Add the trim, any drywall or substrate, and how much you want in the stud. That sum is the minimum. The calculator then rounds up to a common 18-gauge brad or 16-gauge finish size. Wood-to-wood sets substrate to zero. Layout and stock pick only — not a shear rating.
Use it when nailing trim, casing or baseboard through drywall into framing. Add the trim thickness, the drywall or other substrate, and the penetration you want into the stud, and the page suggests the nail length and the nearest common size for your gauge.
It is the quick way to avoid nails that only grab the drywall, or long nails that poke through a thin stop or the back of a cabinet.
A brad has to pass through everything in front of the stud and still bite the framing. The minimum length is the sum of those three numbers. Then pick the shortest nail on the gun’s common-size list that is at least that long.
min_length = trim + substrate + penetration
Recommend the smallest common size ≥ min_length
18 ga brads (typical): 1, 1.25, 1.5, 2, 2.5 in
16 ga finish: 1, 1.25, 1.5, 1.75, 2, 2.5 in
That is why ½ in casing + ½ in drywall + ¾ in in the stud = 1.75 in recommends a 2 in 18-ga brad (1¾ is not on the 18-ga list) and can stay 1¾ in on 16-ga. If the sum is already a listed size, that size is the pick — no extra bump.
This is a US trim formula, not a Euro nail-gun chart and not a structural schedule. It will not tell you whether the stud is where you think it is, whether the trim will split, or whether a 2½ in nail will blow through a 3½ in stud from a thin stop. Hold the gun square, back up delicate profiles, and glue the joint if the fastener is only locating the piece.
| Trim | Substrate | Pen. | Min | 18 ga | 16 ga |
|---|---|---|---|---|---|
| 0.5 | 0.5 | 0.75 | 1.75 | 2 in | 1.75 in |
| 0.75 | 0 | 0.75 | 1.50 | 1.5 in | 1.5 in |
| 0.5 | 0.625 | 0.75 | 1.875 | 2 in | 2 in |
| 0.75 | 0.5 | 0.75 | 2.00 | 2 in | 2 in |
| 0.25 | 0.5 | 0.75 | 1.50 | 1.5 in | 1.5 in |
| 1.0 | 0.5 | 1.0 | 2.50 | 2.5 in | 2.5 in |
Rows check: min = trim + sub + pen, then the first size in the gauge list that is ≥ min. Default example: 0.5 + 0.5 + 0.75 = 1.75 → 2 in on 18 ga.
Add the trim, the drywall if any, and about ¾ in of stud bite, then go up to the next size your gauge actually stocks. Half-inch casing on half-inch drywall is a 2 in 18-ga brad in most US finish guns. Wood to wood with ¾ stock and ¾ in bite is a 1½ in nail.
18-ga brads leave a smaller hole and hide better in paint-grade casing; they also bend in oak and skip 1¾ in in a lot of collated boxes. 16-ga finish nails hold harder, stock 1¾ in, and leave a hole you will fill. This page only changes the size list. It does not pick the gauge for you.
Set substrate to 0 and use the jamb thickness as part of the trim, or type the jamb as the substrate. The formula does not care what the layers are named. You still want real bite in something solid. Drywall alone is not a stud.
A 2×4 is 3½ in thick. Trim ½ + drywall ½ + 2 in nail = 3 in of nail in a 3½ in stud if you hit it square — usually fine. A thin stop on a ¾ jamb is a different story; drop the penetration or the nail. This calculator does not know what is behind the wall.
No. Common US inch sizes only. Metric brads and 15-ga angled finish nails are out of scope. If your box is labelled 16 mm / 32 mm / 50 mm, convert and then pick, or use the millimetre stamp on the box against the min length in inches × 25.4.