Board Foot Measure (BFM)

We had a windstorm recently … some big trees down. After cutting up most of the fallen ones on my property (taking a couple weeks), I started in on one of my neighbor’s. One of `em is a big oak. There’s are two straight sections that could be, theoretically, cut into boards. I have a chainsaw mill. It’s awesome, but, heavy, a lot of work. It would be easier to just cut all of the tree (and big branches) … into firewood. But my wife’s face lit up with the prospect of countertops!

“I don’t do countertops.”

I tasked her with finding out how thick countertops are, and how many square feet she needs. I handed her a tape measure. “Tell me how many `square feet’ you need.” Then I headed outside to measure the tree.

I’d rather not fuss with the chainsaw mill, but her birthday is coming up.

A bit later she said, “35.68 square feet.” I said, ”whoa, nice!” (I saw that she started with measuring the counters in `inches’.) “ … I divided by 12 and came up with 404.16. But I knew that wasn’t right; a tiny house is 400 square feet. So then I divided by 12 again, and got 35.68.” “Good job!”

… when I was teaching, I would make my students do a “does the answer make sense?” check. “Good job!” She checked her answer by something she knew. Awesome. I would have just walked up next to the counter, paced off 15 or so feet, and multiplied by the width, 2-ish feet … 32 square feet.

… (but) 404 square feet of countertop would be absurd (in our kitchen) … I’d chastise my student hard for an answer like that.

“How thick?” She said … `5/4’. “One layer or two?” … `One’.

Okay, 5/4, as I remember, stands for 5 fourths of an inch. Oh, and it’s a `nominal’ dimension. (Nominal means, `in name’.) So, it’s not actually 5/4ths of an inch thick, but a bit less. For now, let’s say an inch, `actual’, or maybe 1-1/8 inches. The actual volume of wood that she needs is … 36 square feet times 1.125 inches, or 405 square feet-inches. But that’s a weird number (and, presumably only a coincidence nearly equal 404) … let’s divide by 12 (inches per foot): 405 square feet-inches / 12 inches per foot equals … 3.375 cubic feet … let’s say 4 cubic feet of wood.

Now let’s look at the log. The segment I want to use is 7 feet long, and diameter about 16 inches. When I take my mill to the log, I’ll be cutting off some of the `round’, so, let’s consider a square section that `fits’ inside a 16-inch diameter round (circle). (I’ll let you prove that the sides of the square, that just fits, are 1/√2 times the diameter … or 0.707 times 16 equals 11 inches. The square section has an area of 11 times 11 or 121 square inches, or 121 divided by 144 gives 0.86 square feet. The volume of (supposedly) available wood is 0.86 times 7 or 6 cubic feet. Six available versus four needed …

It looks like I’ll have enough wood, BUT, a couple things: first, the chainsaw (mill) turns a significant amount of wood into sawdust, and, second, having done this before, but for flooring, it seems I always end up milling way more wood than I thought I needed. We’ll see. In the mean time, I’m glad she didn’t say `2 inches’ … (thickness).

Board Foot Measure

If for some reason I don’t succeed at cutting up my neighbor’s tree for countertop, Linda has been looking into materials herself. Passing by the YouTube video she was watching, I heard something about 5/4, and `Board Feet’. Board Feet! … or Board Foot Measure! … I love it! (BF, BFM!) Lumber is often measured in `board feet’. I didn’t know that countertops are measured such, but, again, I don’t do countertops. Let’s calculate what she will need for countertop materiel, in board feet.

Board Foot Measure utilizes `nominal’ dimensions.

How many feet, `board feet’, or material will she need?

Linda measured 4850 square inches of countertop needed. I went over and measured 25-or-so inches wide. So, assuming she also used (about 25), she must have measured about 4850 / 25 or 1294 inches, or … 16 feet. Seems about right.

Then to the NDS `Supp’ (National Design Specification® for Wood Construction, Supplement – Design Values for Wood Construction). Table 1A provides sizes of boards. Boards are available in nominal sizes from 1 x 2 up to 1-1/2 by 16. Since nothing is 25 inches wide, let’s consider two pieces of, say, 1-1/4 x 14 (or maybe 16). These are `nominal’ sizes … nominal means `in name’. So, a 1-1/4 x 14 is not actually 1-1/4 inches by 14 inches. The Table also provides `Minimum Dressed’ dimensions. For the 1-1/4 x 14 it shows … 1 (dry) and 1-1/32 (green) by 13-1/4 (dry) and 13-1/2 (green) (inches). (This reminds me … the tree was living just a few weeks ago, thus `green’. After milling, I will need to let dry for a while, before installing. I hope she’s not in too much of a hurry for those counters.)

So, two pieces side-by-side (dry) is … 2 x 13.25 or 26.5 inches … should be good.

So, she could ask for 2 pieces of 1-1/4 by 14 x 16 feet long.

How many `board feet’ … if she’s asked.

“How many board feet of 1 x 16?”

Board foot measure … here’s how I remember: a one-foot-long 1 x 12 is ONE board foot.

We could say … board foot measure, BF, or BFM, is thickness (in inches) x width (inches) x length (feet), divided by 12.

BF = b x d x L / 12.

A 16-foot piece of 1 x 14 is … 1 x 14 x 16 / 12 = 18.67 board foot of 1 x 14 lumber.

Two pieces is 37.3 BF (of 1 x 14).

But before she marches off to the building supply store … these are countertops, and there is a corner, and there is cutting around the sink, and stove, etc. There’s going to be some waste, trim. Let’s say 15% … and by that I actually mean, `let’s order 15% extra, since there will be some waste’.

So, 37.3 + 0.15 x 37.3 = 42.9 … say 43 BF.

If, we use 1-1/4 x 16 instead … 43 BF x 16/14 = 49 BF. (I’ll let you check my math.)

Some more on BF, or BFM.

How may board feet are in a cubic foot of lumber?

One BF is 1 x 12 x 1 foot long … (one square foot x 1 inch thick).

If it’s 12 inches thick (one foot) instead of 1 inch thick … then it’s 1 x 12 BF.

We could say that BF measure is `cubic foot measure’ … multiplied by 12.

Or volume measure (in cubic inches) … divided by 144.


BF repeated (reworded)

… to understand (or remember) `board feet’, think of a `board’, that is, say, 12 inches wide, and however many feet long. One board foot is a one-foot length of one-inch-thick board, twelve inches wide. If you have a board that is 2 inches thick, and 12 inches wide, and one foot long, it is … 2 board feet. More often, our boards are more than one foot long. Say the 1 x 12 is 2 feet long. It is 1 board foot per foot, so 2 feet will be 1 board foot per foot, times 2 feet, or 2 board feet (2 BF, or 2 BFM).

A 2 x 6 board, even though only half as wide, is twice as thick, giving us the same as 1 x 12. So a 2 x 6 is 1 BF per foot. A 2 x 12 (that is) 1 foot long is 2 BFM. A 2 x 12 that is 10 feet long is a total of …. 20 BFM.

If you want a formula … BF, or BFM = (b x h) / 12 … x L, where b is the thickness, in inches, h is the width, in inches, and L is the length, in feet.

So, an 8-foot long 6 x 6 is … [ ( 6 x 6 ) / 12 ] x 8 = 24 BF.

Maybe we could cast the formula as,

BF or BFM = [ ( b h L ) / 12 ] BF / in.2-ft.

Let’s try it … 1 x 12 x 4 feet long … 48 in.2 ft / 12 x BF / in.2-ft … or 4 BF.

… I’m making it too complicated. Just remember …

1 board foot is … 1 inch thick, by 12 inches wide, by one foot long, … and go with multiples (or fractions) from there.

And don’t forget … Board Foot is based on nominal dimensions.

KEY WORDS: nominal, dimension, dimensional, nominal dimension, BF, BFM, board foot, board feet, board foot measure, lumber, wood