Skip to content
Woodworking Math

8x8 actual size

Dry (19% moisture or less)

7-1/4 × 7-1/4 in

184.2 × 184.2 mm

From the standard, NIST PS 20-25

End view to scale: dashed is the nominal 8x8, filled is the dry dressed size.

Nominal, dry and green

SizeThicknessWidth
Nominal (the name)8 in8 in
Dry, minimum7-1/4 in (184.2 mm)7-1/4 in (184.2 mm)
Green, minimum7-1/2 in (190.5 mm)7-1/2 in (190.5 mm)

A 8x8 is timbers (5 in nominal thickness and up) under the American Softwood Lumber Standard, NIST PS 20-25. The standard names lumber by its nominal size and sets the smallest it may be once it has been dressed (planed smooth). Lumber dried to 19% moisture content or less is held to the dry size; lumber surfaced green, above 19%, is left a little bigger because it shrinks as it dries. The standard notes that timbers are often made and sold without drying, so expect the green size.

Board feet in a 8x8

Thickness × width ÷ 12 gives the board feet in each foot of length. By the nominal size that is 5.333 bd ft per foot; by the dry dressed size it is 4.38. Ask your yard which one it prices on.

LengthNominal bd ftActual (dry) bd ft
8 ft42.6735.04
10 ft53.3343.8
12 ft6452.56
16 ft85.3370.08

For a whole order, use the board foot calculator. Every size side by side is on the lumber sizes chart.

Framing a deck? The deck calculator says which joist, beam and post sizes span it, from the AWC DCA 6 tables.

What a 8x8 weighs per foot

One foot of a dry 8x8, 7-1/4 × 7-1/4 in, at 12% moisture content: its volume × the Wood Handbook’s density, 62.43 lb/ft³ × the species’ specific gravity at 12% × 1.12. Multiply by the length for a whole board. Wetter wood weighs more; the wood weight calculator takes any moisture content.

SpeciesSpecific gravity (12%)Weight per foot
Douglas-fir (coast)0.4812.25 lb
Southern pine (loblolly)0.5113.02 lb
Western hemlock0.4511.49 lb
Eastern white pine0.358.93 lb
White spruce0.369.19 lb

One source: USDA Forest Products Laboratory, the authority for species properties it measured

Work it out for your project

Sources

  1. NIST (US Department of Commerce), Voluntary Product Standard PS 20-25, American Softwood Lumber Standard, Table 3 (effective January 2025), read 2026-11-07
  2. Engineering ToolBox, Softwood lumber: nominal and actual (dry) sizes, read 2026-11-07
  3. WoodBin, Standard dimensions of lumber (hardwood thickness after G. Wengert; softwood dry and green sizes), read 2026-11-07

How we source these numbers