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🪵 Lumber Dimensions Reference

Nominal vs actual lumber sizes, board feet, and common lumber specs.

Nominal vs Actual Sizes​

"2x4" doesn't actually measure 2" × 4". Here are the real dimensions:

Dimensional Lumber (Softwood)​

NominalActual (Dry)Actual (Green)
1 × 23/4" × 1-1/2"25/32" × 1-9/16"
1 × 33/4" × 2-1/2"25/32" × 2-9/16"
1 × 43/4" × 3-1/2"25/32" × 3-9/16"
1 × 63/4" × 5-1/2"25/32" × 5-5/8"
1 × 83/4" × 7-1/4"25/32" × 7-1/2"
1 × 103/4" × 9-1/4"25/32" × 9-1/2"
1 × 123/4" × 11-1/4"25/32" × 11-1/2"
NominalActual (Dry)Actual (Green)
2 × 21-1/2" × 1-1/2"1-9/16" × 1-9/16"
2 × 31-1/2" × 2-1/2"1-9/16" × 2-9/16"
2 × 41-1/2" × 3-1/2"1-9/16" × 3-9/16"
2 × 61-1/2" × 5-1/2"1-9/16" × 5-5/8"
2 × 81-1/2" × 7-1/4"1-9/16" × 7-1/2"
2 × 101-1/2" × 9-1/4"1-9/16" × 9-1/2"
2 × 121-1/2" × 11-1/4"1-9/16" × 11-1/2"
NominalActual (Dry)
4 × 43-1/2" × 3-1/2"
4 × 63-1/2" × 5-1/2"
6 × 65-1/2" × 5-1/2"
8 × 87-1/4" × 7-1/4"

Why the Difference?​

Lumber is measured before drying and planing:

  1. Rough cut at nominal size (2" × 4")
  2. Dried in kiln (shrinks)
  3. Planed smooth (removes more material)
  4. Final size is smaller (1-1/2" × 3-1/2")

Board Feet Calculator​

Board feet is the standard unit for lumber volume pricing.

Formula​

Board Feet = (Thickness" × Width" × Length') ÷ 12

Or using nominal dimensions:

Board Feet = (T × W × L) ÷ 12

Quick Reference​

Size8' Length10' Length12' Length
1×42.67 BF3.33 BF4.0 BF
1×64.0 BF5.0 BF6.0 BF
1×85.33 BF6.67 BF8.0 BF
1×106.67 BF8.33 BF10.0 BF
1×128.0 BF10.0 BF12.0 BF
2×45.33 BF6.67 BF8.0 BF
2×68.0 BF10.0 BF12.0 BF
2×810.67 BF13.33 BF16.0 BF
2×1013.33 BF16.67 BF20.0 BF
2×1216.0 BF20.0 BF24.0 BF

Standard Lengths​

Dimensional Lumber​

  • 8', 10', 12', 14', 16', 18', 20'
  • Some specialty: 22', 24'

Studs (Pre-Cut)​

Ceiling HeightStud Length
8' ceiling92-5/8" (7'8-5/8")
9' ceiling104-5/8" (8'8-5/8")
10' ceiling116-5/8" (9'8-5/8")

Lumber Grades​

Dimension Lumber (2×4, 2×6, etc.)​

GradeUseNotes
Select StructuralEngineered applicationsHighest strength
No. 1General framingGood strength, few defects
No. 2General framingMost common grade
No. 3Non-structuralLower strength allowed
StudWall studsSpecifically graded for studs

Appearance Grades (Boards)​

GradeQuality
Select B & BetterFinest appearance
C SelectHigh quality, few defects
D SelectGood quality
No. 1 CommonKnotty, sound
No. 2 CommonMore knots, some defects

Common Species​

Softwoods (Framing)​

SpeciesStrengthUseNotes
Douglas Fir-LarchHighStructuralMost common framing
Southern PineHighStructural, treatedTakes treatment well
Hem-FirMediumGeneral framingLighter than Doug Fir
SPF (Spruce-Pine-Fir)MediumGeneral framingEconomy choice

Pressure Treated​

Retention LevelUse
.25Above ground
.40Ground contact
.60Ground contact, fresh water
2.50Salt water, foundation

Engineered Lumber​

LVL (Laminated Veneer Lumber)​

DepthCommon WidthsTypical Use
9-1/2"1-3/4", 3-1/2"Headers, beams
11-7/8"1-3/4", 3-1/2"Beams, girders
14"1-3/4", 3-1/2"Long spans
16"1-3/4", 3-1/2"Long spans
18"1-3/4", 3-1/2"Heavy loads

I-Joists​

DepthFlangeUse
9-1/2"1-1/2" or 2-5/16"Short spans
11-7/8"1-1/2" or 2-5/16"Common floors
14"1-1/2" or 2-5/16"Longer spans
16"1-1/2" or 2-5/16"Long spans

Glulam (Glued Laminated Timber)​

WidthDepths Available
3-1/8"6" to 24"+
5-1/8"6" to 30"+
6-3/4"9" to 36"+

Quick Conversions​

Linear Feet to Board Feet​

SizeMultiply LF by
1×40.333
1×60.5
1×80.667
1×121.0
2×40.667
2×61.0
2×81.333
2×101.667
2×122.0

Pieces per MBF (1,000 Board Feet)​

Size × 8'Pieces
2×4×8187
2×6×8125
2×8×893
2×10×875
2×12×862