Quick Answer: A 1x6 board measures exactly 3/4 inch thick by 5-1/2 inches wide — not 1 inch by 6 inches. The reduction comes from milling: rough lumber dries and shrinks, then a planer surfaces all four sides to a uniform finished size.
1x6 Dimension Table — Nominal vs. Actual
The "1x6" you ask for at the counter is a label, not a measurement. What lands on your truck is the surfaced size below.
| Designation | Actual thickness | Actual width | Notes |
|---|---|---|---|
| 1x6 nominal (S4S) | 3/4" | 5-1/2" | What every big-box and lumber yard sells as a "1x6" |
| 5/4x6 (five-quarter) | 1" | 5-1/2" | A full inch thick — common for stair treads and outdoor decking |
| 1x6 rough-sawn | ~1" | ~6" | Pre-surfacing dimensions; you mill these yourself |
| 1x6 hardwood (S2S, random width) | 13/16" | varies | Hardwood mills surface 4/4 stock to 13/16", widths random |
Length is sold in 2-foot increments — typically 6, 8, 10, 12, and 16 feet — and the length stamp is honest. Only thickness and width shrink.
Frequently Asked Questions
What is the actual size of 1x6 lumber?
A surfaced ("S4S") 1x6 measures 3/4 inch thick by 5-1/2 inches wide. Length is whatever the tag says — a 1x6x8 is a true 8 feet long. The 3/4 × 5-1/2 figure is consistent across pine, fir, cedar, poplar, and oak when sold as a softwood-spec dimensional 1x6. Hardwoods sold as 4/4 stock are slightly thicker (13/16") because hardwood mills surface less material off.
Why is 1x6 lumber not actually 1×6?
Rough lumber comes off the saw at a full inch by a full six inches. Then it dries — losing 5–10% in width as moisture leaves — and a planer shaves all four sides to remove cup, twist, and saw marks. What's left is the smooth, uniform 3/4" × 5-1/2" board you buy. The "1x6" name stuck from the rough size before drying and planing because it's how mills priced and tallied the cut. The American Softwood Lumber Standard PS 20 codifies the finished sizes today, and Lowe's nominal vs. actual reference confirms big-box stores follow the same spec.
When should I use 5/4x6 instead of 1x6?
Reach for 5/4x6 ("five-quarter") when 3/4 inch isn't strong enough. Most decking is 5/4x6 because the extra 1/4 inch of thickness means less deflection between joists. Stair treads, outdoor benches, and any horizontal surface that supports weight or spans more than ~16 inches benefits from the upgrade. Indoor shelving, trim, painted furniture, and small projects are fine on 1x6. If your span is over 24 inches, consider 5/4x6 or add a support — see the 1x6 buying guide for species and spans.
What does S4S mean on lumber tags?
S4S means "surfaced four sides" — the board has been planed smooth on both faces and both edges. That's the standard finish for big-box dimensional lumber. S2S means surfaced on the two faces only, with rough or saw-cut edges (common for hardwoods sold by random width). Rough-sawn means none of the surfaces have been planed; the board still shows saw marks and is sold at the larger pre-milling dimensions. S4S boards are ready to use; S2S and rough-sawn need jointing or planing first.
For species, grade selection, and project-specific picks, see the 1x6 lumber buying guide.
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