# Lumber Nominal vs. Actual Size Chart

> Compare common North American nominal lumber labels with typical surfaced dimensions and understand which dimensions belong in volume, weight and layout calculations.

- Canonical URL: https://buildmeter.net/guides/lumber-nominal-vs-actual-size-chart/
- Category: Structures & Carpentry
- Author: Liron Elimeleh
- Publisher: BuildMeter, developed by ELStudios
- Published: July 19, 2026
- Last reviewed: July 19, 2026

## Direct answer

Nominal lumber names describe the trade size, while surfaced lumber is smaller after drying and planing. For example, a nominal 2 × 4 is commonly about 1.5 × 3.5 inches. Use actual measured dimensions for volume, fit and metric conversion, and nominal names for purchasing and specification references.

## Primary calculator

- [Lumber Board-Foot Calculator](https://buildmeter.net/lumber-board-foot-calculator/)

## Nominal names and physical dimensions serve different purposes

North American lumber is commonly sold by nominal trade names such as 2 × 4 or 4 × 4. Surfacing and drying reduce the finished cross-section. The trade name helps identify the product category, while actual dimensions determine fit, physical volume, weight and converted metric size.

### Common surfaced softwood dimensions

| Nominal size | Typical actual size | Approximate metric actual size |
| --- | --- | --- |
| 1 × 2 | 3/4 × 1-1/2 in. | 19 × 38 mm |
| 1 × 4 | 3/4 × 3-1/2 in. | 19 × 89 mm |
| 1 × 6 | 3/4 × 5-1/2 in. | 19 × 140 mm |
| 1 × 8 | 3/4 × 7-1/4 in. | 19 × 184 mm |
| 2 × 2 | 1-1/2 × 1-1/2 in. | 38 × 38 mm |
| 2 × 4 | 1-1/2 × 3-1/2 in. | 38 × 89 mm |
| 2 × 6 | 1-1/2 × 5-1/2 in. | 38 × 140 mm |
| 2 × 8 | 1-1/2 × 7-1/4 in. | 38 × 184 mm |
| 2 × 10 | 1-1/2 × 9-1/4 in. | 38 × 235 mm |
| 2 × 12 | 1-1/2 × 11-1/4 in. | 38 × 286 mm |
| 4 × 4 | 3-1/2 × 3-1/2 in. | 89 × 89 mm |
| 6 × 6 | 5-1/2 × 5-1/2 in. | 140 × 140 mm |
The table reflects common surfaced dimensions, not every product. Rough-sawn lumber, heavy timber, decking, specialty boards and regional products can differ. Measure the actual stock or use the grade stamp and supplier data when fit is critical.

## Which dimensions belong in which calculation?

### Choose nominal or actual dimensions by task

| Task | Dimension to use | Reason |
| --- | --- | --- |
| Physical volume and weight | Actual dimensions | The wood occupies the surfaced cross-section. |
| Opening, notch or connector fit | Actual measured dimensions | Clearance depends on physical size and tolerance. |
| Purchasing list | Nominal trade name plus length and grade | Suppliers identify common framing lumber by nominal size. |
| Metric conversion | Actual dimensions | AWC advises converting physical dimensions rather than treating the nominal label as exact inches. |
| Structural capacity | Project specification and design values | Species, grade, size, moisture and use all matter. |

## Worked volume example

A nominal 2 × 4 that is actually 1.5 × 3.5 in. and 8 ft long has a physical volume of 1.5 × 3.5 × 96 = 504 in³, or 0.292 ft³. Using the nominal 2 × 4 cross-section would produce 768 in³ and overstate physical volume by more than 50%.

## Board feet require context

A board foot is 144 in³. Traditional lumber transactions may refer to rough or nominal conventions, while a physical-volume calculation uses actual thickness and width. Confirm whether a supplier’s board-foot pricing is based on nominal or surfaced dimensions before comparing it with a calculator.

## Common mistakes

- Converting “2 × 4” directly to 50.8 × 101.6 mm as though it were a physical finished size.
- Using actual dimensions in a shopping list without also naming the nominal product.
- Assuming pressure-treated, rough-sawn and kiln-dried stock share identical dimensions.
- Using size alone to infer structural capacity.
- Forgetting that length can also be slightly different from the nominal or ordered value.

## Use the calculators

Enter the appropriate dimensions in the [Lumber Board-Foot Calculator](https://buildmeter.net/lumber-board-foot-calculator/) and use actual cross-section plus density in the [Lumber Weight Calculator](https://buildmeter.net/lumber-weight-calculator/). Framing quantities can be developed with the [Stud Wall Framing Calculator](https://buildmeter.net/stud-wall-framing-calculator/).

## Sources and limitations

- [American Wood Council — weights and measurement](https://awc.org/priorities/codes-standards/weights-measurement/)
- [American Wood Council — metric lumber conversion FAQ](https://awc.org/faq/how-do-i-convert-to-metric-lumber-sizes/)
- [NIST SI units — length](https://www.nist.gov/pml/owm/si-units-length)

Structural lumber selection must account for species, grade, treatment, moisture, span, load, connections and applicable design requirements. This chart is a dimension reference, not a span or capacity table.

## Related calculators

- [Lumber Weight Calculator](https://buildmeter.net/lumber-weight-calculator/)
- [Stud Wall Framing Calculator](https://buildmeter.net/stud-wall-framing-calculator/)
- [Wall Plate Lumber Calculator](https://buildmeter.net/wall-plate-lumber-calculator/)

## Related guides

- [How to Measure a Roof from the Ground](https://buildmeter.net/guides/how-to-measure-a-roof-from-the-ground/)
- [Roof Pitch Multiplier Chart](https://buildmeter.net/guides/roof-pitch-multiplier-chart/)