US tablespoons to US cups (tbsp to cup)

One US tablespoon is exactly 0.0625 US cups. That ratio belongs to the customary system itself and is much older than any link to metric: the 1959 international yard and pound agreement later fixed the yard and the pound against the meter and the kilogram, but it left the ratios between customary units (feet to the yard, ounces to the pound, cups to the gallon) exactly as they were.

Worked through: 6 tbsp x 0.0625 = 0.375 cup.

Going the other way, one US cup is 16 US tablespoons.

For mental arithmetic: Divide by 16.

Divide by 16. This is the direction for scaling a recipe down or for working out whether it is worth getting the measuring cup out: 4 tablespoons is a quarter cup, 8 is a half. Note that the tablespoon is not standardized internationally: the US one is 14.79 ml, the UK one 15 ml and the Australian one 20 ml, which is four teaspoons rather than three. An Australian recipe's tablespoon is a third more than an American one's, so a cup holds about 12 of them rather than 16.

Precision is worth matching to the input. A measurement given as 1 tbsp carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.