Building supply stores commonly sell lumber by the piece, but lumber mills and some hardwood dealers price according to the board foot.

Ask for a dozen 2x4s eight feet long at your local sawmill, and they’ll say you want 64 board feet of lumber. 

If you want to read up on lumber mills, then bookmark our article on lumber mills and their unique process before you continue below to learn about calculating board feet.


How to Calculate Board Feet

It’s not as confusing as it sounds, as long as you remember that a board foot is a measure of volume equal to a square foot one inch thick. So a 1″ x 12″ board that is 1′ long and a 2″ x 6″ board of the same length both equal one board foot.

Use the lumber’s nominal dimensions, as opposed to its actual dimensions, when calculating board feet. Nominal measurements refer to the size before it’s planed and dried, whereas actual measurements represent the size after that process. For example, the actual dimensions of a 2×4 may be 1.5″ by 3.5″, while it’s the nominal dimensions that are 2″ by 4″.

To calculate board feet, use this formula:‌

Thickness (inches) x width (inches) x length (feet) ÷ 12 = board feet

For example, to determine how many board feet are in a 2x4x10, apply the formula:

(1.5” x 3.5” x 10’) / 12 = 4.375 board feet.

You can indicate your result using any of the following abbreviations for board feet:

  • FBM
  • BDFT
  • BF
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Alternatively, you can use this formula: Thickness (inches) x width (inches) x length (inches) ÷ 144 = board feet

This simple equation provides clarity on how many board feet are in various lumber sizes, ensuring you can confidently plan your woodworking or construction projects with precision. 


Calculating Board Feet for a Project

When estimating the cost of a woodworking or construction project, it’s vital to accurately calculate the lumber you’ll need. 

Here are tips for calculating your project’s board feet:

  • Take detailed measurements of all wooden components needed, including length, width, and thickness of boards, beams, trim, etc. Measure precisely — even small errors can affect your totals.
  • If using plans, verify they match your actual dimensions. Adjust if necessary.
  • For dimensional lumber (2x4s, 2x6s), round up to the next whole foot. For example, an 8’4″ board would count as 9′.
  • For hardwood boards, use the exact inches needed — don’t round.
  • Use the formula above to calculate board feet for each piece.
  • Add up all components’ totals to get the total board feet required.
  • Add 10–15% for waste, mistakes, and off-cuts. It’s better to have a surplus of lumber rather than not enough.

Precisely calculating board feet helps avoid headaches and unplanned costs during your build.


lumber project
Image Credit: Canva

Board Foot Pricing

Since lumber is priced and sold by the board foot, accurate calculations are vital for budgeting costs.

Pricing varies widely depending on:

Construction lumber is inexpensive, while domestic and exotic hardwoods range from moderate to very expensive per board-foot.

Higher appearance grade prices reflect flawless looks. Lower grades with more knots and markings are affordable.

Rough-sawn lumber is cheaper than surfaced lumber that’s planed smooth. Kiln drying adds cost over air drying.

Buying in bulk means a lower cost per board foot. Small purchases often pay more per board foot.

Lumberyards or sawmills selling wholesale charge less per board foot than big box stores.

Research current prices for your specific lumber to accurately budget. Prices fluctuate regularly based on supply and demand.


Board Foot Calculators

These calculators can help with the math:

Today’s Homeowner Calculators

Additional Online Calculators

These tools can help double-check calculations for accuracy.


So, Is Understanding Lumber Measurements Helpful?

Yes, a solid grasp of board feet, pricing, and estimating is very helpful for any woodworking or construction project. Doing the math ahead of time and understanding your exact material requirements saves money, prevents shortages/overages, and gives confidence at the project’s start. While the board foot system seems confusing initially, these formulas are simple once learned. Taking the time to accurately calculate your needs is a key first step to an efficient, cost-effective build.


FAQs About Lumber Measurements

What size is a board foot?

A board foot equals 1 inch thick, 12 inches wide, and 12 inches long – 144 cubic inches of wood.


How do I calculate board feet?

Use the formula:

Board feet = (Thickness” x Width” x Length’) / 12


Is a 2x4 really 2 by 4 inches?

No, milled lumber is slightly undersized. The actual dimensions of a 2×4 are more like 1.5” x 3.5” inches. 2×4 refers to the nominal dimensions of the wood prior to drying and smoothing.


How much does a board foot of lumber cost?

It varies widely, from under $1 for basic construction lumber to over $10 for premium exotic hardwoods. Check current prices when budgeting.


Should I round lumber measurements?

For dimensional lumber, round up to the next whole foot. For specialty exotic wood and hardwoods, use exact measurements.


Editorial Contributors
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Doug Sluga

Doug Sluga is a professional roofer and carpenter with ten years of experience in residential and commercial construction. His expertise spans the breadth of the roofing trade from minor repairs to laying shingles to framing trusses. These days he spends most of his time writing about roofing and the roofing industry.

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Andrew Foligno

Andrew Foligno is an editor for Today’s Homeowner, with over 6 years of experience working in digital marketing. He started his career as a content writer at an agency, covering industries such as HVAC, plumbing, painting, lawn care, and more. Soon, he was promoted to an editor position where he oversaw a team of writers before moving on to other facets of digital marketing. When he isn’t working, Andrew enjoys going to the gym to be active, as well as going to the movies to unwind.

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