Many people in construction and carpentry come across terms like “16d common nails” or “8d finish nails” without knowing what the “d” actually means.
This simple letter has a long history, tying modern building practices to centuries-old methods and currency.
The use of “d” traces back to Roman times, where it signified a coin called the denarius, which later became linked to the English penny.
Over the years, this term found its way into how nails are sized and sold, with the number and “d” combination referring to a traditional way of measuring nails based on length and cost.
The system remains in use today, even as nails are now conveniently labeled by both penny size and actual length for clarity.
Nail Size Conversion Chart
The chart below shows how common nail sizes, marked by the “d” designation, relate to their lengths in inches.
This reference helps users quickly match the size they need for different construction tasks.
| Size (d) | Length (inches) |
|---|---|
| 4d | 1.5 |
| 6d | 2 |
| 8d | 2.5 |
| 10d | 3 |
| 12d | 3.25 |
| 16d | 3.5 |
| 20d | 4 |
| 30d | 4.5 |