About the Nail Size Converter
This nail size converter translates the old penny system (written 8d, 10d, 16d) into the numbers you actually need: length in inches and millimeters, wire gauge, and shank diameter. Pick common or box nails and a penny size to see the full specification and an approximate count per pound, along with a chart of every size of that type.
It is handy when a plan, code table or fastening schedule calls for a penny size but the box at the store lists only length and diameter, or when you are buying collated nails for a framing nailer, which are sold by length and shank diameter (for example 3-1/4 in × 0.131 in).
Dimensions come from the US Forest Products Laboratory Wood Handbook tables for bright common wire nails and smooth box nails. Box nails have the same length as common nails of the same penny size but a thinner shank; sinkers and coated nails are typically about 1/8 inch shorter and thinner still. Nails per pound are estimated from shank volume and steel density, so treat them as approximate.
With the default inputs, the length is 3.5 in. Change any value above to recalculate instantly.
How to use the nail size converter
- 1Choose common or box nails.
- 2Pick the penny size from your plan or fastening schedule.
- 3Read the length, diameter and gauge.
- 4Use length × diameter to match collated nailer nails.
- 5Check the chart below to compare neighbouring sizes.
Formula and method
Lengths, gauges and diameters are looked up from the Wood Handbook tables for bright common wire nails and smooth box nails; they are not calculated from the penny number, because the system is a historical naming convention. For 2d to 10d nails the length does follow a rule of thumb — one quarter of the penny number plus half an inch — but larger sizes step irregularly.
Metric values use the exact conversion 1 inch = 25.4 mm. The nails-per-pound estimate treats the nail as a steel cylinder of the listed length and diameter (steel ≈ 0.2836 lb per cubic inch) and ignores the head and point, which roughly cancel; real counts vary by manufacturer and coating.
- L
- Nail length (in)
- d
- Shank diameter (in)
Worked examples
16d common nail
A 16d common nail is 3-1/2 inches (88.9 mm) long with a 0.162 inch (8 gauge) shank. As a steel cylinder that is about 0.0205 lb, or roughly 49 nails per pound.
8d common nail
An 8d common is 2-1/2 inches (63.5 mm) by 0.131 inch, about 10¼ gauge — roughly 105 per pound.
8d box nail
An 8d box nail has the same 2-1/2 inch length as the common nail but a thinner 0.113 inch shank (11½ gauge), so there are about 141 per pound.
Frequently asked questions
How long is a 16d nail?+
A 16d nail is 3-1/2 inches (88.9 mm) long. The common version has a 0.162 inch shank, the box version 0.135 inch. Cement-coated sinkers sold as 16d are slightly shorter and thinner than common nails.
What does the "d" in nail sizes mean?+
The "d" stands for penny, from the Roman coin denarius. It originally referred to the price of a hundred nails in old English pennies and survives today only as a length designation.
What is the difference between common and box nails?+
They have the same length for a given penny size, but box nails have a thinner shank. They are less likely to split thin or dry wood but have lower withdrawal and shear strength than common nails.
What size nail is used for framing?+
Wall framing commonly uses 16d nails (3-1/2 in) for face-nailing plates and 8d or 10d nails for toenailing, though exact sizes come from the fastening schedule in your building code, such as IRC Table R602.3(1).
What gauge is an 8d nail?+
An 8d common nail is about 10¼ gauge (0.131 in diameter), while an 8d box nail is about 11½ gauge (0.113 in). Smaller gauge numbers mean thicker wire.