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Lumber Sizing Guide

Dimensions, board foot calculations, grading standards, species properties, and the critical differences between reclaimed and modern lumber sizing. Everything you need in one place.

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Nominal vs Actual Dimensions Board Foot Calculator Lumber Grading Standards Reclaimed Wood Grading Wood Species Properties Reclaimed Lumber Dimensions

Nominal vs Actual Dimensions

When you buy a “2x4” from any modern lumber yard, you are not getting a board that measures 2 inches by 4 inches. After kiln drying and surfacing (planing smooth), the actual dimensions shrink significantly. This discrepancy between the named size (nominal) and the real measurement (actual) is one of the most common sources of confusion in the lumber industry.

The nominal size refers to the rough-sawn dimension of the board before drying and planing. The actual size is what you receive. Modern dimensional lumber standards were formalized by the American Lumber Standard Committee (ALSC) and are codified in the PS 20 voluntary product standard. The table below shows standard nominal-to-actual conversions for softwood dimensional lumber.

Nominal Size	Actual Size (inches)	Actual Size (mm)	Common Uses
1 x 2	3/4" x 1-1/2"	19 x 38	Furring strips, lattice
1 x 3	3/4" x 2-1/2"	19 x 64	Trim, battens
1 x 4	3/4" x 3-1/2"	19 x 89	Trim, shelving, craft
1 x 6	3/4" x 5-1/2"	19 x 140	Fencing, shelving, paneling
1 x 8	3/4" x 7-1/4"	19 x 184	Shelving, sheathing
1 x 10	3/4" x 9-1/4"	19 x 235	Wide shelving, paneling
1 x 12	3/4" x 11-1/4"	19 x 286	Shelving, cabinet sides
2 x 2	1-1/2" x 1-1/2"	38 x 38	Balusters, stakes, furring
2 x 4	1-1/2" x 3-1/2"	38 x 89	Wall framing, general construction
2 x 6	1-1/2" x 5-1/2"	38 x 140	Floor/wall framing, decking
2 x 8	1-1/2" x 7-1/4"	38 x 184	Floor joists, rafters, headers
2 x 10	1-1/2" x 9-1/4"	38 x 235	Floor joists, rafters, beams
2 x 12	1-1/2" x 11-1/4"	38 x 286	Floor joists, stair stringers
4 x 4	3-1/2" x 3-1/2"	89 x 89	Posts, columns, railings
4 x 6	3-1/2" x 5-1/2"	89 x 140	Beams, posts, headers
6 x 6	5-1/2" x 5-1/2"	140 x 140	Heavy posts, columns, timbers
6 x 8	5-1/2" x 7-1/2"	140 x 190	Beams, timber framing
8 x 8	7-1/2" x 7-1/2"	190 x 190	Heavy beams, timber framing

Important Note for Hardwood Lumber

Hardwood lumber is sold differently than softwood dimensional lumber. Hardwood is typically sold by thickness in quarter-inch increments: 4/4 (four-quarter) = 1 inch rough, 5/4 = 1.25 inches rough, 6/4 = 1.5 inches rough, 8/4 = 2 inches rough, and so on. After surfacing (S2S), expect to lose approximately 3/16 inch from each face. So a 4/4 board surfaced two sides yields approximately 13/16 inch. Widths and lengths are random and sold by the board foot.

Board Foot Calculation Guide

A board foot is the standard unit of volume measurement for lumber in North America. One board foot equals a piece of wood that is 1 inch thick, 12 inches wide, and 12 inches long (144 cubic inches). Understanding board feet is essential for pricing, estimating, and ordering lumber.

The Formula

Board Feet = (Thickness" x Width" x Length') / 12

Thickness and width in inches, length in feet

Alternatively, if all measurements are in inches:

Board Feet = (Thickness" x Width" x Length") / 144

All dimensions in inches

Worked Examples

Example 1: Standard Board

A board that is 1 inch thick, 6 inches wide, and 8 feet long:

BF = (1 x 6 x 8) / 12 = 48 / 12 = 4 board feet

Example 2: Thick Plank

A plank that is 2 inches thick, 10 inches wide, and 12 feet long:

BF = (2 x 10 x 12) / 12 = 240 / 12 = 20 board feet

Example 3: Timber Beam

A reclaimed beam that is 8 inches x 8 inches and 16 feet long:

BF = (8 x 8 x 16) / 12 = 1024 / 12 = 85.33 board feet

Example 4: Multiple Boards

You need 25 boards, each 1 inch thick, 8 inches wide, and 10 feet long. How many total board feet?

Per board: (1 x 8 x 10) / 12 = 6.67 BF
Total: 6.67 x 25 = 166.67 board feet

Quick Reference: Board Feet per Lineal Foot

For fast estimating, use this table showing how many board feet are in one lineal (running) foot of common lumber sizes.

Size	BF per Lineal Foot	BF in 8' board	BF in 12' board	BF in 16' board
1 x 4	0.33	2.67	4.00	5.33
1 x 6	0.50	4.00	6.00	8.00
1 x 8	0.67	5.33	8.00	10.67
1 x 12	1.00	8.00	12.00	16.00
2 x 4	0.67	5.33	8.00	10.67
2 x 6	1.00	8.00	12.00	16.00
2 x 8	1.33	10.67	16.00	21.33
2 x 10	1.67	13.33	20.00	26.67
2 x 12	2.00	16.00	24.00	32.00
4 x 4	1.33	10.67	16.00	21.33
6 x 6	3.00	24.00	36.00	48.00
8 x 8	5.33	42.67	64.00	85.33

Lumber Grading Standards

Lumber grading is a standardized system for classifying wood based on its structural integrity, appearance, and number of defects. Grades are established by grading agencies certified under the American Lumber Standard Committee. Understanding grades helps you specify the right material for your project without overpaying for quality you do not need or underspecifying for a structural application.

Select Structural

The highest structural grade. Tight knots only (if any), straight grain, no wane, no splits. Excellent strength properties. Used for exposed structural applications where appearance and strength both matter: ridge beams, exposed rafters, timber-frame joinery.

Allowable Defects:

Knots limited to 1/4 of face width. No wane. No shake. Slope of grain no steeper than 1:12.

#1 Grade

High quality with minor defects. Sound, tight knots are permitted. Good structural capacity. The go-to grade for most framing and structural applications where the lumber will be concealed (inside walls, under floors). Also suitable for visible applications where small knots add character.

Allowable Defects:

Knots up to 1/3 of face width. Slight wane permitted on edges. Minor checking allowed. Slope of grain no steeper than 1:10.

#2 Grade

The most commonly sold structural grade. Permits larger knots and more character than #1 but still carries good structural ratings. Widely used for general framing (studs, joists, rafters) and non-appearance applications. Most standard framing lumber at retail yards is #2 or better.

Allowable Defects:

Knots up to 1/2 of face width. Wane up to 1/3 of edge. Moderate checking. Occasional skip in surfacing.

#3 Grade

Economy structural grade. Larger defects permitted. Reduced structural values compared to #1 and #2. Suitable for non-critical framing, blocking, bracing, temporary construction, and applications where appearance is not a concern.

Allowable Defects:

Knots up to 2/3 of face width. Significant wane permitted. Splits up to board width. Loose knots allowed.

Economy / Utility

Below structural grade. Not recommended for load-bearing applications without engineering review. Suitable for temporary bracing, crating, packaging, and non-structural projects like garden beds, compost bins, and shop jigs.

Allowable Defects:

Unlimited knot size. Heavy wane. Splits. Decay permitted if not structurally compromising. Significant bow, twist, or crook.

Appearance Grades (Non-Structural)

For hardwood and finish-grade softwood, appearance grades replace structural grades. The National Hardwood Lumber Association (NHLA) defines these grades based on the percentage of clear, defect-free cuttings that can be obtained from each board.

NHLA Grade	Min. Clear Cuttings	Min. Board Size	Typical Use
FAS (First & Seconds)	83-1/3%	6" x 8'	Fine furniture, cabinetry, high-end millwork
FAS One Face (F1F)	83-1/3% (one face)	6" x 8'	Furniture where one face is hidden
#1 Common	66-2/3%	3" x 4'	General furniture, cabinets, mouldings
#2A Common	50%	3" x 4'	Paneling, craft, character furniture
#2B Common	50%	3" x 4'	Similar to 2A with slightly smaller min. cuttings
#3A Common	33-1/3%	3" x 4'	Flooring, crating, pallets, small projects

Reclaimed Wood Grading

Standard ALSC and NHLA grading systems were designed for freshly milled lumber. Reclaimed wood does not fit neatly into these categories because the types of defects are different. A reclaimed board might have perfectly straight, tight grain with zero knots but carry nail holes, bolt slots, and surface checking from age. At Philadelphia Lumber Co., we use an adapted grading system that accounts for the unique character of salvaged material.

Premium / A Grade

The cleanest reclaimed material available. Minimal nail holes (fewer than 2 per lineal foot), no rot, no structural damage. Surface may show age patina and minor weathering but is free of deep checks and cracks. Suitable for fine furniture, high-end residential flooring, and visible architectural features. This grade represents roughly 10-15% of a typical reclaimed lumber batch.

Character / B Grade

Sound, structurally solid boards with moderate character marks: nail holes, bolt holes, minor checking, surface oxidation, and occasional worm tracks. This is the sweet spot for most residential and commercial projects where you want the reclaimed aesthetic without compromising structural integrity. Makes excellent flooring, accent walls, shelving, and tabletops. Represents 40-50% of typical batches.

Rustic / C Grade

Heavy character: large nail holes, significant checking, surface roughness, knot holes, and staining. Structurally sound for non-load-bearing applications but not recommended for structural use without engineering review. Ideal for barn-style accent walls, rustic furniture, garden structures, and artistic installations where the weathered look is the entire point.

Structural Reclaimed

Graded independently for structural capacity rather than appearance. These beams and timbers have been inspected for rot, insect damage, cross-grain cracking, and load-bearing section loss. Suitable for post-and-beam construction, floor joists, and headers when used within the assigned span tables. May carry any appearance grade. Always supplied with a grading certificate when used in permitted construction.

Key Difference from New Lumber Grading

New lumber grading focuses primarily on natural defects: knots, slope of grain, wane, and splits. Reclaimed grading adds a second dimension: human-made defects from previous use (nail holes, notches, hardware marks) plus age-related changes (checking, patina, mineral staining). A reclaimed board with zero knots and perfectly straight grain might still grade B or C due to bolt holes from its original installation. This is why reclaimed grading cannot simply borrow the NHLA or ALSC systems unchanged.

Common Wood Species & Properties

Different wood species vary dramatically in hardness, weight, durability, and workability. The table below covers the most common species we encounter in both new and reclaimed lumber. The Janka hardness rating measures resistance to denting and wear. Higher numbers indicate harder wood. Weight is given as air-dried density at approximately 12% moisture content.

Species	Type	Janka Hardness (lbf)	Weight (lbs/ft3)	Decay Resistance	Common Reclaimed Sources
White Oak	Hardwood	1,360	47	Excellent	Barn frames, whiskey barrels, ship planking
Red Oak	Hardwood	1,290	44	Poor	Flooring, factory beams, rail ties
American Chestnut	Hardwood	1,010	30	Excellent	Barn siding, fencing, timber frames (rare)
Heart Pine (Longleaf)	Softwood	1,225	36	Good	Factory floors, joists, beams, warehouse decking
Douglas Fir	Softwood	660	34	Moderate	Warehouse beams, bridge timbers, rail trestles
Eastern White Pine	Softwood	380	25	Poor	Barn siding, wide-plank flooring, trim
Poplar (Tuliptree)	Hardwood	540	29	Poor	Siding, trim, interior framing
Hard Maple	Hardwood	1,450	44	Poor	Bowling alleys, factory floors, gym floors
Black Walnut	Hardwood	1,010	38	Good	Furniture, gunstocks, trim (less common reclaimed)
Cherry	Hardwood	950	35	Poor	Furniture, cabinetry (rare in reclaimed)
Cypress (Bald)	Softwood	510	32	Excellent	Water tanks, siding, outdoor structures, boat planking
Western Red Cedar	Softwood	350	23	Excellent	Siding, shingles, fence posts, decking
Hemlock	Softwood	500	28	Poor	Barn frames, general construction, crating
Elm (American)	Hardwood	830	35	Poor	Wagon wheels, bent parts, barn structure
Ash (White)	Hardwood	1,320	42	Poor	Tool handles, sports equipment, flooring

Why Janka Hardness Matters

The Janka test measures the force required to embed a 0.444-inch steel ball to half its diameter into the wood surface. For flooring, a Janka rating above 1,000 is recommended for residential use and above 1,200 for commercial. Reclaimed heart pine, with a Janka of 1,225, is one of the few softwoods hard enough for commercial flooring. By contrast, modern plantation-grown southern yellow pine rates only 690, illustrating how old-growth wood differs from modern timber.

Decay Resistance Ratings Explained

Decay resistance indicates how well the heartwood resists fungal rot when exposed to moisture and ground contact. Species rated “Excellent” (white oak, chestnut, cypress, cedar) can be used in outdoor and ground-contact applications without chemical treatment. Species rated “Poor” require preservative treatment or protective finishes for any outdoor use. Note that sapwood of all species is non-durable regardless of the heartwood rating.

Special Considerations for Reclaimed Lumber Dimensions

One of the most important things to understand about reclaimed lumber is that it often does not follow modern dimensional standards. This is actually a significant advantage once you understand it.

True to Nominal Size

Before the 1960s, lumber standards allowed much less reduction from nominal size during drying and surfacing. Many older mills sold lumber rough-sawn with no planing at all. As a result, a reclaimed 2x4 from a pre-1960 barn often measures a full 2 inches by 4 inches, or very close to it. A reclaimed 2x12 frequently measures 1-7/8 inches to 2 inches thick and 11-1/2 to 12 inches wide.

This means reclaimed lumber gives you more material per piece than modern lumber. A reclaimed 2x10 has roughly 18% more cross-sectional area than a modern 2x10. For structural applications, this translates directly into greater load capacity. For flooring and paneling, it means wider, thicker boards that feel more substantial underfoot.

Dimensional Variability

The flip side of true nominal sizing is inconsistency. A stack of reclaimed 2x6 boards from the same barn might vary in thickness from 1-3/4 inches to 2-1/8 inches and in width from 5-1/2 inches to 6-1/4 inches. This variability is a natural consequence of the era in which the wood was originally milled, differences in sawing technique, and decades of differential shrinkage and wear.

For projects requiring uniform dimensions, plan on having your reclaimed lumber milled to a consistent target size. We recommend specifying a target dimension that accommodates the smallest board in the batch. For example, if your 2x6 batch ranges from 1-3/4 to 2-1/8 inches thick, mill everything to 1-5/8 inches for a clean, uniform result with minimal waste.

Mixing Reclaimed and Modern Lumber

When a project combines reclaimed and modern lumber, the dimensional mismatch requires careful planning. A reclaimed 2x4 at true 2x4 will not sit flush with a modern 2x4 at 1-1/2 x 3-1/2. For framing, this means shimming, furring, or milling the reclaimed stock down to match modern dimensions.

Our custom milling service can dimension reclaimed lumber to exactly match modern sizes if needed. Alternatively, we can surface all faces while preserving the larger dimensions, and your framer can accommodate the difference with standard construction techniques. Discuss your approach with your builder before ordering to avoid surprises on the job site.

Ordering and Estimating Tips

Order 15-20% extra. Reclaimed lumber has a higher cull rate than new lumber due to hidden defects that only become apparent during milling. Budget for waste and you will not be caught short.
Specify finished dimensions, not nominal. Tell us the final thickness, width, and length you need. We will calculate the rough stock required to achieve that finished size after milling.
Ask about available lengths. Reclaimed lumber comes in whatever length it was originally installed. We may have 18-foot warehouse joists or 6-foot barn siding. Available lengths depend on current inventory.
Consider board foot pricing. Reclaimed lumber is typically priced per board foot based on nominal (rough) dimensions, not finished dimensions. Milling services are priced separately per board foot or per lineal foot depending on the operation.
Visit our yard. Reclaimed lumber is best selected in person. Photos cannot fully convey grain character, color variation, and defect patterns. We welcome walk-in visits Monday through Saturday.

Need Help Sizing Your Order?

Our team has decades of experience estimating lumber quantities for projects of every scale. Send us your plans, cut list, or project description and we will calculate exactly what you need, including the waste factor for reclaimed material.

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