Steel plate in Canada is stocked mainly in fractional-inch thicknesses, from 3/16 in (4.8 mm) and 1/4 in (6.4 mm) up through 1 in (25.4 mm) and beyond, with each thickness weighing 7.85 kg per square metre for every millimetre. So 1/4 in plate weighs about 49.8 kg/m² (10.2 lb/ft²) and 1/2 in plate about 99.7 kg/m². Metric drawings that call for 6, 10 or 12 mm plate are usually filled with the nearest imperial thickness. The chart below lists the standard thicknesses with decimal inches, millimetres and weights, followed by sheet gauges and metric equivalents.
Steel plate thickness chart
Weights are calculated from a steel density of 7,850 kg/m³ and rounded. Actual plate varies slightly within mill rolling tolerances.
| Thickness (in) | Decimal (in) | Thickness (mm) | Weight (kg/m²) | Weight (lb/ft²) |
|---|---|---|---|---|
| 3/16 | 0.1875 | 4.8 | 37.4 | 7.7 |
| 1/4 | 0.2500 | 6.4 | 49.8 | 10.2 |
| 5/16 | 0.3125 | 7.9 | 62.3 | 12.8 |
| 3/8 | 0.3750 | 9.5 | 74.8 | 15.3 |
| 7/16 | 0.4375 | 11.1 | 87.2 | 17.9 |
| 1/2 | 0.5000 | 12.7 | 99.7 | 20.4 |
| 5/8 | 0.6250 | 15.9 | 124.6 | 25.5 |
| 3/4 | 0.7500 | 19.1 | 149.5 | 30.6 |
| 7/8 | 0.8750 | 22.2 | 174.5 | 35.7 |
| 1 | 1.0000 | 25.4 | 199.4 | 40.8 |
| 1-1/4 | 1.2500 | 31.8 | 249.2 | 51.0 |
| 1-1/2 | 1.5000 | 38.1 | 299.1 | 61.3 |
| 1-3/4 | 1.7500 | 44.5 | 348.9 | 71.5 |
| 2 | 2.0000 | 50.8 | 398.8 | 81.7 |
| 2-1/2 | 2.5000 | 63.5 | 498.5 | 102.1 |
| 3 | 3.0000 | 76.2 | 598.2 | 122.5 |
| 4 | 4.0000 | 101.6 | 797.6 | 163.4 |
Not every thickness is stocked everywhere. Published stock lists from plate distributors and service centres commonly run in 1/16 in steps from 3/16 to 3/8 in and 1/8 in steps to 1 in, then in larger steps, with plate several inches thick available for heavy industrial work. Ask your supplier which thicknesses are on hand, especially for the odd sizes like 7/16 and 1-3/4 in.
Rule of thumb for weight: every millimetre of thickness adds 7.85 kg per square metre, and every inch adds about 40.8 lb per square foot. For the weight of a specific part, see our steel plate weight calculator.
Quarter inch steel plate
1/4 in plate is the thickness people ask about most, because it's the lightest common structural plate and a typical choice for brackets, clips, light covers and many small parts.
- Thickness: 0.25 in, 6.35 mm (written 6.4 mm)
- Weight: about 49.8 kg/m², 10.2 lb/ft²
- A 4 x 8 ft sheet: about 148 kg (327 lb)
- A 300 x 300 mm plate: about 4.5 kg
Whether 1/4 in is thick enough for a given part is a design question. Base plates, cap plates and connection plates carry concentrated forces, and their thickness comes from the column load, bolt layout and bending in the plate, not from a rule of thumb. Our base plate size and thickness chart explains how that's worked out.
Sheet steel gauges
Below about 1/4 in, flat steel is usually sold as sheet and ordered by gauge. Gauge numbers run backwards (a higher number is thinner), and they aren't the same for every material. The values below are the manufacturers' standard gauge for uncoated carbon steel sheet. Galvanized sheet, stainless steel and aluminium each use slightly different thicknesses for the same gauge number.
| Gauge | Thickness (in) | Thickness (mm) | Weight (kg/m²) |
|---|---|---|---|
| 7 | 0.1793 | 4.55 | 35.8 |
| 8 | 0.1644 | 4.18 | 32.8 |
| 10 | 0.1345 | 3.42 | 26.8 |
| 11 | 0.1196 | 3.04 | 23.8 |
| 12 | 0.1046 | 2.66 | 20.9 |
| 14 | 0.0747 | 1.90 | 14.9 |
| 16 | 0.0598 | 1.52 | 11.9 |
Because gauge depends on the material and the gauge system, it's safer to order sheet by decimal thickness or millimetres. If a drawing says "10 ga", confirm whether it means uncoated or galvanized sheet.
Metric plate thicknesses and their imperial substitutes
Drawings from engineers often show metric plate thicknesses. Since most plate in Canadian stock is imperial, here is what usually gets supplied:
| Drawing calls for | Nearest imperial | Actual (mm) | Difference |
|---|---|---|---|
| 6 mm | 1/4 in | 6.4 | 0.4 mm thicker |
| 8 mm | 5/16 in | 7.9 | 0.1 mm thinner |
| 10 mm | 3/8 in | 9.5 | 0.5 mm thinner |
| 12 mm | 1/2 in | 12.7 | 0.7 mm thicker |
| 16 mm | 5/8 in | 15.9 | 0.1 mm thinner |
| 20 mm | 3/4 in | 19.1 | about 1 mm thinner |
| 25 mm | 1 in | 25.4 | 0.4 mm thicker |
Where the imperial plate is thinner than specified (10 mm to 3/8 in, 20 mm to 3/4 in), the substitution reduces strength slightly. Where it's thicker, it may affect fit-up, weld sizes or clearances. Either way, for structural parts it's a design change: the designer or engineer should accept it before fabrication. Some designers specify the imperial-equivalent thickness (PL 9.5, PL 12.7) to avoid the question. Thickness is also separate from grade; see steel plate grades in Canada.
How thickness is measured and specified
A few practical points when you read or write a plate thickness:
- "PL" notation. Drawings typically show plate as PL thickness x width x length, for example PL 12.7 x 300 x 300 or PL 1/2 x 12 x 12. Some show thickness last; check the drawing's convention.
- Nominal vs actual. Plate is rolled to a nominal thickness with permitted variations set out in the product standards (for example ASTM A6 or CSA G40.20). The plate you receive may measure slightly over or under nominal, which is normal.
- Checker plate thickness normally refers to the plate itself, not the raised pattern, but confirm how each supplier states it. More in steel checker plate.
- Units. Write thickness in the same units throughout a drawing or order. Mixing 12 mm and 1/2 in on one list is how the wrong plate gets cut.
Getting plate cut to the right thickness
For sizes and sheet weights, see our steel plate sizes guide. For structural parts, most plate is ordered cut to size from drawings rather than as full sheets.
We cut and drill base plates, cap plates and connection plates to your details, and weld them to posts and beams when the drawings call for it. Send the thickness, grade and a drawing or DXF for each part.
Request a quote for your plate parts, or browse our steel products, including plates, posts and beams.
Frequently asked questions
What are the standard thicknesses of steel plate?
In Canada plate is mostly stocked in fractional-inch thicknesses: 3/16, 1/4, 5/16, 3/8, 1/2, 5/8, 3/4, 7/8 and 1 in, then 1-1/4, 1-1/2, 2 in and up. In millimetres those are 4.8, 6.4, 7.9, 9.5, 12.7, 15.9, 19.1, 22.2 and 25.4 mm.
How thick is quarter inch steel plate in mm?
1/4 in is 6.35 mm, usually written 6.4 mm on drawings. It weighs about 49.8 kg per square metre (10.2 lb per square foot), so a 4 x 8 ft sheet weighs about 148 kg.
What thickness is steel plate vs sheet?
In the trade, flat steel thinner than about 1/4 in (6.4 mm) is usually called sheet and ordered by gauge, and 1/4 in and thicker is called plate. Some suppliers list 3/16 in material with their plate.
Can I get 10 mm or 12 mm steel plate in Canada?
Metric plate can be sourced, but most Canadian stock is imperial, so 10 mm is often supplied as 3/8 in (9.5 mm) and 12 mm as 1/2 in (12.7 mm). For structural parts, the designer should accept the substitution.
