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How Do You Properly Calculate Board Footage for a Project
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Q: Is there some magic formula for calculating the wood requirements of a project? Such as a 5/4 x 8" x 8' board has how many board feet? I usually guess (badly) and I either overbuy or go back for more!

Properly calculating board length There's a mathematical formula for determining board footage, allowing you to do all your lumber measurement in peace.

A:Thankfully, the formula is not magic, it’s just math. Think of a board foot (BF) of lumber as 1" thick, 12" wide and 12" long (which is essentially 144 square inches of 1"-thick lumber). So a 1"-thick board, 6" wide and 36" long would be 1.5 or 1-1⁄2 BF of stock. Formula: {(1" x 6" x 36") / 144 = 1.5 BF}.

Rough lumber (hardwood) is sold in multiples of 1/4" thicknesses. So 4/4 lumber (read as four-quarter lumber) is around 1" thick. With any rough lumber thickness, subtract 1/4" to determine the surfaced thickness of the stock. For example, 4/4 lumber will plane cleanly to 3/4"; 5/4 lumber to 1" thick. Note: 3/4" surfaced lumber is considered 1" when calculating BF because it is derived from 4/4 roughsawn lumber.

The thickness of the lumber is the key factor in figuring board feet. The 1" (thickness) dimension is the baseline from which everything else is figured. For example, if you are using 1/2"-thick lumber, multiply the width by .5. In your example, using 5/4 stock, the equation would be: {(1.25" x 8" x 96") / 144 = 6.66 BF}.

Another rule of thumb is that, once you have figured out how many board feet of lumber you need for a project, you will need to add another 20-30% for waste. For a good article on this topic, check out our
http://woodworking.com/ww/Article/Calculating_Board_Feet_7473.aspx site.

posted on July 1, 2011 by Woodworker's Journal
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