Lumber size calculator: nominal vs actual
Find the size you will actually measure, or plan equal rips with room for the saw kerf.
A 2x4 actually measures
38 × 89 mm
Choose the size on the label
Minimum dressed dry softwood sizes in the US. Nominal labels stay in inches. Metric sizes are the standard's rounded values.
Source: PS 20-20, Table 3. Measure your stock before cutting; hardwood and green lumber use different sizes.
Use the actual dimensions in your plan. The length sold in feet is not reduced the same way, so measure it too.
Lumber size chart
| Nominal | Actual (in) | Actual (mm) |
|---|---|---|
| 1x2 | 3/4 x 1-1/2 | 19 x 38 |
| 1x3 | 3/4 x 2-1/2 | 19 x 64 |
| 1x4 | 3/4 x 3-1/2 | 19 x 89 |
| 1x6 | 3/4 x 5-1/2 | 19 x 140 |
| 1x8 | 3/4 x 7-1/4 | 19 x 184 |
| 1x10 | 3/4 x 9-1/4 | 19 x 235 |
| 1x12 | 3/4 x 11-1/4 | 19 x 286 |
| 2x2 | 1-1/2 x 1-1/2 | 38 x 38 |
| 2x4 · selected | 1-1/2 x 3-1/2 | 38 x 89 |
| 2x6 | 1-1/2 x 5-1/2 | 38 x 140 |
| 2x8 | 1-1/2 x 7-1/4 | 38 x 184 |
| 2x10 | 1-1/2 x 9-1/4 | 38 x 235 |
| 2x12 | 1-1/2 x 11-1/4 | 38 x 286 |
| 4x4 | 3-1/2 x 3-1/2 | 89 x 89 |
14 sizes. Selected size is highlighted.
Each of 3 equal pieces
15-3/4 in
Divide a board or sheet
Editable example: 48 in wide, three pieces, 1/8 in kerf, 1/2 in total trim. Measure the board or sheet, your blade's kerf and any edge damage.
Three pieces need two saw cuts. Each cut turns one kerf into sawdust.
Rip specifications
The rule behind the chart
Lumber is named by its size before drying and planing. For dry softwood, the US standard sets these minimum sizes:
- 1 inch nominal thickness is 3/4 inch actual. 2 inch nominal is 1-1/2 inches.
- Widths from 2 to 7 inches lose 1/2 inch: a 4 is 3-1/2 and a 6 is 5-1/2.
- Widths of 8 inches and up lose 3/4 inch: an 8 is 7-1/4 and a 12 is 11-1/4.
The first number is thickness and the second is width, both in inches. A third number, as in 2x4x8, is length in feet. Green lumber is dressed slightly larger to allow for shrinkage. Hardwood uses another system, with thickness in quarters of an inch and often random widths; measure those boards.
Allow for the saw kerf
Piece width = (measured width − total edge trim − (pieces − 1) × kerf) ÷ pieces. A 48-inch sheet with 1/2 inch of edge trim and two 1/8-inch cuts gives three pieces of 15-3/4 inches.
- Measure your sheet: stock sold as 4x8 is not always exactly 48 × 96 inches.
- Measure the gap your blade leaves in a scrap. Thin-kerf and full-kerf blades differ.
- Allow for damaged or uneven factory edges in the total trim.
- Cut and measure one piece before cutting the rest. Fractional rip results round down to the nearest 1/16 inch.
Use it with your plan
Put your parts into the cut-list calculator and check the build with the project readiness checklist. The measuring and marking guide covers reading a tape and marking a cut line you can saw to.
Sources, privacy and corrections
Sizes: Table 3 of Voluntary Product Standard PS 20-20, American Softwood Lumber Standard (minimum dressed sizes, dry). Entries are stored on this device; nothing is uploaded. Report a problem through the contact page.
Planning your first build?
The free First 5 Projects Roadmap gives you the sequence, tool list and a printable worksheet.