Nail Gun Nail Sizes: 23, 18, 16 and 15 Gauge Explained

Nail guns for trim and finish work take nails sized by gauge, the thickness of the wire the nail is made from: 23, 21, 18, 16 and 15 gauge. As with wire, the higher the number the thinner the nail, so a 23 gauge pin nail is less than half the diameter of a 16 gauge finish nail. Framing nailers are different again: their nails are sold by shank diameter in inches (0.113, 0.131, 0.148 in) and by length, which line up with the penny sizes of hand-driven nails. This page gives the diameter of each gauge, what each is used for, and, from the USDA Wood Handbook’s nail equations, how well each one holds in different woods and how long it needs to be.

Nail gun gauges: diameter and uses

Gauge	Diameter (in)	Diameter (mm)	Type	Typical lengths sold	Typical uses
23 gauge	0.0258	0.66	Pin nail (headless)	3/8 to 2 in	Holding glued trim, small mouldings, veneer and craft work while the glue dries; nearly invisible holes
21 gauge	0.0317	0.81	Headed pin or micro brad	1/2 to 1-1/2 in	Thin mouldings and cabinet trim where a small head helps hold
18 gauge	0.0475	1.21	Brad nail	5/8 to 2-1/8 in	Light trim, quarter-round, cabinet backs, picture frames, small boxes
16 gauge	0.0625	1.59	Finish nail (straight)	1 to 2-1/2 in	Baseboard, door and window casing, chair rail, stair trim
15 gauge	0.0720	1.83	Finish nail (angled, DA style)	1-1/4 to 2-1/2 in	Door jambs, heavy casing and crown, exterior trim

Diameters: steel wire gauge, the gauge used for nails (the Wood Handbook’s nail tables give the same gauge-diameter pairs). Lengths and uses are typical of what is sold and how the nails are used, not a standard; check your nailer’s range.

Framing nailer nails: diameter and penny size

Shank diameter	Metric	Same diameter as (Wood Handbook)	Wire gauge
0.113 in	2.87 mm	8d box (Table 8-2)	close to 11 gauge
0.120 in	3.05 mm	—	close to 11 gauge
0.131 in	3.33 mm	8d common (Table 8-1)	close to 10 gauge
0.148 in	3.76 mm	10d and 12d common (Table 8-1)	close to 9 gauge
0.162 in	4.11 mm	16d common (Table 8-1)	close to 8 gauge

Hand-driven nail diameters from Wood Handbook Tables 8-1 (common) and 8-2 (box). 0.120 in is a common gun-nail diameter with no hand-nail equivalent. Check the code or the plans when a nail size is specified: a “16d” gun nail may be thinner than a 16d common nail.

How well each gauge holds: withdrawal per inch

The Handbook’s withdrawal equation for a smooth nail in the side grain of dry wood is p = 7,850 G^2.5 D L: holding power grows in direct proportion to the nail’s diameter D and its penetration L, and with the wood’s specific gravity G to the power 2.5. The table gives the maximum load in pounds per inch of penetration, the load at which the nail pulls out in a laboratory test. Gun nails are smooth or lightly coated shanks, so the equation is a fair guide to how they compare; the adhesive coating on many gun nails adds some initial hold that fades over time.

Wood	G (12% MC)	23 ga	21 ga	18 ga	16 ga	15 ga	0.131 in framing
Eastern white pine	0.35	15	18	27	36	41	75
SPF (Engelmann spruce)	0.35	15	18	27	36	41	75
Yellow-poplar	0.42	23	28	43	56	65	118
Douglas-fir	0.48	32	40	60	78	90	164
Red oak	0.63	64	78	117	155	178	324
Hard maple	0.63	64	78	117	155	178	324

Pounds to pull out per inch of penetration, p = 7,850 G^2.5 D (Wood Handbook Eq. 8-1b). Laboratory maximum loads, not design values. Our arithmetic.

Two things stand out. A 16 gauge finish nail is 2.4 times the diameter of a 23 gauge pin, so it holds 2.4 times as much per inch. And the wood matters more than the nail: the same nail holds 4.3 times as much in red oak as in eastern white pine. That is why pin nails are for holding parts while glue sets, not for holding anything by themselves.

How long the nail needs to be

The Handbook also says how deep a nail should go into the piece that holds its point: at least 10 times its diameter in dense woods (specific gravity over 0.61) and 14 times in light woods (under 0.42), with values in between for woods in between. The piece being nailed on should be about half that depth. The table turns that into the minimum penetration for each gauge.

Wood (holding the point)	G	Rule	23 ga	21 ga	18 ga	16 ga	15 ga
Eastern white pine	0.35	14.0 × D	0.36	0.44	0.67	0.88	1.01
SPF (Engelmann spruce)	0.35	14.0 × D	0.36	0.44	0.67	0.88	1.01
Yellow-poplar	0.42	14.0 × D	0.36	0.44	0.67	0.88	1.01
Douglas-fir	0.48	12.7 × D	0.33	0.40	0.60	0.80	0.92
Red oak	0.63	10.0 × D	0.26	0.32	0.47	0.62	0.72
Hard maple	0.63	10.0 × D	0.26	0.32	0.47	0.62	0.72

Minimum penetration in inches = multiple × nail diameter (Wood Handbook ch. 8: 10 D above G 0.61, 14 D below G 0.42, straight-line between). Add the thickness of the piece being fastened to get the nail length. Our arithmetic.

Example: 3/4 in baseboard into a pine-faced wall. In eastern white pine (G = 0.35) a 16 gauge nail needs at least 14 × 0.0625 = 0.88 in of penetration, so the nail should be at least 0.75 + 0.88 = 1.62 in long; a 2 in nail gives a margin and reaches through drywall into the stud or plate. For 1/2 in quarter-round with 18 gauge brads, 1.17 in is the minimum, so 1-1/4 in brads are a sensible choice.

Pin or finish nail? In Douglas-fir a 16 gauge nail with 1 in of penetration takes about 78 lb to pull out; a 23 gauge pin with 3/4 in of penetration about 24 lb. Glue is what makes a pinned joint strong.

Choosing a nailer

23 gauge: the holes almost disappear, and the nails rarely split thin stock. Use where glue does the holding: returns on mouldings, small trim, veneer and edge banding.
18 gauge: the general light-trim nailer. Strong enough for small mouldings and panels, with small holes to fill.
16 gauge: the standard for baseboard and casing. Longer nails reach the framing through drywall.
15 gauge: the heaviest finish nail, usually angled so it reaches into corners; for jambs, heavy casing and exterior trim.
Framing: structural nailing follows the fastener schedule in the building code (IRC Table R602.3(1) in the US) by nail type, length and diameter; check that gun nails meet it.
Hardwoods: thicker nails can split dense hardwood near an edge; the Handbook notes that blunt points and lead holes (drilled at about 90% of the shank diameter) reduce splitting, particularly in dense species. Pre-drill, or use a thinner gauge close to ends.

Frequently asked questions

What is the diameter of an 18 gauge brad nail?

0.0475 in (1.21 mm), about 3/64 in.

Is 16 gauge or 18 gauge thicker?

16 gauge is thicker: 0.0625 in against 0.0475 in for 18 gauge. A higher gauge number is a thinner nail.

What gauge are framing nails?

Framing nails are sold by diameter rather than gauge: 0.113, 0.120, 0.131, 0.148 and 0.162 in are usual. 0.131 in is about 10 gauge, the diameter of an 8d common nail.

Can I use brad nails for baseboard?

For small baseboard on a straight wall, 18 gauge brads long enough to reach the framing can work, but 16 or 15 gauge nails hold about a third to a half more per inch and are the usual choice.

How long should finish nails be?

Long enough to pass through the trim (and any drywall) and then penetrate the framing by 10 to 14 times the nail diameter; see the penetration table above. For 3/4 in trim over 1/2 in drywall, 2 in to 2-1/2 in nails are typical.

Sources and method

Diameters are the steel wire gauge values; holding power and penetration are computed from the Wood Handbook equations shown, with specific gravities from the Handbook tables. All arithmetic is ours.

USDA Forest Products Laboratory, Wood Handbook FPL-GTR-190 (2010), chapter 8: Tables 8-1 (common nails) and 8-2 (box nails) with gauge and diameter; Eq. 8-1b withdrawal; penetration of 10 to 14 diameters and side-member thickness; splitting. A US Government work.
Steel wire gauge (Washburn & Moen / US Steel Wire Gauge) diameters for gauges 8 to 23, as used for nails and published by wire makers.
International Code Council, 2021 International Residential Code, Table R602.3(1) fastener schedule (referred to, not reproduced).

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Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.