PreConstruct AIA partition schedule says 92 mm steel studs @ 406 o.c., 0.45 mm, a supplier's price sheet says 3-5/8" 25 ga, and the submittal says 362S125-18. They can all be the same stud. This guide lines up gauges, mils, millimetres and sizes so you can read any of them, then turns a wall into a stud and track order.
Gauge, mils and millimetres
Gauge is the old trade name. Mils are the minimum base-steel thickness in thousandths of an inch, and that's what the standards and submittals use. Canadian drawings often give the thickness in millimetres.
| Gauge (as sold) | Mils (minimum) | Minimum thickness | Typical use on a schedule |
|---|---|---|---|
| 25 | 18 | 0.45 mm (0.0177 in) | Non-structural interior partitions |
| 20 drywall | 30 | 0.75 mm (0.0296 in) | Non-structural, stiffer: taller walls, tile, door jambs |
| 20 structural | 33 | 0.84 mm (0.0329 in) | Structural (ASTM C955) and some non-structural uses |
| 18 | 43 | 1.09 mm (0.0428 in) | Structural framing, heavy partitions |
| 16 | 54 | 1.37 mm (0.0538 in) | Structural framing, curtain-wall backup |
| 14 | 68 | 1.72 mm (0.0677 in) | Heavy structural framing |
The typical-use column is what you'll usually see, not a rule. Which stud a wall needs comes from the partition schedule and the stud maker's limiting-height tables, and the engineer's drawings for anything structural.
The two 20 gauges
“20 gauge” means two different products. The drywall 20 gauge is 30 mil, made to the non-structural standard (ASTM C645). The structural 20 gauge is 33 mil, made to the structural standard (ASTM C955). They look almost the same on the truck. When a schedule or quote just says “20 ga”, find out which one it means, because the price and what the wall can do both change.
EQ studs
EQ (“equivalent”) studs use thinner, higher-strength steel, stiffened with dimples, knurling or ribs, and are sold as performing like the gauge they're named after: a “20EQ” is meant to do the job of a 20 gauge drywall stud. They're non-structural only, and their actual thickness varies by maker. Before pricing an EQ stud against a schedule that names a gauge or a thickness, check the maker's data sheet, and check the fire-rated design if the wall is rated, because some listings name the stud they were tested with.
Reading a stud designation
Makers in Canada and the US use the same four-part code: web depth, type, flange width, thickness. The first two numbers are hundredths of an inch, and the last is mils.
362S125-18: a 3⅝ in stud (S) with 1¼ in flanges, 18 mil. That's the everyday 25 gauge partition stud.362T125-18: the matching track (T).600S162-33: a 6 in stud with 1⅝ in flanges, 33 mil.
Stud sizes in inches and millimetres
| Web depth | Millimetres | Where you see it |
|---|---|---|
| 1⅝ in | 41 mm | Furring walls, chases, shaft liners |
| 2½ in | 64 mm | Thin partitions |
| 3⅝ in | 92 mm | The common interior partition |
| 4 in | 102 mm | The common interior partition |
| 6 in | 152 mm | Tall walls, plumbing walls, exterior backup |
Studs are cut to order or stocked in lengths from 8 to 24 ft. Track comes in 10 ft (3.05 m) pieces. Drawings often round the depths to 41, 64, 92, 102 and 152 mm.
How many studs and how much track
| Spacing | Studs per metre of wall | Studs per foot |
|---|---|---|
| 300 mm (12 in) | 3.28 | 1.00 |
| 400 or 406 mm (16 in) | 2.46 | 0.75 |
| 600 or 610 mm (24 in) | 1.64 | 0.50 |
Add one stud to close each run, then the extras at openings, corners and tees (how many is in the details), then waste. Track is two lengths of wall, top and bottom. Where a wall runs to the deck, the head is usually a deflection track (a deep-leg or slotted track, or a double track), which is a different product and price from the bottom track. The detail shows which.
A worked order
A corridor partition 30 m long, studs at 406 mm, 4 doors taking 3 extra studs each, and 3 tees taking 2 each. Stud waste 5%, track waste 10%.
- Layout:
30,000 ÷ 406 = 73.9 → 74, + 1 = 75 studs - Extras:
4 × 3 + 3 × 2 = 18 - With waste:
(75 + 18) × 1.05 = 97.7 → 98 studs, at the wall's height - Track:
30 m × 2 = 60 m, with waste66.0 m ÷ 3.048 m = 22 piecesof 10 ft, before separating the deflection track at the head
Keep studs of different heights and gauges on separate lines. A job with 3 m and 4.2 m walls, or 25 and 20 gauge, is really two or four orders.
Doing it on the drawings
In PreConstruct AI a wall type names its stud and track, the spacing and the extras at openings and corners, the way your partition schedule does. Draw the walls and the studs come out counted at the wall's height, with the track, board, batts and finishing beside them and the arithmetic on each line. The gauge, depth and spacing are the ones on your schedule. It counts and measures, and never picks a stud.