🪵 Why a 2×4 Isn’t Actually 2×4
When browsing timber products, you may notice references to both Nominal Size and Finished Size. While these terms can sound confusing, the difference is straightforward — and understanding it helps you order the right timber first time.
📏 What Is Nominal Size?
The nominal size refers to the rough-sawn size of the timber before it is dried and machined.
For example:
-
2×4 timber is the nominal size
This is the size the timber starts out as, before any processing takes place.
Because timber is a natural product, it does not dry uniformly. As timber dries, it naturally loses moisture and can shrink by a few millimetres in each direction — and this amount can vary from piece to piece.
If timber were sold at its original rough size (e.g. a full 50mm × 100mm), those natural variations would make accurate planning difficult.
✂️ What Is Finished Size?
To make timber reliable and consistent, many products — especially carcassing timber — are machined to a finished size.
This means the timber is:
-
Dried
-
Planed
-
Regularised
The result is a consistent, predictable size that builders, carpenters and designers can plan around with confidence.
This is why common sizes like 2×4 have become industry standards — not because they are exact, but because everyone knows what they finish at.
🧱 So… What Size Is a 2×4?
Let’s take a common example:
-
Nominal size: 47mm × 100mm (often referred to as 2×4 or 4×2)
-
Finished size: 45mm × 95mm
In imperial terms, that finished size works out at approximately:
-
1¾″ × 3¾″
So in practice, a standard 2×4 ends up around ¼″ smaller overall once finished.
This isn’t a fault — it’s an industry standard that ensures consistency.
✅ Why Finished Size Matters
If your project relies on precise dimensions, the finished size is always the measurement that matters.
When ordering timber:
-
Use finished metric sizes as your reference
-
Treat nominal sizes as traditional naming, not exact dimensions
This avoids surprises and ensures components fit as expected.
🌲 Our Advice
At Nottage Timber Merchants:
-
Nominal sizes are used as familiar product names
-
Finished sizes are always the true working dimensions
📌 Top tip:
If final dimensions are critical, always measure and plan in metric, using the finished size.
If you’re unsure which size is right for your project, our team is always happy to help — just ask.