Nail Gauge Size Chart: Gauge, Diameter and Real Holding Power by Job
Gauge runs backwards: 23 gauge is a 0.025 in pin, 15 gauge is a 0.072 in nail almost three times thicker. Use 18 gauge for trim under 3/4 in, 16 gauge for 3/4 in baseboard and casing, 15 gauge when the fastener has to cross drywall into a stud, and 23 gauge anywhere the wood will split.
Gauge is wire gauge, so the numbers run backwards. A 23 gauge pin is 0.025 in thick. A 15 gauge finish nail is 0.072 in, nearly three times the diameter and roughly eight times the cross-sectional area.
The short version: 18 gauge brads for trim under 3/4 in thick and for cabinet assembly, 16 gauge finish nails for 3/4 in baseboard and casing, 15 gauge when the nail has to pass through drywall and still bite an inch of stud, 23 gauge headless pins for mitre returns and anything you expect to split. Framing nailers are a separate species and start at 0.113 in shank.
The holding-power figures in the chart below are not marketing numbers. They are calculated from the standard withdrawal formula the timber engineering codes use, so you can check the arithmetic yourself and apply it to any species you like.
Every gauge, with the numbers that decide the job
Withdrawal resistance is given per inch of penetration into the holding member, which is the piece the nail ends up gripping, not the piece it passes through. A 2 in 16 gauge nail through 3/4 in of casing has 1 1/4 in of penetration, so multiply the table figure by 1.25.
Two caveats before you read it. These are smooth-shank values, and they are design values rather than ultimate failure loads, so the actual pull-out is higher but the margin is what keeps trim on the wall in year ten. And withdrawal is only one failure mode: a headless 23 gauge pin has essentially no head, so it can also simply pull through the workpiece face.
Gauge Shank diameter Head Length range Withdrawal in SPF (lb per in of penetration) Withdrawal in red oak Where it belongs 23 ga pin 0.025 in (0.64 mm) Headless or micro head 3/8 to 2 in 3.9 13.2 Mitre returns, small mouldings, holding parts while glue cures 21 ga pin 0.033 in (0.84 mm) Slight head 1/2 to 1 3/8 in 5.2 17.4 A compromise almost nobody needs; skip it 18 ga brad 0.0475 in (1.2 mm) Small chisel head 5/8 to 2 1/8 in 7.5 25.0 Trim under 3/4 in, cabinet backs, drawer bottoms, shoe mould 16 ga finish 0.0625 in (1.6 mm) Proper finish head 3/4 to 2 1/2 in 9.9 32.9 3/4 in baseboard, casing, face frames, jamb work 15 ga angled finish 0.072 in (1.8 mm) Full finish head, DA or FN collation 1 1/4 to 2 1/2 in 11.4 37.9 Door jambs, thick casing, crown into blocking, exterior trim 14 ga 0.080 in (2.0 mm) Finish head 1 1/2 to 2 1/2 in 12.6 42.1 Uncommon; heavy stair parts and thick mouldings Framing, 0.113 in shank 0.113 in (2.9 mm) Full round or clipped 2 to 3 1/4 in 17.8 59.5 Sheathing, light framing, shop wall studs Framing, 0.131 in shank 0.131 in (3.3 mm) Full round or clipped 2 3/8 to 3 1/2 in 20.7 68.9 Structural framing, workbench bases, shop fixtures Multiply the withdrawal column by your actual penetration depth in inches to get the design hold per nail, then decide how many nails the job needs. Figures come from the standard W = 1380 x G^2.5 x D relationship, using G = 0.42 for SPF and G = 0.68 for red oak. Notice what the oak column does. The same 18 gauge brad holds better than three times as well in red oak as in SPF, which is why people who only ever nail pine develop instincts that fall apart the first time they trim out a hardwood library.
Notice also that framing nails are quoted by shank diameter, not gauge. Nobody in the trade says 10 gauge framing nail; they say a 0.131. Two different framing nailers can both take 3 1/4 in nails and want different diameters, and using the wrong one jams the tool.
Where the 16 versus 18 gauge decision actually changes the outcome
Most of the time either works and the argument is theology. There are four cases where it genuinely is not.
Thin stock near an end. A 16 gauge nail into the last inch of a 1/2 in thick oak return will split it, most of the time, no matter how carefully you set the depth. The 0.0475 in brad might get away with it. The 0.025 in pin will.
Trim that has to cross drywall. If the fastener passes through 1/2 in of drywall on its way to a stud, an 18 gauge brad in 2 in length leaves only about 3/4 in of penetration and it is holding into a stud with a hole punched through soft gypsum around it. That is the 15 gauge case, or a 2 1/2 in 16 gauge at minimum.
Anything carrying weight. A shelf cleat, a hanging rail, a face frame that will take a door: the finish nail is holding the assembly while the glue cures and the glue does the work afterwards. But if there is no glue in the joint, the gauge is the joint.
Painted versus stained. A 15 gauge head leaves a hole you will fill; a 23 gauge pin leaves one you can often ignore under a clear finish. On stained trim that difference decides the gauge before anything structural does.
Length lookup by what you are actually fastening
The rule is simple arithmetic. Add up everything the nail passes through, add the penetration you want in the holding member, round up to the next stock length. The only judgement call is the penetration figure, and the trade convention is 1 in into a stud and 1/2 to 3/4 in into wood-to-wood joinery.
What you are fastening Material thickness What is behind it Penetration wanted Nail length Gauge Quarter round or shoe over baseboard 1/2 in 3/4 in baseboard only 1/2 in 1 1/4 in 18 ga Panel moulding onto a face frame 1/4 in 3/4 in frame stock 3/4 in 1 in 23 or 18 ga Baseboard over drywall into a stud 3/4 in Stud behind 1/2 in drywall 1 in 2 1/2 in 16 or 15 ga Casing onto a jamb, no drywall between 3/4 in 3/4 in jamb 3/4 in 1 1/2 to 2 in 16 ga Casing into the trimmer through drywall 3/4 in Stud behind 1/2 in drywall 1 in 2 1/2 in 15 ga Crown into ceiling blocking 9/16 in Blocking behind 1/2 in drywall 1 in 2 1/4 to 2 1/2 in 15 or 16 ga Face frame onto a plywood carcass edge 3/4 in frame 3/4 in plywood edge 1/2 to 5/8 in 1 1/4 in 18 ga Ply back into a rabbet 1/4 in 3/8 in of rabbet shoulder 1/4 to 3/8 in 5/8 to 3/4 in 18 or 23 ga Drawer box, tacking a rabbet while glue sets 1/2 in side 1/2 in front 1/2 in 1 in 18 ga Mitre return on a 3/4 in cap 3/4 in 3/4 in end grain 1/2 in 1 in 23 ga only Work down the row: thickness plus anything in the path plus penetration, rounded up. Buy the two lengths you use most in bulk rather than a strip pack of six. Splitting is a function of the head and the end grain
A nail splits wood by wedging fibres apart. Two things drive it: the volume of steel you are forcing in, and how close you are to a free end where the fibres have somewhere to go.
Within 2 in of the end of a hardwood board, drop a gauge. Within 1 in, drop two. A 3/4 in white oak plinth block that took a 16 gauge nail happily in the middle will crack from a nail 3/4 in from the end, every time, and the split usually appears an hour later when nobody is watching.
Angling the nail 5 to 10 degrees off perpendicular helps more than people expect. It moves the wedge across more fibres instead of straight down one line, and it improves withdrawal by a little as a bonus.
For anything genuinely brittle, wenge and some quartersawn oak included, a 23 gauge pin plus glue beats a 16 gauge nail with no glue. The pin is holding the part still, not holding the joint.
Straight or angled magazine
16 gauge comes both ways. Straight-magazine nailers are cheaper and the collation is easier to find, and they are perfectly fine on flat runs of baseboard.
Angled tools, whether 15 or 16 gauge, get into inside corners and up under crown where a straight magazine simply will not physically fit. If you only own one finish nailer and you do any built-in work, the angled tool is the one that earns its shelf.
15 gauge is only ever angled, and the two collation systems are not interchangeable. DA collation runs at 34 degrees, FN at 33 or 34 depending on brand, and a strip of the wrong one will not seat. Check which your tool takes before you buy a case.
Drive pressure at the tool, and how to set it
None of this is about sizing a compressor. This is the pressure showing on the regulator at the tool's own inlet, which is the only number that changes how the nail sets.
Start low. Fire into an offcut of the same species and thickness, and raise 5 psi at a time until the head sits about 1/32 in below the surface. Too much pressure blows the head through in softwood and leaves a crater you have to fill twice; too little proud-sets the nail and you end up tapping heads by hand for an hour.
Gauge Fastener length Pine and poplar, starting psi Oak and maple, starting psi What a correct set looks like 23 ga 1 in 60 to 70 75 to 90 Pin just below flush, no visible dimple 23 ga 2 in 80 to 90 95 to 110 Pin below flush; longer pins wander in figured grain 18 ga 1 1/4 in 70 to 80 85 to 95 Head 1/32 in below, clean round hole 18 ga 2 in 85 to 95 100 to 110 Head 1/32 in below, no surface crush ring 16 ga 2 in 80 to 90 95 to 110 Head 1/32 in below, no tear-out around the hole 16 ga 2 1/2 in 90 to 100 105 to 120 Head 1/32 in below; watch for deflection in hard grain 15 ga 2 1/2 in 90 to 100 110 to 120 Head 1/32 to 1/16 in below, ready to fill Framing, 0.131 in 3 1/4 in 100 to 110 Not applicable Head flush with the sheathing face, never sunk Use this as a starting point, then set the tool's own depth adjuster rather than chasing the regulator. Most finish nailers are rated 70 to 120 psi; if you are outside that window to get a clean set, something else is wrong. Long nails deflect. A 2 1/2 in 15 gauge nail entering hard grain at an angle can curve and emerge out the face of the trim eight inches away, which is a spectacular way to ruin a length of casing. If you feel the tool kick oddly, stop and look before you fire the next one.
The nail is not the joint
On cabinet work, treat every brad as a clamp. Glue does the holding; the fastener stops the part sliding while the glue grabs, which is a job a 0.0475 in brad does superbly and a 0.072 in nail does no better while splitting more stock.
On trim, the opposite is true. There is rarely glue in a baseboard-to-stud connection, so the nail is the entire mechanical system and the gauge and penetration figures in the first table are what is holding your skirting to the wall in ten years' time.
Knowing which of those two situations you are in decides the gauge faster than any chart does.