**Lumber Dimensions Explained • Nominal to Actual Chart**

**Lumber Dimensions Explained • Nominal to Actual Chart**Roof Online Staff

**Why is a Two-by-Four Called a Two-by-Four?**

Why is a two-by-four called a “two-by-four” if it’s not two inches by four inches?

Well, when a piece of lumber is first cut from the log, the board after that rough cut actually does have the approximate width and depth (the nominal lumber dimensions) by which the piece will be referred to from then on.

At that point, a two-by-four is, in fact, about two inches by four inches.

The next step in the production process is to either air-dry or kiln-dry the green lumber, in order to reduce the moisture content of the wood.

This causes the lumber to shrink as it loses its moisture volume, reducing the actual lumber dimensions. This is done to ensure that when the lumber is finished and sold its dimensions will be stable, and it won’t shrink significantly (which would change the actual lumber dimensions) after somebody uses it.

After being dried, the pieces of lumber are planed, smoothed, and have their corners rounded.

This reduces the actual lumber dimensions even further, as well as allowing the producer to be certain that the final product has the dimensions required by **industry standards.**

In the case of a two-by-four, industry standards require the finished board to be 1.5 inches by 3.5 inches).

To learn more about lumber dimensions for all sizes of boards, posts, beams, etc., see the American Softwood Lumber Standard.

**Standard Lumber Dimensions Table**

Standard American Softwood Lumber Dimensions | ||
---|---|---|

Nominal Dimensions (US – Inches) |
Actual Dimensions (US – Inches) |
Actual Dimensions (Metric) |

1 inch x 2 inch | 3/4 inch x 1-1/2 inch | 19 mm x 38 mm |

1″ x 3″ | 3/4″ x 2-1/2″ | 19 x 64 mm |

1″ x 4″ | 3/4″ x 3-1/2″ | 19 x 89 mm |

1″ x 5″ | 3/4″ x 4-1/2″ | 19 x 114 mm |

1″ x 6″ | 3/4″ x 5-1/2″ | 19 x 140 mm |

1″ x 7″ | 3/4″ x 6-1/4″ | 19 x 159 mm |

1″ x 8″ | 3/4″ x 7-1/4″ | 19 x 184 mm |

1″ x 10″ | 3/4″ x 9-1/4″ | 19 x 235 mm |

1″ x 12″ | 3/4″ x 11-1/4″ | 19 x 286 mm |

1-1/4″ x 4″ | 1″ x 3-1/2″ | 25 x 89 mm |

1-1/4″ x 6″ | 1″ x 5-1/2″ | 25 x 140 mm |

1-1/4″ x 8″ | 1″ x 7-1/4″ | 25 x 184 mm |

1-1/4″ x 10″ | 1″ x 9-1/4″ | 25 x 235 mm |

1-1/4″ x 12″ | 1″ x 11-1/4″ | 25 x 286 mm |

1-1/2″ x 4″ | 1-1/4″ x 3-1/2″ | 32 x 89 mm |

1-1/2″ x 6″ | 1-1/4″ x 5-1/2″ | 32 x 140 mm |

1-1/2″ x 8″ | 1-1/4″ x 7-1/4″ | 32 x 184 mm |

1-1/2″ x 10″ | 1-1/4″ x 9-1/4″ | 32 x 235 mm |

1-1/2″ x 12″ | 1-1/4″ x 11-1/4″ | 32 x 286 mm |

2″ x 2″ | 1-1/2″ x 1-1/2″ | 38 x 38 mm |

2″ x 3″ | 1-1/2″ x 2-1/2″ | 38 x 64 mm |

2″ x 4″ | 1-1/2″ x 3-1/2″ | 38 x 89 mm |

2″ x 6″ | 1-1/2″ x 5-1/2″ | 38 x 140 mm |

2″ x 8″ | 1-1/2″ x 7-1/4″ | 38 x 184 mm |

2″ x 10″ | 1-1/2″ x 9-1/4″ | 38 x 235 mm |

2″ x 12″ | 1-1/2″ x 11-1/4″ | 38 x 286 mm |

3″ x 3″ | 2-1/2″ x 2-1/2″ | 64 x 64 mm |

3″ x 4″ | 2-1/2″ x 3-1/2″ | 64 x 89 mm |

3″ x 6″ | 2-1/2″ x 5-1/2″ | 64 x 140 mm |

3″ x 8″ | 2-1/2″ x 7-1/4″ | 64 x 184 mm |

3″ x 10″ | 2-1/2″ x 9-1/4″ | 64 x 235 mm |

3″ x 12″ | 2-1/2″ x 11-1/4″ | 64 x 286 mm |

4″ x 4″ | 3-1/2″ x 3-1/2″ | 89 x 89 mm |

4″ x 6″ | 3-1/2″ x 5-1/2″ | 89 x 140 mm |

4″ x 8″ | 3-1/2″ x 7-1/4″ | 89 x 184 mm |

4″ x 10″ | 3-1/2″ x 9-1/4″ | 89 x 235 mm |

4″ x 12″ | 3-1/2″ x 11-1/4″ | 89 x 286 mm |

6″ x 6″ | 5-1/2″ x 5-1/2″ | 140 x 140 mm |

8″ x 8″ | 7-1/4″ x 7-1/4″ | 184 x 184 mm |

**Related Pages**

- American Softwood Lumber Standard
- Weight of a 2×4 by Wood Type and Length
- Weight of a 2×6 by Wood Type and Length
- Weight of a 2×8 by Wood Type and Length
- Weight of a 2×10 by Wood Type and Length
- Weight of a 4×4 by Wood Type and Length
- Weight of Dimensional Lumber
- Weight of Glulam and LVL
- Weight of Plywood and OSB
- Weight of Pressure-Treated Lumber
- Weight of Roofing Materials
- Weights of Various Woods Grown in the United States