Standard Stock Sizes

Standard stock sizes are the thicknesses, widths, lengths and diameters that mills and stockholders actually produce: plate blanks of 2000 x 1000, 2500 x 1250 and 3000 x 1500mm, round bar from 10 to 250mm, structural tube from 21.3 to 406.4mm outside diameter in common mill stock, and acrylic sheet in steps from 1.5 to 25mm. A part designed inside these sizes can be cut from material the supplier already holds. A part that needs something else may wait on a mill.

Why stock sizes matter

Nesting, yield and lead time

The first question for any flat part is how it lays out on a standard blank. A 600 x 400mm bracket blank nests four across and three down on a 2500 x 1250mm sheet: 12 parts using 2.88 of the sheet’s 3.125 square metres, about 92 percent yield before kerf. At 3mm carbon steel, which weighs 7.85 grams per cubic centimetre, that sheet is about 73.6kg, so each blank carries roughly 5.6kg of paid-for material. Sizes that do not tile the sheet leave wider offcuts and a higher price per part, because you pay for the scrap.

Lead time follows the same logic. Stock sizes are on the shelf; non-stock sizes can force a mill order with its own minimum weight. The way to buy outside the standard steps is a special agreement, which the mill programs offer but at a cost in both price and waiting.

Stock versus custom

None of this means custom sizes are impossible. Quarto plate is rolled piece by piece, and the mill dimension program states plainly that other sizes can be delivered by special agreement. The practical rule is to treat stock steps as the default and step outside them only when the part genuinely needs it: a width that saves a weld, or a thickness that hits a calculated stiffness target.

Sheet and plate stock sizes

Standard widths and blank formats

Metric sheet starts from standard mill widths of 1000, 1250 and 1500mm for hot-rolled stainless, in thicknesses from 2.4 to 12.7mm. In the stockist’s rack, those widths become the familiar plate blanks: 2000 x 1000, 2500 x 1250 and 3000 x 1500mm, at thickness steps of 3, 4, 5, 6, 8, 10 and 12.5mm for mild steel. Quarto plate goes bigger, in widths from 1500 to 3200mm (the mill program reaches about 3260mm) and lengths up to about 13.5 metres. Inch-market stock, plastics in particular, ships as 48 x 96in sheets, which is 1220 x 2440mm.

Below 3mm, carbon steel sheet is sold by gauge number, and the scale differs by metal. The sheet metal gauge chart carries those conversions; for planning, the common fabrication band is 18 to 14 gauge, about 1.2 to 1.9mm.

Nominal versus actual thickness

A stock size is nominal, which means it is a name, not a measurement. EN 10029:2010 governs hot-rolled plate from 3mm up, and when the order states no tolerance class, class A applies: -0.3/+0.7mm on 3 to 5mm plate, -0.5/+0.9mm in the 8 to 15mm band, and -1.2/+2.4mm at 150 to 250mm. A 10mm plate can therefore arrive anywhere between 9.5 and 10.9mm and still be compliant. Classes B, C and D tighten specific sides of that band: B holds a fixed -0.3mm floor, C removes the minus tolerance, and D splits the tolerance symmetrically. Call the class when a fit or a weight calculation depends on the real thickness.

Round bar stock sizes

Metric steps and the inch trap

Hot-rolled round bar to EN 10060:2003 is made in nominal diameters from 10 to 250mm. The steps a stockist actually carries are 10, 12, 16, 20, 25, 30, 32, 40, 50, 63, 80 and 100mm, and the table lists those with exact inch equivalents. The tolerance on diameter is wide by machining standards: about ±0.4mm at 10 to 15mm, ±0.5mm to 25mm, and ±1.0mm by 80mm. Schedules differ by one step at the 16mm boundary, where one mill table reads ±0.4mm and the association reading used here is ±0.5mm, so confirm the band with the supplier when the margin matters. Bright (cold-drawn) bar to EN 10278:1999 uses ISO 286 h-classes instead, for example 0.110mm of total spread at h11 for 10 to 18mm, with ground bar reaching h7. For machined parts, order bright or ground bar and leave hot-rolled for welded frames.

The inch trap catches someone every week: one inch is exactly 25.4mm, so 1in bar is not the same stock as 25mm bar, which measures 0.984in. Both sizes sit in the same rack, so confirm which series a drawing means before it goes to the saw.

Tube and pipe stock sizes

Two series that almost match

Structural hollow sections to EN 10219-2:2006 run from 21.3mm up to 406.4mm outside diameter in common mill stock (the standard’s series continues larger), with walls from 2.0 to 12.5mm, and the table lists the common circular steps from 21.3 to 219.1mm. Steel pipe to ASME B36.10M-2018 is a different system: nominal pipe size (NPS) for the name and a schedule number for the wall. The outside diameters almost match the structural series, which is exactly why they get confused. NPS 3/4 pipe measures 26.7mm outside diameter while the structural step is 26.9mm, and a 2in schedule 40 pipe is 60.3mm outside diameter with a 3.91mm wall. Order structural tube by outside diameter and wall, and pipe by NPS and schedule, and the two never cross.

Plastic stock sizes

Sheet steps and rod diameters

Plastics use their own metric steps, not metal gauges. Extruded acrylic comes in 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20 and 25mm in a 3050 x 2050mm format; cast acrylic starts at 2mm in 3050 x 2030mm sheets and extends to blocks 160mm thick. Black ABS sheet runs 1 to 10mm in 2000 x 1000mm blanks. HDPE stock sheet spans about 3 to 38mm in 1220 x 2440mm sheets. Rod is stocked in 2000mm lengths, extruded acrylic at 3 to 50mm diameter and HDPE at 10 to 120mm, with larger diameters to order. Because these steps do not match steel gauges, a drawing that mixes a plastic panel with a steel panel needs two thickness callouts, each in mm.

Limitations

Stock programs vary by region and supplier, and they change: the mill dimension program behind the plate table states that available sizes may differ from its published tables. The values here are the common verified steps, not a promise of what your supplier holds today. Tolerances sit at the standard level, so confirm the class as well as the size: EN 10029:2010 classes for plate, EN 10060:2003 bands for hot-rolled bar, ISO 286 h-classes for bright bar. For load-critical or fit-critical work, confirm size, format and tolerance with the supplier before the order is released.