A square of slate or slating is 100 superficial feet.

In measuring, the width of the eaves is allowed at the widest part. Hips, valleys, and cutting are to be measured lineal, and 6 inches width extra is allowed.

The thickness of slates ranges from 3-16 to 5-16 of a inch, and their weight varies from 2.6 to 4.5 lbs. per square foot.

The lap of slates varies from 2 to 4 inches. The standard is assumed to be 3 inches.

To compute the number of slates of a given size required per squares.

Subtract 3 inches from the length of the slate, multiply the remainder by the width and divide by 2. Divide 14.400 by the number so found, and the result will be the number of slates required.

The pitch of a slate roof should not be less than 1 in. height to 4 in. length.

Dimensions of slates and numbers required to a square. 12x6 requires 533 to the square; 14x9 requires 291; 18x9 requires 213; 24x13 requires 105.