Calculating Waste from Rough Lumber

      You always lose some ... here's a look at the numbers. December 2, 2010

Question
I have always used a 30% waste factor when ordering lumber for five piece doors with solid panels. I usually end up with about 10% not used on project. I might keep few nice boards for inventory, and pick out a few ugly ones. I have a small shop and this does not slow us down much. I am curious how others figure waste percentage and the ugly lumber in orders 500 bf and under? Stile and rail size, cut, and wood species factor in to yield but the average for us is 2 3/4" plain cut, select.

Forum Responses
(Cabinetmaking Forum)
From contributor U:
In building shutters we allow 10% cutting waste from the actual milled parts. We allow another 10% for turning the raw lumber into parts for the final cutting process. When placing the order with my supplier, I add another 10% just to allow for their quirks and possible freight damage, board sizes that won't work for this particular project. The 10% cutting waste helps me quote more accurately, the processing waste covers just that, but usually the last 10% ends up as inventory and backup supply. The great thing is that about once a month I can build a small order from the buildup of inventory and have almost no cost of materials.



From contributor F:
If you have 30% waste then you need to purchase 142.85 board feet to get net 100 feet
100-30=70
100/.7=142.857

Or 100/70=1.42857
1.42857*100=142.857

By adding on your waste factor isn't 30% you are purchasing 30% more material? Adding 30% on is a 23% waste factor which is extremely high yield unless you are purchasing material that is S4S to widths you need. If when you order you always have enough material then you method works but itís not really a 30% waste factor.



From contributor T:
It took me a while to understand why your formula works and now I know why when I would purchase 30% more I would usually come up short. Thanks for the math lesson, I will remember this one.


From contributor F:
I should have added these lines:

142.857*30%=42.857
142-42.857(waste) = 100

Itís really the same concept as a profit margin, if you want to get a 10% profit you divide the number by .9.



From contributor T:
I followed the point of just adding 30% to 100bf only gives you 130bf. But, you still have waste coming off the 30% which will bring you below your desired 100bf yield. No problem. I have always just multiplied by 30% and added it on. Your formula showed me the way. Now, as for your profit, I am lost. If I want 10% profit on a $100 then I just add 10% arriving at $110. Using your formula of dividing by .9 gives me $111.11. I am confused now. I do love learning new stuff (for most this is probably really basic though).


From contributor F:
Adding on is markup, dividing by the factor results in a desired margin. Using margin gets you a target goal (10% profit or 30% waste). If you added 10% to 100000 your profit would be 10,000 but the sale is 110,000 and the profit margin would be about .0909. If you want to use markup and get 10% use 11.11% to add on.


From the original questioner:
Thanks for the math lesson. Youíre right I am just adding on 30% more lumber to the finished door sq. footage, which is actually 23% waste or extra. This has seemed to work for me in the past, and I donít recall having to order more lumber to finish a project any time recently. What is your "waste/overage" percentage? What is average? 30% or 40%?

From contributor F:
For rough lumber the average is 50%. This is calculated as 1" green to 3/4" finish = 25% loss. You lose another 5-15% in straight line and end cuts and the rest is yield and defects. If you purchase s3s or s4s the waste is in the price you pay. 90% of what we buy is in the rough. Right now we are running a large amount of moldings so we are able to go from widest to narrowest and longest to shortest so our yield is pretty good and we are having the distributor pick for lengths we can use but we don't count on that for small projects.



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