Lumber Size Chart: Nominal vs Actual

How do I use this size chart when I'm buying?

The first thing I tell anyone new to a lumber yard is that the chart below settles arguments, not the calculator. When a builder swears his joists won't fit, nine times out of ten he measured an actual 9.25″ 2x10 and expected a clean 10 inches. So I keep this table for fit questions, and I keep board-foot math on a separate page — if you're chasing the pricing number instead, start with how to calculate board feet, because that's a different question than "how wide is this board really."

A quick story on why the gap matters. I once signed off on a deck-skirting order where the carpenter had planned his gaps around a 6-inch 1x6. He counted 40 ft × 12 ÷ 6 = 80 boards. The actual board is 5.5″, so those 80 only cover 36.7 ft — 3.3 ft of band left open, and closing it meant 8 more boards (40 × 12 ÷ 5.5 = 87.3, so 88). Half an inch per board sounds like nothing until it stacks across a whole job, and that's the exact mistake this chart exists to prevent.

So my habit at the counter is blunt: I never quote a fit dimension from the nominal name. I read the actual column out loud, write it on the cut list, and let the customer plan clearances from the real number. For thickness it's even simpler — every 2x is 1.5″ every 1x is 0.75″ no exceptions in softwood. It's the width that drifts, and the chart keeps me honest on it.

What are the nominal vs actual sizes?

What is the pattern to remember?

Thickness loses ¼″ (a 2x is 1.5″). Width loses ½″ up to 6″ nominal, then ¾″ at 8″ and wider — that's why a 2x8 is 7.25″ not 7.5″.

How many boards per linear foot does each size cover?

For anything boarded edge-to-edge — skirting, decking, fence rails, shed siding, drawer banks — the count you need is 12 ÷ actual width, not 12 ÷ the name. That single division is where a "half an inch" becomes a delivery you have to make twice.

Two things in that table surprise people. First, the penalty isn't smooth: 1x8 costs you more (10.3%) than 1x10 does (8.1%), because the wider sizes jump to a ¾″ loss but are dividing it over more inches. Second, thickness is irrelevant to coverage — a 2x4 at 3.5″ wide needs the same 3.43 boards per foot as a 1x4, even though it bills twice the board feet. Cover is a width question; billing is a volume question, and the two never meet on a cut list.

Why are nominal and actual sizes different?

The nominal size is the board's dimension when it's first rough-sawn and still wet. Two things shrink it before it reaches you: kiln drying pulls moisture out and the wood contracts, and surfacing (planing all four sides smooth, "S4S") removes more material. The net loss is about ¼″ on thin members and ½″ once you pass 2 inches nominal. The name stuck because the trade has always referred to lumber by its sawn size, and changing the labels now would confuse a century of building plans.

Which board foot dimensions go into the formula?

Use the nominal numbers in the first column of the chart, because that's how softwood construction lumber is priced. Actual size matters for fit (joist depth, drawer clearances), not for the yard ticket. Watch what happens if you mix the two up on a single 1×6×8:

• Nominal (correct for softwood): 1 × 6 × 8 ÷ 12 = 4.00 BF
• Actual (0.75 × 5.5): 0.75 × 5.5 × 8 ÷ 12 = 2.75 BF

The shortcut: cross-section area, divided by 12

The two figures in any row of the chart are a cross-section, so board-foot math is really area ÷ 12, then × length in feet. A 2×6 is 12 in² nominal, and 12 ÷ 12 = exactly 1.00 BF per foot; a 2×10 is 20 in², so 20 ÷ 12 = 1.67 BF per foot; a 4×4 and a 2×8 are both 16 in² and bill identically. Once you see the sizes as areas, the per-foot rate isn't something to memorise — it falls out of the chart. The rate for every size is listed on the BF per foot for every size sheet rather than repeated here, and why the divisor is 12 instead of 144 goes back to boards, planks, deals and scantlings being sold by the foot before the trade agreed on volume — that's worked through on what a board foot is.

How much of the billed volume is actually in the truck?

Same arithmetic, run on the actual column. A surfaced 2×4 is 5.25 in² against the 8 in² on the ticket: 65.6% of the board feet you paid for. A 6×6 keeps 84.0%, because a quarter-inch off a thick square barely moves the area. That percentage is the board feet size difference that makes a load look thin, and it's what freight, kiln drying and dumpsters actually charge against — the ratios for every size, plus the cubic feet behind them, are in the cubic-feet conversion table. I don't duplicate that table here: this page is for holding a tape against a board, that one is for arguing about a truck.

That's a 31% swing on one board — multiply it across a framing package and you can see why the "wrong" calculator looks broken. Using the wrong basis is the top reason a calculator disagrees with a quote; the rest are in why calculators give different results.

Does it flip for hardwood?

It does. Hardwood is priced by actual surface measure, with thickness called in quarters (4/4, 5/4, 6/4). So for hardwood you measure the real width and length, while for softwood you trust the nominal label. I keep two mental modes for this, and honestly that's the only "trick" — know which market you're standing in. The thickness side of hardwood is its own topic in the hardwood thickness guide. For a per-size volume shortcut rather than a fit table, grab the multipliers on the cheat sheet. The same nominal/actual gap also shows up as space: a 2×6 load is only about two-thirds of the cubic feet its board-foot tally implies, which is what freight, kilns and dumpsters actually charge against — the board feet to cubic feet table runs that per size.

Frequently asked questions