Estimating Lumber Quantities. Lumber is measured in terms of the board foot as a unit, 12" by 12" by 1" or its equivalent, indicated by the abbreviation B. M. (board measure).


Determine the B. M. in a girder 6" by 8" by 16'.


Rule - Thickness in inches times width in inches, divided by 12" times the length in feet gives a number equal to the number of board feet.

6"x 8"

6"x8"/12 X 16' = 64' B.M.

Stock less than 1" thick is figured as 1" thick. In commercial practice lumbermen make use of tables in determining quantities. Appendix III.

In estimating quantities, suitable allowance must be made for waste. This waste is incurred (1) thru loss when boards or planks are cut to required lengths. Standard lengths are 10', 12', 14', etc., and these will not always cut to advantage. (2) Waste is incurred in machining the stock, as dressing, edging, tonguing and grooving. Necessary allowances will be indicated herein.

Heavy Timbers

Girders, posts, etc.,are determined by count.


To determine the number of joists required for a room or a building, count the actual number required beginning at a wall ( times number of feet in length or width of room when set 16" on centers), and to this add one joist to be placed against the second wall.

Cataloged or listed sizes are for lumber fresh from the saw. Shrinkage due to seasoning and surfacing one side and one edge so that the stock may have uniform thickness and width will give actual sizes as follows: 2" x 4" when sized on one side and one edge, will give 1⅝" x3⅝"; 2" x 6",S-l-S and I E, 1⅝" x 5⅝"; 2" x 8", S-l-S and I E gives l⅝"x7"; 2" x 10", S-l-S and IE gives 1⅝"x 9"; 2"xl2", S-l-S and IE gives 1⅝ x 11. When

5-2-5 and 2E. or sized on 4 sides, stock will measure ⅛" less than indicated above.

Studs For Walls And Partitions

Count one for each lineal foot of wall or partition, where specified 16" on centers. The extra studs are to be used in doubling corners, at doors and windows, and in gables. Barns and sheds will not require these extra studs.


Allow 25 lineal feet of 2" by 4" for each square of flooring.


On a plain roof, count actual number and add one, as in counting for joists.


Calculate the exact surface to be covered, deduct openings; then, for unmatched sheathing or barn boards or fencing, as it is also called, add 1/12 for 12" boards, 1/10 for 10" boards and ⅛ where 8" boards are used. Four inch and 6" are seldom laid solid, being used mainly for roof sheathing for shingle roofs, and laid 2" apart. These additions are due to the fact that thru seasoning and dressing, a 12" board becomes 11", a 10" becomes 9⅝", an 8" becomes 7", a 6" becomes 5" and a 4" becomes 3". The additions specified allow for waste in cutting.


Calculate the exact surface to be covered, deduct openings; then add for floors 17%, for sidewalls 20%, for roofs 25%.

Sheathing laid with 2" spaces should have proportionate deductions made, that is, on l"x6", figure as if laid solid, then deduct ; for 1" x 4" deduct ⅓. Sheathing when matched, such as is used sometimes for sub-floors and side walls and roof sheathing under slate roofs and better known as flooring, will be estimated by figuring the exact surface to be covered, deducting the openings, then adding for 6" stock, which is the kind most always used, 15% for floors, 17% for sidewalls, and 20% for roofs.

If shiplap or matched sheathing is laid diagonally add 5% for waste due to lack of ability to reverse cut.


For bevel siding, calculate the exact surface, deduct openings; then add for 6" siding when laid 4" to the weather, 33%; for the 4" siding add 50%.

Drop Siding

Drop siding, ceiling and wainscoting are figured just like matched flooring, which is described below.


For square edge, calculate the exact surface to be covered, add for 6" flooring 11% for waste in matching, etc.; for 4" flooring add 20%. It is becoming common practice to specify flooring by actual face measurement after being machined. The following figures are for actual surface measurements.

For matched flooring, calculate the exact surface to be covered, then add 20% for 5 " flooring, for 3 " flooring add 25%, for 2 " add 33%, for 1" add 40%.

Flooring less than 1" thick, like all other lumber, is estimated as 1" thick.


A bunch of shingles contains the equivalent of 250 shingles of 4" average width. With an exposure of 4" to the weather a 4" average shingle will cover 18 square inches, making 800 shingles to the square. Waste in doubling the first course and in laying will necessitate an addition of 8% on a plain roof and 12% on hips or on gabled walls. Cost estimates are based upon the M. or 1000.

SHINGLES PER SQUARE Plain roof, 4 * exposure, 990; roof cut up, 1010 Plain roof, 4" exposure, 880; roof cut up, 900 Plain roof, 5 " exposure, 790; roof cut up, 810


Lath for interior plaster work are usually ⅜" by 1⅓" by 4', put up in bundles of 50 each and are sold by the 1000. 1000 lath will cover 70 yards of surface and will require 8 lbs. of 3d fine lath nails. Lathing is usually considered a part of the plasterer's contract. There is no uniformity of practice as to the deduction for openings.

Building Papers

The cheapest is "rosin sized," and is not waterproof. This is used mainly under floors and upon side walls under bevel siding. It is sold by the pound in rolls each 36" wide containing 500 square feet.

Dry felt is used where better protection from cold is desired. In the cheaper grades, the material is made of wood fiber and rosin. In the better grades wool is used. Tar felt, used where moisture is to be resisted, is dry felt saturated with tar. These materials are sold by the pound: 12, 15, and 20 lbs. to the 100 square feet, in rolls of various widths. A catalog should be consulted for weights and covering capacity.