Log scale and overrun

Different types of scales, formulas and methods of figuring overrun. January 28, 2002

Q.
Have you read the article in the Nov/Dec 2001 Tree Farmer magazine by Jim Conway, "The True Tally"? I must be missing something--I have never scaled a log and gotten a 100% overrun! I scale the log as honest as I can. I use the 1/4 int. scale. I am fair to my loggers. Yes, I may get some overrun, but it makes up for unseen defects. The northern red oak I paid $400 a m for had a bad heart. Nothing on the outside gave me a clue--I have never seen a log like it. What am I missing?

Forum Responses
I use the Doyle scale and consistently double my footage, sometimes even triple it in small straight logs. I'm fair to the loggers I deal with. I buy a bark and they give a bark. In the small logs (7inches and under), if they are straight, I'll pay the logger log measure plus the length of the log to make it worth their while to fool with them and I still double my money after they are sawn. It depends a lot on the way you saw. I saw conservatively, so I gain a lot of footage.

I've bought spotted oak similar to what you described. It looks good on 4 sides and the ends look good but when it's opened, it's full of carpenter ants that ruin the lumber. Sawing it is like shooting craps.


Scaling logs is done from the small end of the log inside the bark. Diameter is measured twice (at 90 degrees to each other) and averaged. Unusual swelling is ignored--we are trying to measure the small end diameter of the merchantable bole. Log length is to the last full foot (i.e., no fractions). Then use a table or formula or log scaling stick to get the volume in BF. With the Int 1/4 inch rule, you will have a fairly accurate estimate of the footage at all diameters and lengths when sawing 1-inch thick lumber; in other words, zero overrun. It assumes a 1/4" kerf, so a thinner blade will improve the overrun by 10%. If you are getting double the footage predicted, something is wrong with the way you are scaling and using the International 1/4 Inch Rule. Even when cutting thick pieces, you will not be able to double the output.

Sometimes when scaling, we deduct a certain amount of volume from the gross scale described above to obtain a net footage. There are specific rules on how to do this.

Example: If you have a log that is 13.7 inches for one diameter and 14.9 for the other at the small end, inside the bark, and the log is 12' 8" long, what is the footage using the International 1/4 Inch Scale? Using the Doyle Scale?

Gene Wengert, forum technical advisor


From contributor A:
That would be a 14 inch 12 foot log and would contain 100 bdft on International 1/4 scale, 75 bdft Doyle scale, 90 bdft Scribner C scale. Cost me about $18.75, take 30 min to saw and pay me about $54.

In inches take the inside measure, in feet take the length of log. Divide inside measure by 1.4 then square the number. Multiply by length and divide by 12 and you have bdft. (About same as 1/4 International.)

I find that if I do the number by 1.3 instead of 1.4 I get real close to what I will get from a good straight log. A 14" x 12' log I would expect about 120 bdft of lumber.


Cool! Thanks--I give you an A+.

Gene Wengert, forum technical advisor


From contributor M:
Here in western WA it's the Scribner scale, and I just realized the other day how the mills around here can pay so much for logs. In the long lengths, especially on flare butted trees, and especially in the smaller diameters, the Scribner isn't even close. I scaled some hemlock that I'm cutting at 1500bf (36-40' logs) and then cut it all into 8 and 10' logs and I am approaching 100% overrun. When I did portable work in CA, people had already cut their logs down to 12-20' usually and then I would get only about 125% overrun (also using the Scribner). I wish I had scaled all the short logs separately and compared that figure to the long log scale. If you sell long logs to the big mills, you get a much better price/bf than if you sell short logs.

There is an assumption about taper in every log rule.

It is a small, picky item, but usually overrun is called 100% when you have the same board footage lumber produced as the logs were scaled at. If you have twice as much lumber as the log scale, then the overrun is 200%. This understanding may help when you read some publications that discuss overrun. (In other words, 25% overrun is terrible as it means that you only got 25% of the footage that the log scaled!)

Gene Wengert, forum technical advisor


From contributor M:
What I mean about my hemlock job is that I am approaching 200% overrun, or double what the Scribner told me I would get. In short lengths, I get around 125%, unless I'm cutting beams or other large lumber, then it's closer to 150%.

Math trick: Instead of dividing the diameter by 1.3, multiply by 3/4 (three quarters). It's easier on the brain and close enough for the government.

W3/4 is not bad, but basic math says that any given circle will contain a precise .699 square area. Let's round to 70% so a 14" small end log yields a 9 3/4" X 9 3/4"cant. If the log length is 12', the International scale gives us a tally of 100 bft. But we all know that the extra butter lays with the minimum possible of our 4 second cut boards another 4x+-8"x12'=32bdf of course we must weep a little for our thin kerf sawdust. Now if that log has a generous taper, back to your black ink pen! The point I'm trying to make is that, historically, the loggers were always the suckers to the big mill industry in Canada, the
US, any country with a standing tree no matter what scale you are using.

From contributor A:
Fair is fair. But the scales are a bit tilted. But when you figure in the bad logs and time spent it must even out.

When I log and buy Southern yellow pine I try to get them 25 ft long and I cut them down to 8's, 12's and 16's and sometimes I saw them as 24's. I add 2 inches to the measure and 30% to the ticket for long logs. I saw from the butt and get every board in there. Last load I paid for 1560 bdft (that's with added) and sawed out a tad over 3000 bdft. Next load I will add 40% because fair is fair.


But here in the West, the bad logs one might sell are docked according to the defect; butt swell, conk, sap-ring, knot size, sway, spike knots, etc. No pay is given for the fiber that is gained in these instances, nor is any type of credit. The big boys win again. The big industry has established the standards by which it regulates itself. Log grading, lumber grading standards, etc., whether on the international, national, regional or local level. If the little guy was so organized we might even begin to set our own standards and fall prey to the same sort of issues we are talking about here.

I have not seen the article in Tree Farmer but I assume it is about complaints from woodland owners who believe they are being cheated by the scale overruns. I have heard these complaints before but I don't believe they are valid as long as the woodland owners get bids on the stumpage and then it makes no difference what scale you use. Each bidder should look at the quality of the trees and use their own estimates as to what he can pay for that stumpage, the scale used is just part of the mechanics of bidding and should not affect the outcome.

If the woodland owner still thinks they are being cheated by the "scale" they can always go out and buy all the equipment, pay for the insurance, and then be able to tell the stories about "the tree that almost got me".


When all is said and done, whether in the West or ??, the landowner will get so much money for the wood, no matter what scaling method is used. The money will be the same.

If any timber owner thinks he is being ripped off, that will not change based on the scaling system used. If an accurate scale were used, then there would be lower prices paid per BF, but the load would sell for the same money. Plus, since smaller logs require more cost to produce lumber, the accurate scale would have a sliding price scale to cover the added costs for smaller logs. I think that right now, scaling covers these extra handling costs but underestimating with small diameters.

Gene Wengert, forum technical advisor


My dad cut and sold white oak barrel stave bolts for years. That was back before they bought the logs when bolts were cut to some length and split into 1/4s, 1/3s, or 1/2s. He would take his load to the stave mill where the buyer would come out and start the process of haggling over the price per foot based on quality, size and demands, etc.

Once the price per foot (measured across the corners of the little end of the stave) was established, the measuring began. The buyer ran a 100' cloth measuring tape and dad would mark them off as they were being measured. The first stave was measured and then the tape pulled to accumulate the width of the next and so on.

If the buyer thought he had to bid too high on the price per foot, he'd make up for it by "measuring his thumbs" - this is, you'd get shorted the width of his thumbs each time he advanced the tape to measure the next bolt. Other tricks they used were to just "snap" the tape and not advance it at all. In extreme cases, they would actually pull the tape in the other direction now and then to reduce the total footage. Another trick was to take a new tape and soak it in water, stretch it and let it dry. It would be about 110 feet long. After time, it would shorten again to at or less than 100'. Every time the buyer came out with a new tape, Dad knew he was going to have a light load.

Dad is the most honest man I've ever known and never tried to "put one over" on the buyer by bringing in junk they couldn't use. Got to the point where he would pull into the lot and the buyer would ask him how many feet he had on (Dad always measured before he took them to market) and what he thought they were worth. If they agreed, he'd send him on to unload while he had the check made out. If the buyer wasn't busy, he'd go through the whole song and dance mostly just to visit.

In the end, the buyer paid what he wanted to for the product.


Formula for overrun or underrun:

% overrun = (lumber yield/log scale) - 1 * 100

0% would be lumber yield equal to log scale.

100% overrun would be double the log scale.

Source: the Forestry Handbook


Thanks for the detail of overrun. That's how I have always figured it. If a log scales 100ft and I cut 200 bd ft of lumber I figure it to be 100% overrun.

I live in Oregon and we use Scribner scale.

As for overrun, when I am cutting dimension lumber out of Douglas fir, I count on getting at least 35% overrun on short logs.

If logs are scaled long (in this area a common length for a long log is 42 ft--his is the length most of the big mills want), I will get from 100 to 200% overrun.

The job I am just finishing is Douglas fir logs 20, 16, 12, 10 and 8 ft. The diameter is no more than 16 in in the 20 ft logs and many of the others are as small as 6 in. I am getting over 100% overrun.

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