Board Feet Is the Easy Part

Thickness times width times length, divided by 144. Anyone can do that. What sends people home from the lumber yard with the wrong amount of wood is everything around it.

Ask a woodworker how to calculate board feet and they’ll tell you correctly: thickness in inches, times width in inches, times length in inches, divided by 144. It’s arithmetic. The reason people still end up buying too little wood — or, more expensively, far too much — isn’t that formula. It’s that the number you calculate from your drawing is not the number you should be buying. Using a board feet calculator properly means understanding two adjustments that sit between the finished piece and the pile of lumber you carry out of the yard.

You buy rough, you build finished

The first adjustment catches nearly every beginner and a fair number of people who’ve been doing this for years.

Your drawing specifies finished dimensions — a top that’s ¾ inch thick, legs that are 2¾ inches square. But rough lumber isn’t flat, isn’t square, and isn’t the thickness on the label. Getting it flat means removing material from both faces, and getting it square means losing some off the edges.

So a ¾-inch finished part comes out of 4/4 stock (nominally one inch), because that inch is what allows for flattening. A 2¾-inch leg needs 12/4 — or a glue-up from thinner stock, which is a different decision with its own arithmetic.

This matters two ways round. Calculate board feet from your finished sizes and you’ll under-buy, because you haven’t accounted for the material that becomes shavings. Calculate from rough sizes you’ve estimated yourself and you’ll usually over-buy, because you’ve double-counted the planing allowance.

The clean way is to work in finished sizes — the sizes you actually designed — and let the rough stock requirement follow from them mechanically. It’s a lookup, not a judgement call.

Thirty percent waste isn’t pessimism

The second adjustment is the one people argue about, and it’s usually the people who’ve bought too little who are arguing.

A waste allowance around thirty percent sounds enormous if you’re imagining a clean board and a careful cut. It looks entirely reasonable once you list what actually consumes lumber between the yard and the finished piece:

• Splits at the ends of boards, which have to be cut off
• Sapwood you don’t want in a walnut top
• Knots you’re designing around
• Cup and twist that come out as thickness during flattening
• Snipe at both ends from the planer
• Squaring the ends before you can measure anything
• And, eventually, the cut you make on the wrong line

That last one is the honest item, and it belongs on the list. Everyone does it. Building an allowance for it into your order is not defeatism; it’s the difference between finishing a project and driving back to the yard for one more board that turns out to be from a different tree.

The right percentage varies. A small project with wide parts needs more, because you have less room to work around defects. Figured stock you’re selecting carefully needs more again. Long, narrow parts from clean boards can need less. It should be a number you set, not one a tool imposes.

What you carry out of the yard

Put those two adjustments together and the useful output isn’t board feet in the finished piece — it’s board feet to buy, totalled by species.

In a worked example, a dining table with 23.7 board feet of finished parts requires 30.8 board feet purchased: 29.26 of walnut plus a little poplar for the parts nobody sees.

Two things about that.

It’s an order, not an estimate. You can hand it to somebody at a lumber yard. That’s a very different experience from arriving with a drawing and doing arithmetic in your head while somebody waits.

The secondary wood is in it. Using a cheaper species for drawer sides, backs and internal parts is traditional practice and it saves real money — but only if you remember to plan for it separately rather than pricing the whole project in walnut.

And a note on sheet goods: plywood isn’t sold in board feet and shouldn’t be forced into the same calculation. Track it by sheet, price it by sheet, and keep it out of your solid-lumber totals.

Then the three honest numbers

Once the lumber is costed and the project is finished, there are three ways to answer “what did that cost?” — and they tell you very different things.

Materials against retail. In the example, about $519 of materials against a comparable $2,400 table. This is the flattering number, and it’s the one woodworkers quote at parties.

Materials plus your time at a real shop rate. About $2,049. Which is a considerably less flattering answer, and an important one if you ever sell anything — because a piece that takes forty hours and sells for materials-plus-a-bit is a piece you paid to make.

Materials per hour of shop time. Around $15 an hour in the example. And this, for a hobby, is the genuinely useful figure.

Because nobody builds furniture to save money. If saving money were the goal, the answer would be to buy the table. What you’re actually buying with $519 is a large number of contented hours in a workshop — and at fifteen dollars an hour of materials, with a dining table at the end of it, that compares very favourably to most other ways of spending a Saturday.

That reframe is worth having, because it stops the costing exercise from being discouraging and turns it into something closer to the truth.

One more thing worth tracking

A small, unglamorous habit that pays for itself: log when blades and bits were last sharpened.

Burning, tearout and a cut that suddenly needs pushing aren’t usually technique problems — they’re a blade that’s been quietly getting duller for four months. Sharp tools are also safer tools, because a dull blade needs force, and force is how hands end up where they shouldn’t be.

A date and an interval is all it takes, and it turns “something’s wrong with this saw” into “the blade’s four months old.”

An important note

To be clear: this is a general explanation and a way of organizing your own figures. It is not training, safety, engineering, structural, health, or professional advice, and it guarantees no outcome. All species, dimensions, prices and figures mentioned are illustrative examples, and lumber prices vary enormously by country, species and supplier. Board-foot figures are estimates that don’t account for grain direction, defects, figure, pattern matching or your own cutting. Woodworking machinery causes serious and permanent injuries: obtain proper instruction, read and follow the manual for every tool, use the guards and safety devices supplied, and comply with the workshop, electrical and health-and-safety rules that apply where you are. Any safety checklist is a memory aid for someone already trained on their machines — it is not a substitute for training.

If you want the order calculated for you

I built a cut list into my woodworking planner in Google Sheets that handles both adjustments — enter parts in finished sizes and it works out the rough stock (4/4, 8/4, 12/4), applies a waste allowance you set once, and gives you board feet to buy totalled by species at your own prices, alongside a project cost sheet with all three of those honest numbers:

👉 Woodworking Planner, Cut List & Board Feet Calculator for Google Sheets & Excel

Whether you use mine or a notepad, do the rough-stock and waste adjustments before you go to the yard rather than in the aisle. Board feet was never the hard part — it’s the two corrections either side of it that decide whether you come home with enough wood. Measure once. Order once. 🪵

This reflects my own perspective and describes a calculation tool — NOT training, safety or engineering advice, and it guarantees no outcome; figures are illustrative and lumber prices vary enormously by country and supplier. Machinery causes serious injuries — get proper instruction and use the guards supplied. What’s your waste percentage, and has it ever been enough? Tell me in the comments.