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Lumber Size Converter
Find the real size of nominal lumber. Pick a size like 2×4, 4×4 or 1×6 to get its actual dressed dimensions in inches and millimetres, its length in metric, the board feet and a full nominal-to-actual chart.
Last updated:
Nominal size
ft
Enter your values to see the result.
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How to use the Lumber Size Converter
- Pick the nominal thickness and width, for example 2 and 4 for a 2×4.
- Enter the length in feet and how many boards you have.
- Choose the lumber type: dry dressed is standard store lumber.
- Press Convert to get the actual size in inches and mm.
- Use the chart to compare other common sizes.
Nominal vs actual lumber size chart
| Nominal | Actual (dry, inches) | Actual (mm) | Common uses |
|---|---|---|---|
| 1×2 | 3/4 × 1-1/2 | 19 × 38 | Furring strips, trim |
| 1×4 | 3/4 × 3-1/2 | 19 × 89 | Trim, shelving, crafts |
| 1×6 | 3/4 × 5-1/2 | 19 × 140 | Fence pickets, siding, shelves |
| 1×8 | 3/4 × 7-1/4 | 19 × 184 | Shelving, fascia |
| 1×12 | 3/4 × 11-1/4 | 19 × 286 | Wide shelves, stair skirts |
| 5/4×6 | 1 × 5-1/2 | 25 × 140 | Deck boards, stair treads |
| 2×4 | 1-1/2 × 3-1/2 | 38 × 89 | Wall studs, framing |
| 2×6 | 1-1/2 × 5-1/2 | 38 × 140 | Exterior walls, decking, rafters |
| 2×8 | 1-1/2 × 7-1/4 | 38 × 184 | Floor joists, rafters |
| 2×10 | 1-1/2 × 9-1/4 | 38 × 235 | Joists, headers, stair stringers |
| 2×12 | 1-1/2 × 11-1/4 | 38 × 286 | Joists, stringers, beams |
| 4×4 | 3-1/2 × 3-1/2 | 89 × 89 | Deck and fence posts |
| 4×6 | 3-1/2 × 5-1/2 | 89 × 140 | Beams, posts, landscaping |
| 6×6 | 5-1/2 × 5-1/2 | 140 × 140 | Heavy posts, pergolas |
Sizes follow the American Softwood Lumber Standard (NIST PS 20) for dry lumber (19% moisture content or less). Canadian lumber uses the same sizes, which is why metric catalogues list a 2×4 as 38 × 89 mm.
Tips when planning with real sizes
- Plan with actual dimensions. Two 2×4s nailed together are 3″ thick, not 4″; four 1×6 boards side by side cover 22″, not 24″.
- Pressure-treated lumber is often sold wet and can be slightly larger at first, then shrink as it dries.
- Hardwoods are sold differently. They use quarter-inch thickness (4/4, 5/4, 8/4) in random widths; 4/4 surfaced two sides is usually about 13/16″.
- Measure before cutting joinery. Mills vary by up to 1/16″, especially in width.
Frequently asked questions
What is the actual size of a 2×4?
A dry dressed 2×4 is 1-1/2" × 3-1/2" (38 × 89 mm). It started as a rough 2" × 4" board, and drying and planing (surfacing four sides) remove about 1/2".
Why is lumber smaller than its name?
The nominal size is the rough-sawn size before the wood is dried and planed smooth. The American Softwood Lumber Standard (PS 20) sets the finished sizes, so a 2×6 is always 1-1/2" × 5-1/2" and a 1×8 is 3/4" × 7-1/4".
What is the rule for nominal to actual lumber sizes?
For dry softwood: 1" boards lose 1/4" in thickness (to 3/4"), 2" to 4" thick lumber loses 1/2", widths up to 6" lose 1/2", and widths of 8" or more lose 3/4". So 2×8 = 1-1/2" × 7-1/4" and 2×12 = 1-1/2" × 11-1/4".
Is an 8 foot 2×4 actually 8 feet long?
Yes. Length is not reduced; boards are sold at their full nominal length and are often a little longer. The exception is precut studs, which are 92-5/8" so that a wall with three 1-1/2" plates is 8 ft 1-1/8" tall, ready for 8 ft drywall plus clearance.
What is the actual size of a 4×4 and a 6×6?
A 4×4 is 3-1/2" × 3-1/2" (89 × 89 mm). A 6×6 is 5-1/2" × 5-1/2" (140 × 140 mm); posts this size are usually dressed green and can shrink slightly as they dry.
What is 5/4 decking?
5/4 (five-quarter) lumber is nominally 1-1/4" thick and dresses to 1" thick. 5/4×6 deck boards are 1" × 5-1/2", often with rounded edges.
Are board feet calculated with nominal or actual size?
Softwood lumber is priced by board feet calculated from nominal dimensions: thickness × width (inches) × length (feet) ÷ 12. A 2×4 × 8 ft is 5.33 board feet, even though the actual wood volume is smaller.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.
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