The word ounce is derived from the Latin word ‘uncia’ which was a unit that measured one twelfth of the Roman pound. It is the commonly used unit of mass in United States.Earlier the measurement of ounce had different standards of mass at different time at different places. But now it is internationally recognized in avoirdupois units. Currently ounce is one sixteenth of an avoirdupois pound. Seven thousand grains makes an avoirdupois pound. Thus one ounce is equal to 437.5 grains.