# 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.

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