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2Chessies
Posts: 776
Registered: ‎10-26-2009
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calculating board feet in a tree trunk

I know there is a formula to accomplish this but I don't remember where I seen it posted at.Does anyone know what it is. I know how to do it once a tree is cut into boards,but do not know how to estimate it otherwise.

We had to have 3 trees cut down from one of my job sites and I was able to work out a deal with a local sawyer to cut 1/2 of an ash tree and 1/2 of a maple into boards for me in exchange for the remaing wood. He will end up with an ash tree that is approximately 26" thick and 12' long,1/2 of a maple that is 32" thick and 11' long and 1/2 of an ash that is 24" thick and 12' with a crotch left intact. My portion of this wood will be 1/2 of one ash and 1/2 of the maple. I don't know how to calculate it out to board feet before cutting so I can decide what thicknesses I would like to have it in.

Honored Advisor
stick48668
Posts: 11,089
Registered: ‎01-15-2010
0

Re: calculating board feet in a tree trunk

here ya go...

 

http://www.woodweb.com/Resources/RSCalculators.html

 

    1. Measure the height of the tree you are studying.
    2. Measure the diameter of the tree you are studying. Make sure you write these two measurements down very carefully on the data sheet.
    3. Remember the formula to find the area of a circle is (A=r2 x p). Area = radius squared times 3.14). Since a tree is almost circular, use this formula to find the area of your tree at DBH (diameter at breast height). Since the formula requires the radius of the tree and you just measured the diameter, divide the diameter by 2. Dividing the radius by 12 converts inches to feet.
    4. Now use this number to calculate the area of your tree.
    5. Don't relax now! We are only beginning! Use the formula in step 5 of the data sheet to find out how many cubic feet of lumber are in your tree.

       

      Cubic Feet = Area (ft) X Height (ft) / 4
      (note: 4 is used to account for the taper of the tree)

There are 12 board feet of lumber for every one cubic foot, so multiply cubic feet by 12. You have calculated how many board feet of lumber your tree has.

 

or....

 

  1. Height _____ feet
  2. Diameter _____ inches
  3. Diameter in feet / 2 = ________ radius in inches / 12 = _____ feet
  4. Area of tree cross-section = above number squared x 3.14 =______ sq.ft.
  5. Volume of tree in cubic feet = above number x tree height / 4 = ______
  6. Volume of tree in board feet = above number x 12 = _________


this would have been the week that I'd have finished chewing thru the restraints...
if only new layers hadn't been added....

Stick....
Veteran Advisor
Sawdustr
Posts: 8,323
Registered: ‎10-21-2009
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Re: calculating board feet in a tree trunk

Good Morning Chessie,

Stick is right on target with his post, however those of us who may not have had a computer in days gone by here is another method you could use.

 

If the log measures 16' long and 24" in diameter on the small end. You deduct one inch from all four sides to remove the bark and that leaves a square log of 20", now square it by dividing it by 4 and you get 5² or 25 x the 16' of length and it will produce approximately 400 board feet.

Remember to keep your hands no closer to a spinning blade or bit than 6" for safety sake.

Respectfully,

Ralph Jones General Forums Host

http://www.ralphjoneswoodworking.com
Veteran Advisor
brianalt
Posts: 1,331
Registered: ‎04-15-2010
0

Re: calculating board feet in a tree trunk

Stick, are you sure your equation is correct? I tried a sample calculation with a 24" diameter tree 16' long and I get 400 board feet with Ralph's method and with the calculator on the link you supplied. But with your method I get 150. I suspect that dividing by 4 to account for taper is too high. 1.5 instead of 4 works out better.

Honored Advisor
stick48668
Posts: 11,089
Registered: ‎01-15-2010
0

Re: calculating board feet in a tree trunk

dividing by 4 accounts for taper and bark..



this would have been the week that I'd have finished chewing thru the restraints...
if only new layers hadn't been added....

Stick....
Veteran Contributor
jsbduncum
Posts: 119
Registered: ‎12-30-2009
0

Re: calculating board feet in a tree trunk

Stick, I have to agree with Brian. My math came out to about 150 also. It peaked my curiosity so I drew a 20" diameter circle and layed out 1" cuts and a 16' log would be about 400 bdft. What are we doing wrong? JD
Honored Advisor
stick48668
Posts: 11,089
Registered: ‎01-15-2010
0

Re: calculating board feet in a tree trunk

try the Doyle scale...

it says 280 for IRL BF count...

 


 

 

.This is the actual formula for calculating Doyle scale...



this would have been the week that I'd have finished chewing thru the restraints...
if only new layers hadn't been added....

Stick....
Honored Advisor
stick48668
Posts: 11,089
Registered: ‎01-15-2010
0

Re: calculating board feet in a tree trunk


jsbduncum wrote:
Stick, I have to agree with Brian. My math came out to about 150 also. It peaked my curiosity so I drew a 20" diameter circle and layed out 1" cuts and a 16' log would be about 400 bdft. What are we doing wrong? JD

flat sawn a 20"x16' log will produce that much...

and serious pile of waste...

Warping and twisting will be out of control..

 

IRL you are only going to get between 150 to 280 BF of quality timber/wood/boards...

 

Some place in this forum is a picture of a log, the cuts done to it their location within the log and what happens to product...

 

 

Gonna go look for it .

 

 

 



this would have been the week that I'd have finished chewing thru the restraints...
if only new layers hadn't been added....

Stick....
Honored Advisor
stick48668
Posts: 11,089
Registered: ‎01-15-2010
0

Re: calculating board feet in a tree trunk

see where I was going with this???

 

shrinkage wood movement.jpg



this would have been the week that I'd have finished chewing thru the restraints...
if only new layers hadn't been added....

Stick....
Veteran Advisor
brianalt
Posts: 1,331
Registered: ‎04-15-2010
0

Re: calculating board feet in a tree trunk

The Doyle's equation you posted above is exactly the method Ralph used to calculate board feet: take the diameter (in inches), subtract 4", divide by 4 and then square it, finally multiply by the length to get board feet.

 

  ([24-4]/4)² x 16 = 400

 

Are you trying to estimate usable board footage?

 

Brian

 

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