The four things every recipe makes you look up: cups to grams (per ingredient, because a cup of flour is not a cup of sugar), oven temperatures between °C, °F, fan and gas mark, the equivalents that save a trip to the shop, and what to use when you have run out of something. Works offline, in the kitchen, with floury hands.
Cup measures use the metric cup of 250 ml used in the UK, Australia and New Zealand. A US cup is 240 ml, so a US recipe's cup is about 4% smaller — rarely decisive in a stew, occasionally decisive in a sponge. Weight-to-volume figures are typical packed values for the ingredient as you would spoon and level it; flour scooped straight from the bag and compressed can weigh 10–20% more, which is exactly why serious baking recipes give grams.
Fan ovens circulate air and cook hotter for the same dial setting, so the usual rule is 20 °C lower than the conventional figure in the recipe. Gas marks are the standard UK scale (mark 4 = 180 °C = 350 °F). Home ovens vary by 10–20 °C from their dial, so an oven thermometer beats any conversion table.
Substitutions are for cooking, not for allergies or intolerances: swapping one dairy or gluten product for another does not make a dish safe. Check the label. Nothing here leaves your device — no network request is made.