Calculator · Lumber & cost
Nominal to Actual Lumber Size Calculator
Compare selected North American softwood nominal labels with sourced dressed-size references or measured custom dimensions for planning and volume estimates.
Nominal vs actual size calculator
The lookup is a North American softwood-lumber reference, not a universal conversion. Actual dimensions can vary by supplier, region, species or product, moisture condition, and milling or surfacing.
Result
Select a reference size or enter measured custom dimensions, then calculate dimensions and volume.
PS 20-20 Table 3 reference rows
| Nominal | PS 20 category | Minimum dressed dry inches | Converted mm |
|---|---|---|---|
| 1x2 | Boards | 0.75 in x 1.5 in | 19 mm x 38 mm |
| 1x3 | Boards | 0.75 in x 2.5 in | 19 mm x 64 mm |
| 1x4 | Boards | 0.75 in x 3.5 in | 19 mm x 89 mm |
| 1x6 | Boards | 0.75 in x 5.5 in | 19 mm x 140 mm |
| 1x8 | Boards | 0.75 in x 7.25 in | 19 mm x 184 mm |
| 2x2 | Dimension | 1.5 in x 1.5 in | 38 mm x 38 mm |
| 2x4 | Dimension | 1.5 in x 3.5 in | 38 mm x 89 mm |
| 2x6 | Dimension | 1.5 in x 5.5 in | 38 mm x 140 mm |
| 2x8 | Dimension | 1.5 in x 7.25 in | 38 mm x 184 mm |
| 2x10 | Dimension | 1.5 in x 9.25 in | 38 mm x 235 mm |
| 2x12 | Dimension | 1.5 in x 11.25 in | 38 mm x 286 mm |
How it works
The lookup is based on minimum dressed dry sizes for selected softwood Boards and Dimension entries in the North American PS 20-20 convention. A nominal label is a product or trade designation, not a universal finished measurement.
Actual sizes can vary by supplier, region, species or product, moisture condition, and milling or surfacing. If you know the measured dimensions of your stock, enter both custom values so they override the lookup in the board-foot and volume estimate.
Metric values shown for the lookup are convenience conversions from the referenced inch dimensions, not separate metric manufacturing-standard sizes.
- Board feet = actual_thickness_inches x actual_width_inches x length_feet x quantity / 12.
- Cubic metres are estimated by converting board feet with 1 board foot approximately equal to 0.00235974 cubic metres.
Worked example
The North American PS 20-20 reference row for a dry dressed 2x4 is 1.5 inches x 3.5 inches.
Ten pieces at 8 feet long estimate as 1.5 x 3.5 x 8 x 10 / 12 = 35 board feet.
Common mistakes
- Assuming nominal sizes are universal global standards.
- Using nominal dimensions for joinery, cabinet parts, or finished layout.
- Forgetting that actual dimensions can vary by product type and supplier.
- Skipping measurement when mixing boards from different batches.
Common questions
Are these actual sizes guaranteed?
No. They are sourced minimum dressed dry reference sizes within the stated North American softwood standard. Check the product specification and measure stock when precision matters.
Why do nominal and actual dimensions differ?
Drying, surfacing, milling, species, supplier practices, and product type can all affect finished size.
Can I enter custom actual dimensions?
Yes. Custom dimensions override the reference table and should be used when you know the real stock size.
Does this replace supplier specifications?
No. Check supplier specifications and measure the material you will actually use.