The calculations you actually reach for: how much to tip, how much paint the room needs, how to scale a recipe without ruining it, how long the download will take. These are the most-used tools on the site and the ones most likely to be done roughly — so each one shows its formula, applies the correction that usually gets missed (the 10% wastage, the 8 bits in a byte), and works a full example. Everything runs in your browser, free and without signup.
Scale any recipe up or down, with unit conversion and baker's percentages.
Open →Kitchen units for weight: grams, ounces, pounds, kilograms and more.
Open →Convert cooking measures between metric and US customary, including scaling.
Open →Floor area, wall area and volume, plus paint, flooring and tile quantities.
Open →Gallons for a room minus doors and windows, per coat count.
Open →Exact age in years, months and days, plus the next birthday.
Open →Days between dates, add or subtract days, and find any weekday.
Open →Tip amount, total bill and per-person split at any percentage.
Open →Split a bill evenly between any number of people, with or without tip.
Open →The most-used calculators on the site are the ones nobody thinks of as mathematics: how much to tip, how long a download takes, how much paint a room needs. This section collects them, and adds the ones the site was missing.
Area is length × width — the floor, for flooring or a ceiling. Volume adds height, giving the air space, which matters for heating, ventilation and acoustics. The two answer different questions and confusing them is the most common error.
Subtract doors and windows from the wall area, add about 10% for wastage, and divide by 10 m² per litre (or 350 ft² per gallon). A typical 20 m² room needs roughly 5 litres for two coats.
By weight whenever possible. A cup of flour and a cup of sugar differ in mass by around 60%, so volume-based scaling does not preserve the recipe's character, while weight-based scaling does exactly.
No. Every calculator on the site runs entirely in your browser, so they work offline and nothing you enter is uploaded anywhere.