Nail Size Converter
Convert nail penny sizes (2d to 60d) to length in inches and mm with gauge and use case.
Covers framing (16d = 3.5 in), finish, roofing, and brad nails.
Select a penny size — see the nail length and typical use.
Nail sizes are measured in “penny” (d) — an old English system.
The “d” in nail sizes stands for “denarius” (a Roman coin). Originally, it was the cost in pennies for 100 nails.
Common nail sizes:
| Penny | Length (in) | Length (mm) | Common Use |
|---|---|---|---|
| 2d | 1.00 | 25.4 | Small trim, crafts |
| 3d | 1.25 | 31.8 | Light trim |
| 4d | 1.50 | 38.1 | Small trim, shingles |
| 6d | 2.00 | 50.8 | Siding, light framing |
| 8d | 2.50 | 63.5 | Sheathing, subflooring |
| 10d | 3.00 | 76.2 | General framing |
| 12d | 3.25 | 82.6 | Framing, sheathing |
| 16d | 3.50 | 88.9 | Wall framing (most common) |
| 20d | 4.00 | 101.6 | Heavy framing |
| 30d | 4.50 | 114.3 | Heavy structural |
| 40d | 5.00 | 127.0 | Very heavy structural |
| 60d | 6.00 | 152.4 | Timber framing |
The practical catch with the penny number is what it does and doesn’t tell you. It sets the length only, not the thickness. An 8d nail is always about 2.5 inches long, yet its gauge (diameter) varies between common, box, and finish styles, which are made thicker or thinner for different jobs.
So “8d” tells you how deep the nail reaches but not how much it will split the wood or how well it will hold. Common nails are thick and strong for framing; box nails are thinner to reduce splitting in lighter stock; finish nails are thin with a tiny head meant to be hidden in trim. Choosing the right type matters as much as the length, which is why a framing nailer and a finish nailer take completely different nails even at the same penny size.
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This converter runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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