How to Calculate Wood CFT: Correct Formula & Worked Example

The correct CFT (cubic feet) formula for wood depends on what units you measured in. If length, width, and thickness are all in feet, CFT = Length × Width × Thickness — no division needed. If you measured width and thickness in inches (the far more common real-world case, since a tape measure reads inches for board dimensions), the formula is CFT = Length (ft) × Width (in) × Thickness (in) ÷ 144.

That distinction matters more than it sounds. Most wood CFT guides online show only one version of the formula and apply it to every measurement blindly — which is exactly how a correct set of measurements turns into a wrong CFT number. Below is the real formula for both cases, a worked example for each, and the specific mistake that causes most CFT calculation errors.

The Correct CFT Formula for Wood (Step-by-Step)

Case 1 — all three measurements in feet. This is the simplest case: multiply the three dimensions directly, no conversion step at all.

CFT = Length (ft) × Width (ft) × Thickness (ft)

Worked example: a rough log section measuring 12 ft long, 1.5 ft wide, and 1 ft thick.
CFT = 12 × 1.5 × 1 = 18 CFT.

Case 2 — length in feet, width and thickness in inches. This is the practical, everyday case for sawn lumber, because a tape measure naturally gives you width and thickness in inches on a standard board. The formula becomes:

CFT = [Length (ft) × Width (in) × Thickness (in)] ÷ 144

The 144 isn’t an arbitrary constant — it’s there because 144 square inches equal 1 square foot. Multiplying width by thickness (both in inches) gives you the board’s cross-sectional area in square inches; dividing by 144 converts that area to square feet; multiplying by the length in feet then gives you cubic feet. Skip that logic and it’s easy to see why the formula only works when the 144 matches the units you actually measured in.

Worked example: a sawn plank 10 ft long, 8 in wide, and 2 in thick.
CFT = (10 × 8 × 2) ÷ 144 = 160 ÷ 144 = 1.11 CFT.

Why Many Online CFT Calculators Give the Wrong Answer

Here’s the mistake that’s easy to make and hard to catch, because the calculator still spits out a number that looks plausible: dividing by 144 when your measurements are already in feet. If you take that first worked example above — a 12 ft × 1.5 ft × 1 ft log — and run it through a calculator that always divides by 144, you get 12 × 1.5 × 1 ÷ 144 = 0.125 CFT. That’s off by a factor of 144. A real 18-cubic-foot log doesn’t shrink to an eighth of a cubic foot because you plugged it into the wrong formula.

The reverse mistake happens too: treating inch measurements as if they were feet and skipping the division entirely, which inflates the result by the same factor of 144. Either error is silent — the calculator doesn’t warn you, and the number still looks like a real dimension. The only fix is knowing which formula applies to the units you actually measured, which is the whole reason this page leads with both versions instead of one generic formula.

CFT vs. Board Foot: How They’re Related

Board feet and cubic feet measure the same thing — wood volume — at two different scales, and they’re often confused because both show up on the same lumber invoice. A board foot is a fixed unit: a piece of wood 1 inch thick, 12 inches wide, and 12 inches (1 foot) long. A cubic foot (CFT) is a full 12 × 12 × 12-inch cube. Because a cubic foot is exactly 12 times the volume of a board foot, the conversion is simple:

Measurement	Equivalent
1 CFT	12 board feet
1 board foot	1/12 CFT (0.0833 CFT)

Worked example: the sawn plank from earlier came out to 1.11 CFT. In board feet, that’s 1.11 × 12 = 13.3 board feet. If a supplier quotes you a price per board foot and you only have a CFT figure (common when buying from a mill that prices timber by CFT, which is standard practice in the South Asian and Southeast Asian timber trade), multiplying by 12 converts it instantly.

Measuring Wood Accurately Before You Calculate

The formula is only as accurate as the measurements you feed into it. A few habits make a real difference:

• Measure at the narrowest point on a tapered log. Logs and rough timber rarely have a perfectly uniform cross-section. Measuring at the widest point overstates the usable volume; measuring at the narrowest point (or averaging several points along the length) gives a more realistic figure.
• Keep units consistent within a single calculation. Decide up front whether you’re working in all-feet or feet-plus-inches, and don’t mix a foot measurement for length with an inch measurement for width without applying the ÷144 conversion.
• Round after you calculate, not before. Rounding a 7.6-inch width down to 7.5 inches before multiplying compounds the error across the whole calculation. Do the full-precision math first, then round the final CFT figure.
• Round up, not down, when ordering material. If your calculation comes out to 13.3 board feet, order 14. Rounding down to save a few dollars is how projects come up short mid-build.

Other Factors That Affect Accuracy

Moisture content changes a board’s actual dimensions. Green (freshly cut, unseasoned) wood is larger than the same board once it’s dried, because wood shrinks across its width and thickness as moisture leaves it — length barely changes. If you measure green lumber and calculate CFT, expect the dried figure to come in a bit lower; this is a separate effect from a math error, and it’s why mills sometimes quote both a green and a dried volume for the same order.

Species and grain don’t change the CFT formula itself, but they do affect how much usable material you actually get out of that volume. Heavy knotting, wane (bark edge), and irregular grain can mean a board with a calculated CFT of 1.11 yields noticeably less clear, usable lumber than a straight-grained board of the identical dimensions.

Where CFT Is Actually Used

In the United States, most retail lumber is priced and sold in board feet, so CFT shows up less often at the local lumberyard. It’s still the standard commercial unit for pricing sawn timber and logs in much of the South Asian timber trade (India, Pakistan, Bangladesh in particular), where “CFT rate” is how mills quote a price per cubic foot of wood. If you’re importing timber, buying from a mill that prices by CFT, or working from specs written in CFT, converting to board feet with the table above lets you compare it directly to a U.S. lumberyard quote.

Closer to home, CFT (or its cubic-foot equivalent) is also how you’d estimate the volume of wood needed for a deck or framing project, size a load for transport, or figure out how much material a stack of rough-sawn lumber actually represents before it’s milled down to finished dimensions.

Frequently Asked Questions

How do you calculate wood CFT?

If all three measurements are in feet, multiply them directly: CFT = Length × Width × Thickness. If width and thickness are in inches (the common case for sawn lumber), use CFT = [Length (ft) × Width (in) × Thickness (in)] ÷ 144.

What is the formula for wood CFT when measurements are in inches?

CFT = [Length (ft) × Width (in) × Thickness (in)] ÷ 144. The 144 converts the width-times-thickness cross-sectional area from square inches to square feet before multiplying by the length.

How many board feet are in one CFT?

One CFT equals 12 board feet, since a board foot is defined as 1 inch thick by 12 inches wide by 12 inches long, and a cubic foot is 12 times that volume.

What’s the most common mistake when calculating wood CFT?

Applying the ÷144 step to measurements that are already in feet (or skipping it when they’re in inches). Both mistakes are silent — the calculator still returns a number, just one that’s off by a factor of 144.

Conclusion

Calculating wood CFT correctly comes down to matching the formula to your units: multiply straight across if everything’s in feet, or divide by 144 if width and thickness are in inches. Measure carefully, keep your units consistent, and round up when you’re ordering material rather than calculating it. Get those three things right and the CFT figure you land on will hold up whether you’re pricing a mill order or planning a build.