Convert US gallons to US cups

One US gallon is 16 US cups. To convert any amount, multiply by 16. Going the other way, one US cup is 0.0625 US gallons.

Multiply the US gallon figure by 16. So cup = gal × 16. For a quick mental estimate, multiplying by about 16 gets you within a percent or so, which is close enough for most everyday purposes.

One US gallon is a large jug of milk. The US gallon is exactly 231 cubic inches, or 3.785 litres. The imperial gallon still used in some UK contexts is about 20% larger, which makes fuel-economy comparisons misleading.

One US cup is a standard mug of coffee. The US customary cup is 8 US fluid ounces, about 237 mL. US legal cups are 240 mL, metric cups are 250 mL, and Japanese cups are 200 mL — recipes rarely say which.

US customary. The imperial gallon still used in some UK contexts is about 20% larger than the US gallon, which makes fuel-economy figures misleading when the unit is not stated. Imperial fluid ounces are slightly smaller than US ones, and imperial pints are 20 fluid ounces against the US 16. Cups are worse still: US customary is about 237 mL, US legal is 240, metric is 250 and Japanese is 200 — and recipes almost never say which.

Yes. Since the 1959 international yard and pound agreement, the imperial and metric systems are related by exact definitions rather than measurements — the inch is exactly 25.4 mm and the pound exactly 0.45359237 kg. Everything derived from those, including this conversion, is therefore exact. Round at the end rather than partway through, since rounding gal before converting introduces an error the conversion then multiplies.