Convert US cups to US fluid ounces

One US cup is 8 US fluid ounces. To convert any amount, multiply by 8. Going the other way, one US fluid ounce is 0.125 US cups.

Multiply the US cup figure by 8. So fl oz = cup × 8. For a quick mental estimate, multiplying by about 8 gets you within a percent or so, which is close enough for most everyday purposes.

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.

One US fluid ounce is a small shot glass. The US fluid ounce is 1/128 of a US gallon, about 29.6 mL. The imperial fluid ounce is 28.4 mL — close enough to confuse, far enough apart to ruin a recipe at scale.

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 cup before converting introduces an error the conversion then multiplies.