Understanding Nominal vs. Finished Timber Sizes in the UK
What Are Nominal and Finished Timber Sizes?
In the UK timber industry, wood is commonly sold using two different size measurements:
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Nominal Size – The size stated when purchasing timber represents the dimensions before processing.
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Finished Size – The actual size of the timber after it has been planed and sanded to create a smoother surface.
Why Is There a Difference?
Timber is initially cut to its nominal size, but once it undergoes planing and sanding, a small portion of the wood is removed. This reduction ensures that the timber has a smooth and uniform finish, making it more suitable for construction and carpentry projects.
Generally, planing reduces the thickness and width by approximately 2mm on the height and up to 5mm on the width, depending on the type of timber and processing method.
Common Nominal vs. Finished Timber Sizes
Here are some examples of how nominal sizes compare to their finished sizes:
| Nominal Size (mm) | Finished Size (mm) |
|---|---|
| 47 x 100 | 45 x 95 |
| 47 x 75 | 45 x 70 |
| 75 x 150 | 70 x 145 |
| 50 x 225 | 47 x 220 |
How to Choose the Right Size
When selecting timber, it’s crucial to check the finished size to ensure it meets your project requirements. Many suppliers list both sizes, but if unsure, always ask for clarification.
Key Takeaways
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Nominal sizes refer to the rough-sawn timber before finishing.
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Finished sizes are the actual dimensions you receive after processing.
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Typically, planing reduces 2mm in height and up to 5mm in width.
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Always verify both sizes when purchasing to ensure suitability for your project.