Forum weight log calculator

[Ron Wenrich]

I had a bit of a discussion with Danny about our saw log weight calculator.   He had a couple of logs that he weighed, and the calculator seemingly underestimated the weight.  He had the opportunity to cut the logs in half, so he had a pretty good midpoint measurement.  He has a USFS research paper on the subject:
https://www.nrs.fs.fed.us/pubs/rn/rn_nrs38.pdf   After looking at it, I had to figure out how I made the calculators 15 years ago. 

I looked at the data for the cubic foot weight by species.  My calcs use green weight, as does the study.  So, the difference has to be in 2 different areas.  One is bark volume and the other is in measurement. 

There are several ways to measure cubic foot volume in a log.  There are 3 formulas to chose from.  The Huber formula uses a midpoint log measurement.  The Smailian formula uses a small end and large end measurement.  The Newton formula uses the ends and midpoint measurements.  Newton is more accurate, but harder to measure.  Smailian overestimates volume and requires more measurements.  Huber underestimates and use only 1 measurement.  None of the options are quite ideal under field usage.  I went with the Huber for ease of measurement and estimation. 

I looked at bark weight.  Bark is a tricky thing.  It varies in thickness and sometimes it isn't there.  I looked at the weight of bark, and in most instances the bark is a bit heavier that wood.  The percentage of bark to wood weight ratio in a log will vary to as little as 8% in sycamore to 22% in many of the oaks and 25% in some of the pines.  I could alter the weight density, but the lack of bark would skew it pretty hard.  Given that bark isn't a whole lot heavier and doesn't comprise a lot of volume, I looked to how things are measured to see if there is any opportunity to give a better result.

We've had it driven in our head that all measurements are from the inside of bark.  To get a better weight result, the bark should be included in the measurement.  This should make it easier to estimate diameter at midpoint.  There is no need to guess the bark thickness and then double it to get an inside measurement.  Using a caliper, it should be fairly easy to get the outside measurement, even on an odd shaped log.  You will still be a bit under estimate, but it shouldn't be as drastic as omitting the bark.

I believe Danny originally used a diameter inside bark to get his midpoint estimate.  The weight came up about 18% short from an actual weighing.  That is about the weight of the bark given the ratio.  I ran the numbers back and figured bark to be about 1", given the size of the logs.  The weight came in about 3% shy of the actual weight.  So, I think measuring outside bark should give a better estimate for actual weight than measuring inside bark.  Just something to keep in mind. 

[Percy]

Over the years I have used that tool and while I was happy with the results, there still is a bit of Las Vegas when estimating any green log. Got a swamp grown WRC that was from another planet.

[WDH]

The bark, or lack of it, is important in calculating the weight of a log if you do not have access to a weigh scale.  It can affect the results by 10% to 25% depending on species.  Bark % on a log changes with log size, so things can get complicated pretty quick.  There is nothing easy about trees (new old saying).

[Magicman]

I compared the FF weight calculator with my iPhone (Bartlett) weight calculator app today before I even noticed this topic.  They were within 100 pounds of each other.

[4x4American]

If you got the logs from around here you also gotta add all the mud they pack on to them lol

[YellowHammer]

I've used it and and others, and discussed with WDH.  I generally know what species I'm getting before I'm loading, and so I go ahead and calculate an allowable approximate boardfootage before I leave the house to get me to max payload weight.  Then, when I get to the mill, I tell them to load me with about that amount of logs.  They keep a running tally of the boardfootage as they load.  I have a set of certified scales I drive over when I leave the mill so get a true weight.  I've been way under, and way over, and there isn't anything much worse than being overweight and either having to return to the mill to take logs off, or risking the drive and a having a very painful and expensive talk with a State Trooper. 

[Magicman]

Since I do not transport anything, I mostly use it to calculate whether my sawmill loader will pick up a log.  I occasionally have a customer to ask about the weight of lumber to keep from overloading a trailer.

[GeneWengert-WoodDoc]

A butt log, especially a larger one, will have higher moisture content (as much as 30% MC higher or as much as 600 pounds per 1000 BF) which means higher weight, than the average.  Upper, smaller logs can be below the average.

Southern grown species that are ring porous (oak elm, ash, etc.) will be heavier than northern or Appalachian.  No problem with non-ring porous, like maple, basswood, etc.

[WDH]

Southern grown species that are ring porous (oak elm, ash, etc.) will be heavier than northern or Appalachian. 

That is because they grow faster  .