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Nail Size Chart
The penny system (d) converted to nail length in inches and millimetres.
| Penny size | Length (in) | Length (mm) |
|---|
Standard: ASTM F1667 · Data checked: 2026-10-14
Frequently asked questions
What does the penny system mean?
It originated as the price per hundred nails in old English currency, and it survived as a size label long after the price stopped being 2d or 8d. The number is now purely a designation for length, and it does not scale the same way in every nail type.
Why is a 16d nail not twice a 8d nail?
Because the designation tracks length loosely and differently by type — common, box, and finishing nails all step differently. A 16d common nail is 3.5 in, an 8d common is 2.5 in, so the range is much tighter than the numbers suggest.
What is the difference between common and box nails?
Common nails have a larger shank diameter for the same length and are used for structural framing. Box nails are thinner, which is why they are less likely to split thinner timber, and they are used for lighter work. Substituting box for common in framing is a strength reduction.
Can I use any nail outdoors?
Only if it is galvanised, stainless or otherwise coated. Plain steel nails will rust and stain the timber around them, and in treated timber the corrosion can be fast enough to affect the joint. Use hot-dip galvanised or stainless for exterior and treated work.