What does the d mean in 16d nails?

It stands for denarius, a Roman coin. The penny size was originally the price per hundred nails in medieval England, so a 16d nail cost sixteen pence per hundred. Prices changed and the nail sizes were standardised, so the designation survived as a name with no arithmetic meaning — there is no formula relating the penny number to the length or diameter.

How long is an 8d nail?

2.5 in, or 63.5 mm, with a 0.131 in (3.3 mm) shank diameter in the common nail series. It is the general-purpose framing nail for studs, sheathing and decking. A 16d is 3.5 in (89 mm) with a 0.162 in shank and is the heavy framing nail for joists and rafters.

Is a box nail the same as a common nail?

No — a box nail has a smaller shank diameter than a common nail at the same penny size. A 16d common nail is 0.162 in; a 16d box nail is about 0.148 in, roughly 9% thinner. Box nails are less likely to split thin or dry lumber, but they also hold less. A specification that says "16d nail" without naming the type is ambiguous, and the difference matters in structural work.

How much of the nail should penetrate?

Framing practice is that the nail should penetrate the member being held by at least half its length. The reason is that the nail's grip comes from the shank in the lower member — the part passing through the upper member contributes almost nothing. Driving into end grain reduces holding power further, to roughly two-thirds of the cross-grain value, which is why joints in end grain get extra nails.

Do galvanised nails have different dimensions?

Electroplated galvanised nails are within a few thousandths of an inch of the bare size. Hot-dip galvanised nails have a much thicker coating — typically 0.0015 to 0.0025 in per surface — so the installed diameter is noticeably larger. That can be enough to split hardwood or thin stock that the bare nail would have entered cleanly, and it is why hot-dip nails are specified by their coating class as well as their size.

Nail Size Chart

Common wire nail sizes from 2d to 60d — penny size against length and shank diameter in inches and millimetres, with the typical use for each.

Data verified 2026-09-29 · based on ASTM F1667-22

Quick Answer

The penny size is not a length and not a diameter — it is a historical price designation that survived as a name. An 8d nail is 2.5 in (64 mm) long with a 0.131 in (3.3 mm) shank, and a 16d is 3.5 in (89 mm) with a 0.162 in shank. Length rises by 1/2 in per step up to 10d, then more slowly, while diameter keeps climbing.

Find a nail size

Common Wire Nail Sizes

Penny size^[1]	Length in^[1]	Shank diameter in^[1]	Length mm^[2]	Shank diameter mm^[2]	Typical use^[1]
2d #	1.00	0.0720	25.4	1.83	Small trim and moulding
3d #	1.25	0.0800	31.8	2.03	Light trim, cabinet backs
4d #	1.50	0.0990	38.1	2.51	Trim, small casing
5d #	1.75	0.1010	44.4	2.57	Casing and baseboard
6d #	2.00	0.1130	50.8	2.87	General framing for light members, fencing
7d #	2.25	0.1130	57.1	2.87	Interior trim, sheathing
8d #	2.50	0.1310	63.5	3.33	The general-purpose framing nail — studs, sheathing, decking
9d #	2.75	0.1310	69.8	3.33	Interior framing
10d #	3.00	0.1480	76.2	3.76	Framing, subflooring
12d #	3.25	0.1480	82.5	3.76	Framing and decking
16d #	3.50	0.1620	88.9	4.11	The heavy framing nail — joists, rafters, headers
20d #	4.00	0.1920	101.6	4.88	Heavy framing, deck framing
30d #	4.50	0.2070	114.3	5.26	Timber and pole construction
40d #	5.00	0.2250	127.0	5.71	Heavy timber, marine construction
50d #	5.50	0.2440	139.7	6.20	Heavy timber and cribbing
60d #	6.00	0.2620	152.4	6.65	Heavy timber and cribbing

Dimensions are for common wire nails, the general-purpose round nail. Other nail types share the penny-size names but not the dimensions: box nails are thinner than common nails at the same penny size (a 16d box is 0.148 in against the common 0.162), and finishing, casing, roofing and duplex nails each have their own shank sizes. Always confirm which type a specification means — "16d nail" is ambiguous and the difference in shank diameter is about 10%.

What a Penny Size Actually Means

The "d" in 8d stands for denarius, a Roman silver coin. The penny size was originally the price of one hundred nails of that size in medieval England — a hundred 2d nails cost twopence. The sizes were standardised and the prices were not, so the system survived as a naming convention with no arithmetic content at all.

That is why there is no formula. The penny number is a label, and the relationship between the number and the dimensions is historical. Some regularities exist — from 2d to 10d each 2 penny steps adds 1/2 in of length — but the pattern breaks at 12d and changes again at 16d, and the diameter does not follow the same steps as the length at all. Anyone who tries to compute a nail length from its penny size will be wrong.

The practical consequence is that penny sizes must be looked up. The two that matter most in framing are 8d and 16d: 8d for sheathing, studs and general work, and 16d for joists, rafters and headers. A framing specification is often written entirely in those two sizes.

Nail Length, Diameter and Holding Power

Holding power in wood comes mostly from the shank diameter and the length of shank in the lower member, not from the length overall. A nail's withdrawal resistance is roughly proportional to the diameter raised to a power and to the depth of penetration into the piece being held.

The traditional rule for framing is that the nail should penetrate the member being held by at least half its length, and that a nail driven into end grain — as when nailing a stud to a plate — holds only about two-thirds as well as one driven across the grain. That is why framing practice uses two nails per joint rather than one longer nail: the second nail adds more capacity than extra length on the first.

Diameter matters more than most people expect. Going from an 8d (0.131 in) to a 16d (0.162 in) is a 24% increase in diameter and roughly a 50% increase in cross-section, which translates into a large gain in both holding power and shear strength. That is the real reason a framer reaches for the bigger nail on a structural joint, not the extra inch of length.

Note also that nails are sized by shank diameter before galvanising. A hot-dip galvanised nail is thicker than its nominal figure by the coating thickness, which can be enough to split a thin piece of hardwood that the bare nail would have entered cleanly.

Frequently Asked Questions

What does the d mean in 16d nails?: It stands for denarius, a Roman coin. The penny size was originally the price per hundred nails in medieval England, so a 16d nail cost sixteen pence per hundred. Prices changed and the nail sizes were standardised, so the designation survived as a name with no arithmetic meaning — there is no formula relating the penny number to the length or diameter.
How long is an 8d nail?: 2.5 in, or 63.5 mm, with a 0.131 in (3.3 mm) shank diameter in the common nail series. It is the general-purpose framing nail for studs, sheathing and decking. A 16d is 3.5 in (89 mm) with a 0.162 in shank and is the heavy framing nail for joists and rafters.
Is a box nail the same as a common nail?: No — a box nail has a smaller shank diameter than a common nail at the same penny size. A 16d common nail is 0.162 in; a 16d box nail is about 0.148 in, roughly 9% thinner. Box nails are less likely to split thin or dry lumber, but they also hold less. A specification that says "16d nail" without naming the type is ambiguous, and the difference matters in structural work.
How much of the nail should penetrate?: Framing practice is that the nail should penetrate the member being held by at least half its length. The reason is that the nail's grip comes from the shank in the lower member — the part passing through the upper member contributes almost nothing. Driving into end grain reduces holding power further, to roughly two-thirds of the cross-grain value, which is why joints in end grain get extra nails.
Do galvanised nails have different dimensions?: Electroplated galvanised nails are within a few thousandths of an inch of the bare size. Hot-dip galvanised nails have a much thicker coating — typically 0.0015 to 0.0025 in per surface — so the installed diameter is noticeably larger. That can be enough to split hardwood or thin stock that the bare nail would have entered cleanly, and it is why hot-dip nails are specified by their coating class as well as their size.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	ASTM F1667 — Driven Fasteners: Nails, Spikes and Staples	standard	ASTM F1667-22
[2]	Value computed from the standard's defining relationship	derived	Computed at build time from the defining formula stated on the page and verified against every row, then checked against known standard values held as anchors. Nothing in this column was transcribed.

Data Sources

Standard	Revision	What it covers on this page
ASTM F1667 — Driven Fasteners: Nails, Spikes and Staples	ASTM F1667-22	the common nail dimensions, penny sizes and shank diameters
ASME B18.27 — Tapered and Reduced Section Headed Fasteners	n/a — withdrawn; the nail standard is now ASTM F1667	historical nail dimension definitions
NIST Handbook 44 — Specifications, Tolerances and Other Technical Requirements	NIST Handbook 44, 2024 edition	the retail sale requirements for nails sold by size

Cross-checked against:

Lengths and shank diameters cross-checked against two manufacturers' published common-nail tables
Penny-size to length progression verified against the standard series, including the two places where the step changes
Three sizes held as known-value checks across the series — 8d, 10d and 16d
Millimetre conversions recomputed at build time for every row

Derived values — the following values on this page are calculated, not taken directly from the standard:

Value	How it is derived
Length and shank diameter in millimetres	Inch dimension × 25.4, recomputed at build time for every row. 2.50 in is held as a known-value check at 63.5 mm.

Dimensions are for common wire nails. Box, casing, finishing, roofing, duplex and screw-shank nails share penny-size names but have different shank diameters — a 16d box nail is about 9% thinner than a 16d common nail. Shank diameters are before coating; hot-dip galvanised nails are noticeably thicker in service. Confirm the nail type, not just the penny size, before specifying.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "Nail Size Chart." https://refmanual.com/charts/nail-sizes/ (accessed 2026-09-29). Data from ASTM F1667 — Driven Fasteners: Nails, Spikes and Staples, ASTM F1667-22.

BibTeX

@misc{nail-sizes,
  title        = {Nail Size Chart},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/nail-sizes/}},
  note         = {Accessed: 2026-09-29},
  source       = {ASTM F1667 — Driven Fasteners: Nails, Spikes and Staples, ASTM F1667-22}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Nail Size Chart
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/nail-sizes/
PY  - 2026
DA  - 2026-09-29
N1  - Source: ASTM F1667 — Driven Fasteners: Nails, Spikes and Staples, ASTM F1667-22
ER  -

Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.