more forgiving, since a standard 750 ml bottle and a roughly 150 ml pour are figures most people already carry around, but even there, pour sizes vary enough between a home measure and a generous restaurant glass that the number of servings per bottle isn't quite fixed either.
Butter sticks are an American unit, not a universal one
The butter calculator exists because of a specific, common mismatch: US recipes measure butter in sticks, cups and tablespoons, all based on the markings printed on a US butter wrapper, while butter almost everywhere else is sold in solid blocks by weight — 250 g or 500 g, with no stick markings at all. Anyone following a US recipe outside the US, or converting a European recipe's gram figure into something a US wrapper can measure out, needs the stick-to-gram relationship to do it accurately rather than guessing.
Weight from volume, for one specific liquid
The weight of water calculator is the odd one out in that it isn't really a unit-mismatch problem — it converts a volume most people think of in liters into a weight most kitchen scales expect, which is genuinely useful when a recipe, an aquarium, or a shipping estimate gives you one and needs the other. It works cleanly for water specifically because water's density is close to exactly 1 kg per liter; the same shortcut does not carry over to milk, oil, syrup or anything else with a different density, so it's worth treating as a water-only rule of thumb rather than a general liquid-to-weight conversion.
Calorie, macro and diet planning
The rest of the section works out the numbers behind eating for a specific goal, once basal metabolic rate and activity level are on the table. The calorie calculator and macro calculator turn BMR and activity into a daily calorie target and a protein/carb/fat split; the calorie surplus and weight loss calculators apply that same base arithmetic in opposite directions, for gaining or losing at a chosen weekly rate. The calories burned, carbohydrate and fat intake calculators break out specific pieces of that budget, and the intermittent fasting and alcohol calorie calculators cover two things that don't fit neatly into a macro split: a fasting/eating clock, and the calories hiding in a drink. This site's health section already covers BMR, TDEE, water intake, fibre, keto macros, protein intake and calorie deficit on their own — those aren't repeated here to avoid two calculators answering the same question.