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how much wood per tree length

Post in 'The Wood Shed' started by henfruit, Feb 13, 2009.

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  1. henfruit

    henfruit Minister of Fire

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    was wondering,how may logs at 15 ft. long and 12 inches in dia.would it take to have a cord of wood4X4X8.

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  2. fossil

    fossil Accidental Moderator Staff Member

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    Oh...8 or 9, I s'pose. Somewhere in there. Rick
  3. vwboomer

    vwboomer New Member

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    er. 9ish by my new math
  4. Got Wood

    Got Wood Minister of Fire

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    8.5
  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    All correct.
  6. Corey

    Corey Minister of Fire

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    I guess I'm coming up with a little different answer:

    pi x radius^2 x length = cubic feet of wood per log

    for a 15 foot x 1 foot log:

    3.14 x .5 ft ^2 x 15 = 11.77 cubic foot of solid wood per log

    http://firewoodresource.com/articles/cord.html

    So:

    Max = 90 cu ft / 11.77 = 7.6 logs

    Avg = 80 cu ft / 11.77 = 6.8 logs

    Min = 70 cu ft / 11.77 = 5.9 logs
  7. fossil

    fossil Accidental Moderator Staff Member

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    Just to be safe, bring home 8.462 of those logs. Rick
  8. vwboomer

    vwboomer New Member

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    There is no airspace in the log.
  9. Eric Johnson

    Eric Johnson Mod Emeritus

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    I calculated how many of those logs it would take to make 1,000 board feet and cut the number in half, since there are generally thought to be about two cords per MBF. That's a very rough measurement (different log scales yield different BF totals for the same logs), but I came up with 8.5. So it's somewhere between 8 and 9 logs, by that measure.
  10. fossil

    fossil Accidental Moderator Staff Member

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    Actually, there's more than you might think, especially as it seasons. But that's not the airspace we're talking about. Even if you stack those logs just as they are, the stack you come up with is not going to contain solid wood within it's exterior dimensions. A cord of wood is typically defined, as you stated, as 128 cubic feet of neatly stacked split wood. A 4'x4'x8' stack fits the definition. That neatly stacked cord of wood is going to have anywhere from 15% to 30+% airspace in it. So your 128 cubic foot cord will actually contain maybe ~80 or 90 cubic feet of wood, as cozy said. In any case, the answer to the OP's question seems to be ~ 8 or 9 of those logs should yield about a cord of split & stacked firewood. Rick
  11. Eric Johnson

    Eric Johnson Mod Emeritus

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    And it's going to shrink as it dries. Some people thing that's a negligible factor, but if you have a good pile of wood--say 10 or 20 cords, you could easily lose the better part of a cord as it dries. That's one thing people don't realize about the firewood business--dry wood costs more not only because somebody sat on it long enough for it to dry, but they wind up with less wood than they started with, and have to add more to make it come out to a full cord for the customer.
  12. fossil

    fossil Accidental Moderator Staff Member

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    ^ Yup. Not so much in length so's you'll notice, but most certainly in breadth. I've had perfectly stable stacks teeter as they seasoned, because of the shrinkage of the wood. Rick
  13. Eric Johnson

    Eric Johnson Mod Emeritus

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    I figured out how much at one point, but the thread was lost on the old forum (before we got this fancy software) and it's gone. I stack my wood 6.5 feet high, and I think a green stack shrunk down to something like 6' over the course of the summer and fall. So that would be 7.6%. Nothing to sneeze at. That's 3/4 of a cord lost for every 10.
  14. fossil

    fossil Accidental Moderator Staff Member

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    Nothing to sneeze at, fer sure, but it's a good thing, and what seasoning's all about...getting that nasty moisture out of the firewood. Yes, a cord of wood stacked green turns into less than a cord of seasoned wood, but I'll live with that. Rick
  15. Eric Johnson

    Eric Johnson Mod Emeritus

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    I work with a lady who had a dog once that would steal wood from the neighbor's pile and bring it home. I think they trained him to do that, though they deny it. So losses are not always limited to drying.

    Another friend had a dog that would run in front of you and break trail on backcountry skiing trips. It was great for the most part, except that sking around in those tight little circles periodically would get a little old. That and chasing rabbits.
  16. LLigetfa

    LLigetfa Minister of Fire

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    Ja, I stack my wood 9 feet tall in my woodshed and I've seen that phenomenon when I stacked very green wood rows right tight together. As the face row shrank, the edges would catch on the previous row and also the exposed face dried and shrank at a faster rate than the backside causing the face of the last row to curl away and topple.

    I stack right tight to the rafters and have seen as much as a 9 inch gap form as it shrank. Given the height of 9 feet, that is about one inch per foot so 1/12th or 1 cord lost in 12 cord to shrinkage. I don't usually stack green wood in the shed, preferring to leave it loose piled out in the sun and wind for a few months first. Here are a couple of pics of wood that sat out first. There is less than 4 inches of gap.

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  17. wendell

    wendell Minister of Fire

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    Thanks, guys. Now I don't feel so bad about that stack of maple that is sagging against the neighbor's fence!
  18. jimnj

    jimnj New Member

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    A good source of info for log scaling :http://www.for.gov.bc.ca/hva/manuals/scaling/pdf/Ch4.pdf

    cozy heat has the right answer at 11.77 cu./ft. per log

    I put a spreadsheet together for buying logs using Smalian's log scaling formula

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  19. kenny chaos

    kenny chaos Minister of Fire

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    Using a different method: My woodlot tables shows one log would be .145 cord or 6.9 trees for a cord.
  20. fossil

    fossil Accidental Moderator Staff Member

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    It's not difficult to calculate the volume of a cylinder. It is very difficult to find a log that's a cylinder. After the log is bucked, split, and stacked, there will be a neat stack of wood that came from the log. The stack will have a significant percentage of empty space in it...depending on the size, straightness, and shape of the splits, and how tightly the wood is stacked. There's nothing whatever precise about this, it's all just estimation. Rick
  21. kenny chaos

    kenny chaos Minister of Fire

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    Actually, the estimate was 6.9 logs. The real answer is 6.896552. :coolsmile:
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