This is used in measuring surfaces or things whose length and breadth are considered without regard to hight or depth, as sheeting, flooring, plastering, etc. Fig. 2 shows a square foot. In the measurement of lumber, square measure is frequently termed board measure, and when used as board measure the thickness is considered as one inch. A square is a figure which has four equal sides, and all its angles right angles, as shown in Fig. 2. Hence a square inch is a square the sides of which are each a lineal inch in length. A square foot is a square the sides of which are each a lineal foot in length, as represented in the diagram. A square yard is a square the sides of which are each a lineal yard in length and contains 9 square feet, as shown in Fig. 3. Square measure is so called because its measuring unit is a square. The standard of square measure is derived from the standard linear measure. Hence a unit of square measure is a square the sides of which are respectively equal in length to the linear unit of the same name.

Fig. 1. - Lineal Foot.

Fig. 2. - A Square Foot.

Fig. 3. - A Square Yard.

Fig. 4. - A Cubic Foot.