How do you convert British recipes to American measurements?
I'm going to assume you're dealing with British Imperial measurements (as opposed to metric).
The main 'gotchas' are cups/pints/quarts, and tablespoons:
US cup = 8 fl.oz. British cup = 10 fl.oz US pint = 16 fl.oz British pint = 20 fl.oz US quart = 32 fl.oz British quart = 40 fl.oz US tablespoon = 14.2 mL ; British tablespoon = 17.7 mL