A recipe scaler for any batch size, up or down

Why the answer is rounded to a fraction rather than given exactly

Scale 0.75 cups by 1.5 and the arithmetic says 1.125 cups. Nobody has a 0.125-cup measure, and in practice a cook will pour something close to one and an eighth and move on. So this tool snaps the result to the nearest fraction a kitchen actually owns - Eighths, quarters, thirds, halves - And shows the exact figure underneath in case you are weighing.

The recipes on this site do the same thing on their 1×/2×/4×/8× tabs, which is why those particular multiples were chosen: doubling and quadrupling produce clean fractions, where scaling by 1.5 or 3 frequently does not.

The things that do not scale linearly, and this is the important part

Multiplying every ingredient by three does not produce three times the recipe. Four things break:

• Salt and strong spices scale sub-linearly in a long-cooked dish. Doubling a chilli and doubling its salt gives something noticeably saltier, because reduction concentrates what is already there. Start at 75 per cent of the scaled figure and adjust at the end.
• Cooking times do not scale at all for anything with a surface. Eight burgers take the same three minutes a side as two; they just will not fit in one pan. Cook in batches rather than crowding, because a crowded pan steams.
• Cooking times do scale for anything with a mass. A double batch of chilli in one pot takes considerably longer to come to temperature and longer to reduce. Allow half as long again.
• Raising agents scale linearly but the tin does not. Doubling a cake batter and putting it in one tin gives a cake twice as deep, which needs a lower temperature and a much longer bake. Two tins is almost always the right answer.

Every recipe on this site that has a scaling caveat says so on the page itself, in the batch-size section. The tabs handle the arithmetic; the prose handles the judgement.