Nominal vs Actual Lumber Size Calculator
Compare volumes using editable nominal and actual lumber dimensions.
Calculations run locally in your browser. Inputs are not transmitted or attached to analytics.
Common dressed softwood reference sizes
This compact reference reflects common dry dressed US softwood dimensions associated with the current NIST PS 20 standard context. It is a lookup aid, not an automatic substitution rule. Supplier tolerances, moisture, surfacing and product category can change measured size; rough hardwood and specialty stock use different conventions. Measure the actual piece whenever the transaction depends on physical volume.
| Nominal inches | Common actual inches |
|---|---|
| 1 × 4 | ¾ × 3½ |
| 1 × 6 | ¾ × 5½ |
| 1 × 8 | ¾ × 7¼ |
| 1 × 10 | ¾ × 9¼ |
| 1 × 12 | ¾ × 11¼ |
| 2 × 4 | 1½ × 3½ |
| 2 × 6 | 1½ × 5½ |
| 2 × 8 | 1½ × 7¼ |
| 2 × 10 | 1½ × 9¼ |
| 2 × 12 | 1½ × 11¼ |
Compare two explicitly entered cross-sections
The comparison tool calculates one volume from nominal thickness and width and another from actual thickness and width while holding length and quantity constant. Both dimension sets remain editable. The result reports actual volume, nominal volume, the signed BF difference and percentage difference relative to nominal volume.
A negative difference means the measured actual cross-section contains less geometric volume than the nominal labels imply. It does not prove an invoice is wrong; the transaction may intentionally use an industry tally convention.
Worked 2 × 6 comparison
One eight-foot piece entered as nominal 2 × 6 contains 8 nominal BF. Entered as actual 1.5 × 5.5, the same length contains 5.5 physical BF. The difference is −2.5 BF, or −31.25% relative to the nominal calculation. The tool shows both rather than replacing one silently.
Reference sizes are not universal substitutions
The accompanying common dressed softwood table is a lookup aid associated with US softwood practice. It does not automatically describe rough hardwood, green lumber, reclaimed stock, specialty milling or every tolerance. Measure the product or use the supplier specification when physical dimensions matter.
Choosing the comparison basis
Use identical length and quantity for a clean cross-section comparison. Record moisture and surfacing state if those facts explain the difference. When reviewing a purchase, preserve the seller’s original nominal tally separately from any actual-volume calculation so the audit trail does not rewrite the transaction.
Questions about this topic
Does the calculator know every actual size?
No. Defaults are editable references; measured or documented values control the comparison.
Why is the percentage based on nominal volume?
It expresses actual-minus-nominal as a share of the nominal reference.
Can actual volume be larger?
Yes, especially with rough or oversized stock; the signed difference will be positive.
Related BoardFoot Bench pages
Method and content reviewed 3 September 2026.