As a starting point, add 15 percent to your bill of materials. Then consider your project design. If there are odd-shaped parts, add 5 to 10 percent to that number. Add to that another 5 to 10 percent if you'll use sapwood-prone species, such as walnut or cherry. If you're shopping in the lower grades of wood—No. 1 or 2 common—you'll need to tack on an additional 30 percent to your order due to defects. That may sound like a lot, but it really makes sense when you realize that you could save up to 50 percent over Firsts and Seconds (FAS) lumber.Finally, keep in mind that the wood you see in the bin at your hardwood store today could come from a different, mismatched source tomorrow. So buy a little extra—being too obsessive about avoiding all waste could hurt the look of your project if you need to make a return trip.—from the WOOD® shop