Board Feet Calculation Dilemna

[Joe D'Attilio]

I have tried 6 different sites/BF calulators and all 6 gave me different results...

Can someone expalin calculating board feet

I want to make a workbench top out of maple or even yellow pine and would like to estimate cost.

I figured I would use (10) boards 2" W x 60 L x 2" Thick = 20 X 60 Top (not including aprons)

Using a std formula... I come up with:

(L X W X H) / 144 (X qty of boards)
(60" X 2" X 2") = 240
240/144 = 1.667
1.667 X 10 = 16.67

Add in 30-35% for waste
1.35 X 16.67= 22.5 or 23 BF

Is this correct? and can someone post the link for a good BF calculator?

[Sam Yerardi]

Joe,

One board foot is the AMOUNT of wood in 1" x 12" x 12". Your formula is correct but you need to keep in mind the dimensions of the wood you need. In other words, your calculation may show that you need 10 bd ft, but the calculation doesn't show that maybe one of the boards you need is 9" x 3/4" x 60". 10 bd ft can show up in many different dimensional configurations and still be the correct AMOUNT of wood you need, but not in the dimensions you need.

[Peter Quadarella]

A board foot is a 1 foot x 1 foot board, 1 inch thick. If you want to convert to cubic inches, you can multiply your dimensions, so 1 board foot = 12x12x1 = 144 cubic inches.

If you want a 20 x 60 top, 2 inches thick, then you need 20x60x2=2400 cubic inches, which is 2400/144=~16.6 board feet.

So yes, looks correct to me. :)

[Joe D'Attilio]

This is just for the top of the bench.

I plan to join 10 pieces against the faces together

10 @ 60" X 2" X 2"

Making the overall dimensions of the top:

60" X 20" x 2".

Is my calulation of 23 BF correct for 10 pieces "if it was a perfect world" or I bought them cut to dimension?

Meaning 23 BF x $3.50 for roughly - $80 based on these calulations?

[Chris Padilla]

It is more common to measure the thickness and width in inches and the length in feet. Going by that, I get:

(2" * 2" * 5')/12 = 1.67 bf

There is nothing wrong with your calculation.

The thing to remember is that board feet (bf) is a VOLUME measurement with the somewhat crazy units of ft^2-in or in words: feet squared inch or inch-feet squared (in-ft^2) if that sounds better to your ears.

Really, of the 3 dimensions of rough lumber to measure to get the board foot number (a volume number), 2 of them should be in feet and the other in inches. That way you don't have to divide by anything to convert inches into feet.

So if everything is in inches, you divide by 144.

If two dimensions are in inches (and the third in feet), you divide by 12.

If 1 dimension is in inches and the other two in feet, no division is necessary.

I hope this helps.

[Chris Padilla]

This is just for the top of the bench.

I plan to join 10 pieces against the faces together

10 @ 60" X 2" X 2"

Making the overall dimensions of the top:

60" X 20" x 2".

Is my calulation of 23 BF correct for 10 pieces "if it was a perfect world" or I bought them cut to dimension?

Meaning 23 BF x $3.50 for roughly - $80 based on these calulations?

Also, know this is for ROUGH wood. If you buy 1 bf of wood that is 1" thick by 1 foot by 1 foot, you will get a thickness LESS than 1" most likely...if you buy S2S or S4S. If you buy rough, you should get an inch thick and then you plane it down until smooth.

[Joe D'Attilio]

Math wasn't always my strong - but I could always measure and figure out what i needed when it came to wood...

Just so confusing and you start 2nd guessing yourself when 6 different sites tell you 6 diff results...


Thanks Everyone

[Mike K Wenzloff]

Hi Joe,

Your math is correct, just more involved than it needs to be on a solid single piece like a top.

However, I seriously doubt if you actually bought lumber milled to those dimensions your finished top would equal the desired 2" x 20" x 60" dimensions.

I don't mean to sound pedantic. Accounting for waste is one thing. But you will need to buy lumber longer than 60". You will need to buy lumber thicker/wider than 2" and resaw and/or rip. That is even if you are ordering the lumber you plan on using milled to your spec.

Will 1/3 wastage be enough to account for the processes? In part it depends on what the processes you will use in order to end up with the final desired dimension. Also depends on the species of wood.

I assume you will need to flatten both sides following glue-up. You will need to trim to final length--the ends will most likely not be perfectly even following glue-up. Depending on how precise the long sides need to be parallel to each other, you may need to plane or rip the width.

1/3 wastage can be eaten up fairly fast just in over length, over width, over thickness issues if you are milling them yourself. That's not to mention boards that may become wonky or have undesired defect during working on them.

But if you buy the wood pre-milled, you also need to over-spec it if the final dimensions are an absolute requirement.

Take care, Mike

[Denis Tranchemontagne]

I've been trying to work this out too, as I would like to build a workbench in the near future. The best I could figure, using 2" rough wood, I would need 14 boards assuming 1.75 inches thick after milling.

Considering my bench top would be 3"X24"x6ft = 36 bft. however I would need 14 boards to make this thickeness not 12. 24/1.75 ~= 14
Having gone to the lumber yard (not purchased anything yet). The typical board I could get would be 2''x8"x8ft ~10.7 bdft lets make the math easy, say 10bdf @3.00 /bdf = $30 a board, 7 of these would be $210. This is almost 100% waste (boo hiss).

Obivously If I could find 7fters and 7 inch boards I could do better (less waste) also getting longer boards to cut the legs from (say 10fters) I could minimize waste.

This does seem like a lot of waste. Could one use the scraps end to end to make a long board, if so how should they be joined.

Denis

[Sam Yerardi]

You can use scraps end to end. There are some bench top designs where the boards are laid out such that you create dog holes in the process, i.e., a space of 5/8-3/4" between each end, etc. so yes, you can join end to end, but I would do it only with solid continuous boards on either side.

I've also seen designs where the top was through-bolted, biscuits used, dowels, so there are several different methods. I think the key factor is what will you expect the wood to do as far as movement - I remember reading an article in Fine Woodworking where an author of an article indicated he once used through bolting with threaed rod. The only problem was in his case that the wood had other ideas about movement and the rod ended up creating further damage that wasn't repairable once the wood began moving. His was an isolated case as he was making a point about using non-dried material.

You can typically distinguish SYP from all of the other pines, firs, spruces, etc. by the look of the face grain.

[Chris Padilla]

All I can say is keep an eye out for deals on wood...they CAN be had.

For example, I found a guy selling 18" x 36" maple butcher blocks. I *think* they are an inch thick. That is 4.5 bf per block. I forget what I paid but I think I picked up 12 of them for $200. That is about $3.75 bf for maple butcher block...not a bad deal at all out here in California. I recently paid $4/bf for rough 10/4 maple, 10' long, 8-12" wide.