How to Calculate Lumber for an Addition

When calculating the amount of lumber for an addition, follow a detailed set of plans and remember that most lumber comes in 16-foot lengths. Unless you pick your own boards some of the wood you buy will be unusable because of ragged ends, cracks or bowing, which is warping along the length of the board, or cupping, warping across the width of the board. Slight defects are not usually critical in framing timbers but are important in any visible wood in the addition. Calculate the required amount of lumber by counting the individual boards you need.

Detailed plans for your addition
Calculator

Instructions

- 1
  Count the total number of boards of each nominal size, like 2-by-4s, 2-by-8s and 2-by-2s, you need based on detailed plans for your addition. Keep separate calculations for each board or timber size.
- 2
  Count the number of all studs, sills, stringers and every other component of your addition.
- 3
  Note the lengths of all the boards you will cut. For example, if you plan to use vertical studs that are 7 feet 10 inches long, cut two studs from each 16 foot long board.
- 4
  Calculate the lineal feet of for all the waste boards. For example, if your addition includes 14 foot long stringers or joists, you will waste 2 feet of lumber for every stringer or joist.
- 5
  Add the lineal feet of all the wood you will use, waste and that will be unusable.
- 6
  Translate your order from lineal feet into board feet if your lumber yard prefers to bid on your order in board feet. Board feet equals the actual length in inches multiplied by the nominal width in inches multiplied by the nominal height in inches and then divided by 144.

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