Spanish Clearing up the confusion about lumber quantities and unit conversions. April 14, 2005

Question

I was trying to calculate the board feet of lumber for a wall, length 10' x height 10'. If I use a 2 x 6 lumber size, what will be the total board feet required for the wall? And is there any easy way of converting a square feet to board feet? And do estimators usually consider windows when calculating the BF of lumber for a wall?

Forum Responses

(WOODnetWORK Forum)
*From contributor A:*

For 2 x 6 stock, a board foot = a lineal foot, making the calculations a bit easier.

To go 10' wide, you will need 20 boards. Each board will also be 10' long. So, unless I'm asleep at the wheel, the answer to "how many board feet of 2" thick material to cover a 10' x 10' wall" would be something like 20 x 10 = 200 BF.

Don't forget to figure in for an appropriate scrap factor.

So, if I use 1 x 6 lumber size, I will need only 100 BF? To be clear, for a 2" thick material to cover a 10' x 10' wall would be 20 (no. of boards) multiplied by 10 {2" (width) x 6" (thickness) x 10' (length)/12}. Is this how it works? And are these boards called as plates in construction terminology?

Unfortunately a 1 x 6 board is not 1" x 6". In reality it is 3/4" x 5-1/2". As such, you can't just take the width of the wall and divide it by 6". Instead you have to divide it by 5-1/2".

So, a 120" (10') wall will require 22 boards rather than 20 - plus typically about 15% for waste unless you get nice clean 10' long boards for your 10' ceiling and there are no doors or windows to trim around.

thickness x width x length % 144

IE: 1" thick x 12" wide x 12" long

% 144 = 1 Board foot.

144 square inches = 1 BF.

To contributor C: Your formula equals one square foot, not one board foot.

A 1 x 12 board is typically 3/4" x 11-1/2", yet one running foot of it is referred to as "one board foot". However, as you can see it is not a full square foot.

To contributor B: Sorry, you are wrong. Get out your pen and paper, multiply 1 x 12 x 12 and divide this by 144 and then tell me what you get. A board foot is a measurement used for rough sawn lumber. A 3/4" board in the rough is 1".

One other thing - if you want you could measure it like this, .75 x 11.5 x whatever your length, in inches, and then divide this by 144.

To contributor C: Okay, .75" x 11.5" x 120" (a 10 foot long board) divided by 144 equals 7.1875. I'm not sure just what you want this to show me though.

Let's go back to the original post asking how much lumber should be purchased. We can simplify it by saying 1 x 6 is needed rather than 2 x 6.

The 10' x 10' wall is 100 square feet. It would seem that by what you are implying 100 board feed of 1 x 6 is needed. However as you know 1 x 6 at a lumber yard is actually 3/4" x 5-1/2" (the thickness really isn't an issue here though). If just 100 board feet of 5-1/2" wide 1 x 6 in 10' lengths were purchased there wouldn't be enough material to reach the other end of the wall. All the boards would reach the ceiling (assuming vertical placement) but 120" divided by 5-1/2" requires 22 boards whereas 120" divided by 6" requires 20 boards. All this is assuming we are talking square edge material here rather than tongue and groove, which would further increase the number of boards required.

My understanding (and I've been at this over 30 years so if I've been wrong I'd like to know now) is that board feet is a tenuous description of an amount of lumber. In the rough it is, as you say, an accurate description of the amount of material in a given board.

However, as soon as the board is planed and ripped to its retail size it no longer contains that much material. If you go to the lumber yard and order a 10' length of 1 x 12 it will be billed out as 10 board feet even though it’s only 7.1875 square feet of 3/4" thick material.

I should add that I was in error when I originally stated your formula equaled 1 square foot rather than one board foot. What I should have said was that it equaled 1 square foot of 1" thick material. I can see that leaving that out led to some confusion in the discussion.

When I'm training a new person, I beat into them the idea that the board foot is a measurement of volume, not area. This helps them with the thickness calculation. I think the confusion in this thread comes from the way S4S lumber is measured and sold. Generally in my experience S4S is sold by the lineal foot rather than the board foot. If this is the case, then contributor B is correct - one should calculate based on actual size rather than nominal. To the original questioner: Order heavy. The worst thing that can happen is that you are a board short, the job sits, and the dealer has a $300 minimum.

I think contributor D came close to explaining the confusion, but I'd have to add a few notes. I think both contributor C and contributor B are not understanding what each is trying to say, yet both unknowingly agree. A board foot is a board foot. It is not a square foot. Now, let’s look at the term's application: contributor D says a lumber yard typically sells S4S in linear ft. Yes, Home Depot, Lowes etc., do sell oak, poplar, ash etc. by the linear foot. This wood is S4S. Where most woodworkers, not framers or builders buy our lumber, it is sold by the BF and is usually not S4S, but probably S2S and ripped straight one side. While this lumber is sold by the BF, it is usually true that you are paying 1" thick price for a 3/4" board. This is common practice. However, the way I look at it, you are paying for a 1' board that has been planed down to 3/4" (actually 13/16' to 7/8"). So, yes, you can definitely say that you're not actually getting a real BF when the thickness factor is calculated as 1" at check out. This is absolutely true. I believe this is a generally accepted practice with S2S lumber that most of us realize. On the other hand, if I'm buying rough, say zebra wood, if it's 3/4" thick I'd expect the BF will be calculated using 3/4", not 1", as the thickness.

Does this clarify anything? I hope I explained it so that you each see that you're really not at odds with the definition of a BF, but only with the sometimes real world application of the term.

A board foot is a measurement of rough cut lumber. Thickness x width x length in inches divided by 144. If you buy a surfaced board, you are still buying the rough board but you are getting the services of surfacing.

Let’s start at the beginning. The original questioner is trying to calculate the board foot of lumber needed to build a wall, not the lineal foot. I know, he should be calculating by the latter, however that wasn't his question. To properly calculate a board foot you multiply thickness x width x length then divide this by 144. No matter how you slice it, there are 144 square inches in one board foot.

Let’s go back to what I had asked contributor B to calculate, .75 x 11.5 x 120 divided by 144 = 7.1875. This is how many board feet are in a retail 1 x 12 x 10', however it is considered to be in most cases 12 lineal feet. The only time that it was 12 board feet was before it was milled to dimension. I don’t know of any retail lumber yards, at least here in the Northeast, that are selling lumber by the board foot. Let me clear one thing up - I never suggested that 3/4 of an inch be calculated as 1".

So, I will leave it at this, there are 144 square inches in one board foot.

To contributor C: My major error was in definitively stating that you were describing a square foot rather than a board foot. What I should have said was that from my perspective on things you were describing a board foot only in the rough. With regard to the original question, that would be seen as a square foot.

Certainly a rough board at 12" x 12" x 1" is one board foot and I should have acknowledged that. If you need to cover a square footage area with milled lumber though, you have to add in extra board footage.

Granted most retail lumber yards will sell pine etc. by the lineal foot. Flooring however, is regularly sold by the board foot and one has to calculate how many additional board feet will be need to cover a given square foot area. As such, even though technically one board foot is 12" x 12" x 1", in the real world the term is given a wider use.

I wanted to say something like one board foot always equals one square foot, but not vice versa. However, this has already gone a bit too far to bring in yet another quite arguable absolute.

To contributor B: I'm glad you didn't say 1 BF always equals 1 SF, but not vice versa. Contributor F summed up in two sentences what it took me a paragraph to explain.

Well - many ways to figure BF. Where I am, on blue prints most Architects spec the way you say, however 1 x 4 is really 3/4 x 3-1/2 if they want a full 1" thick I find that most of the time they will call out 5/4 and than you know it is a full 1" thick.

To contributor C: Is this what you mean?

How many board ft in a cubic foot?

12 x 12 x 12 = 1728 ~ 144 = 12BF.

1 x 12 x 12' = 12 BF , 1 x 6 x12= 6BF.

An easy way to figure BF in a 12' board – it’s always the same as the width times the thickness of material.

I also thought that the original questioner was trying to cover the wall with a paneling of wood as it would take 100 SF exactly or 100 BF exactly.

To contributor B: I agree 100% with your description, very good details.

When buying flooring you buy it by the SF, not BF- and when buying flooring they are talking about the amount of coverage you are getting not how many board ft. it took to make the SF you are covering.

I goofed on the wall paneling - it should have read 200BF as he did say 2 x 6.

If an architect called for 5/4 I would have to assume 5/4; when an architect calls for 1 x then he is going to get dimensioned lumber. Most of the architects I have experience with have used decimals anyway so you can't interpret it wrongly.

1. A board foot is an exact measurement of volume. This is as basic to woodworking as the difference between a ripping blade and a crosscutting blade.

2. Architects are, more often than not, designers with college degrees. It's my firm opinion that no architect should be issued a pencil until he's done a 2-year apprenticeship out in the real world of construction, carrying materials, installing sinks and grouting tile.

3. The original poster needs to calculate his material needs based on square feet, not board feet, and that based on actual physical dimensions of the material he will be using, i.e. 5-1/2" x 10' long.

To the original questioner: Your wall is 10' x 10', 100 square feet. It doesn't matter how thick the material is that you are using, you still need 100 square feet of material. If you're using dimensioned 2 x 6 material, it's 5-1/2" wide. If you buy 10'-long material, you just divide 5-1/2" into 10', or 120". This yields 22 pieces. If you hand pick them, that should be all you need, and you will have some fall downs from cutting around your window. Adjust as you see fit.

You really should work with this stuff until you feel comfortable with square feet and board feet and related subjects. It's really basic to what we do, and if you don't know this, how can you know you're not getting shorted by your supplier or that you're buying the amount you actually need?

How do you know he's not covering a barn wall with rough cut? Then it would work using BF to get SF 200 BF divided by 2 = 100 SF

You're right, I don't know that. Well, now either way someone has done his homework for him.

When I check in a pack of 1000' from the lumber yard I measure the length X width X how many courses (4/4) and divide all that by 12.Anything thicker than 4/4, like say 5/4, I would then X everything by 1.25.

I must say if I have a wall to panel I ask for the square footage I need with the waste factor figured in. They give me a price based on the board footage they will need to make what I want and were all happy.

To contributor H: If I sell you 1000 BF rough lumber by a true lumber scale, and you stack it all in a pile let’s say 4' wide x 10' long that would = 40 BF per layer or 25 layers high, to give you a true 1000 BF. However, by true scale in hardwood anything that is, let’s say 5-1/2" wide, is called out as 6" in true scale and so on, so I am sure that when you do a tally this way you must think that you are short as I am guessing that you only get around 23 layers of lumber or only around 920 BF. Or maybe they ship you more than you asked for.

In a pack of lumber we get in, all of the boards are random width. But the pack is usually around 42" wide. I do this as a box tally and compare it to their board tally on the invoice and usually it comes up close. If it is off a lot I call and complain. There have been a few times they ship too much. I let them know that too. Always a sales rep shows up to verify things. Most of the time, everything matches up.

If you get really picky there’s air space between the boards. There are so many different people who do different things in this industry. It's got to be hard to convince anyone of anything because they just know what they were taught, including me. But, if you’re in the guidelines and make a living, I guess we’re all doing something right. My tallies work with the distributors that send them to us so I know we’re on the same page there. I guess that’s what matters.

When buying random width lumber, anything 1/2" over is rounded up but anything below that is supposed to be rounded down, so I can get along with that. What I don't like is the 7% shrink charge, 14% if you get straight line rip. I don't care if it is measured green and they lose out if they don't add the shrink charge, they should add that to the price. Some add it to the total tally and some add it to each board, when added to each board you can really lose out. One time I bought a small amount of alder to try out and two of the boards were 1" x 4" x 72" which equals 2 board feet each. The paper showed 3 BF each for them, and the total I was charged for was 127 BF - and I got about 93 BF. All of these boards were narrow and rounding up and shrink charge caused this. I complained and they made it right but I still don't like shrink charge.

I would recommend reading the Knowledge Base articles (listed below) for starters. There is quite a bit of information on this topic in the WOODWEB Knowledge Base, and much of it has benefited from Professor Gene Wengert's input. There are well established and accepted methods for calculating board feet, and woodworkers should review this information so that they are aware of the accepted way to calculate board footage.

There is also a board footage calculator at WOODWEB, which can be found at:

Board Footage Calculator

I would encourage all those who are trying to understand how to calculate board footage to review these resources.

*Comment from contributor J:*

From contributor C:

Thickness x width x length / 144

IE: 1" thick x 12" wide x 12" long

144 cubic inches = 1 board foot.

144 cubic in = 1 BF.

Yes contributor C is correct except there is a technical typo. We all know what he meant though. 144 cubic inches = 1 board foot not square inches.

So it is extremely important to use your symbols and exponents such as squared or cubed in³.