A 12-inch ruler has numbers and a line for every inch. Between each inch mark, there are fraction lines. The length of the line corresponds to the size of the fraction. A standard ruler has marks for the inch, half-inch, quarter-inch, eighth-inch and sixteenth-inch.
Twelve-inch rulers rely on fractions for measurement. When counting fraction lines, include all lines of equal or bigger size. When counting quarter inches the half-inch mark counts as the second quarter inch mark.
To measure an object, line up the end of the ruler with the lower value with the end of the object to be measured. Next, find the line on the ruler that coincides with the end of the object. The length of that object is equal to the last inch marker plus the fraction markers.