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Aluminum Sheet vs Plate: Thickness, Temper and Use Cases
Aluminum Sheet vs Plate: Thickness, Temper and Use Cases
When you order aluminum, the difference between “sheet” and “plate” is not just a naming convention — it changes the manufacturing process, the tolerances you can hold, and the price. Sheet is thinner, plate is thicker, and the cutoff between them is not what most buyers assume. This guide explains where sheet ends and plate begins, how temper affects each, and which form to specify for common applications.
The Thickness Cutoff: Sheet vs Plate
The general industry rule is that aluminum under 0.200 inches (5.0 mm) is called sheet, and aluminum over 0.250 inches (6.3 mm) is called plate. The gap between 5 mm and 6.3 mm is a gray zone where suppliers may call it either. In practice, sheet is produced by cold rolling to very tight gauges, while plate is produced by hot rolling and then leveling. The cold rolling process for sheet gives a smooth surface and tight dimensional tolerance — typically ±0.05 mm on thickness. Plate, being hot-rolled, has a mill finish surface and looser tolerance — typically ±0.2 mm on thickness. See our 6061-T6 plate and 1060 sheet.
| Form | Thickness range | Surface | Thickness tolerance |
|---|---|---|---|
| Foil | < 0.2 mm | Bright/matte | ±0.01 mm |
| Sheet | 0.2 – 5.0 mm | Mill finish, smooth | ±0.05 mm |
| Gray zone | 5.0 – 6.3 mm | Either | ±0.1 mm |
| Plate | 6.3 – 200 mm | Hot-rolled mill finish | ±0.2 – 0.5 mm |
How Temper Changes the Game
Temper is the heat treatment condition of the aluminum, and it determines both strength and formability. For sheet, the common tempers are O (annealed, soft), H14/H16/H18 (strain-hardened), and H32/H34 (strain-hardened and stabilized). O-temper sheet bends and forms easily but is weak. H18 is the hardest sheet temper, strong but brittle. For plate, the dominant tempers are T6 (solution heat-treated and artificially aged) and T651 (stress-relieved by stretching). 6061-T6 plate is the workhorse of machined aluminum — it machines cleanly, holds tight tolerances, and has excellent strength. 5052-H32 sheet is the most common marine-grade aluminum, with good corrosion resistance and moderate strength.
Sheet Applications: When Thin Is Right
Sheet is used anywhere the part needs to be formed, bent, stamped or wound: gutters, roofing, siding, cookware, heat exchanger fins, curtain walls, automotive body panels, and electrical enclosures. For these applications, the sheet must be formable — you cannot stamp a T6 plate into a car body panel, because it will crack. Specify O or H32 temper for formed parts. For painted or powder-coated applications, H14 or H24 is standard — the surface is smooth enough to finish, and the strength is adequate for non-structural use. 1060-H14 sheet is the cheapest option for cosmetic or non-critical parts, while 3003-H14 is the standard for general sheet metal work.
Plate Applications: When Thickness Is Required
Plate is used when the part must be machined, welded, or carry load: machine bases, tooling plates, jigs, fixtures, truck beds, structural supports, marine components, and aerospace parts. For these applications, the plate needs to be thick enough to machine to final dimensions. 6061-T6 plate is the default for general machining — it cuts cleanly, anodizes well, and is available off-the-shelf. 7075-T6 plate is the high-strength option for aerospace and defense, with 503 MPa tensile strength but poor corrosion resistance. 5083-H116 plate is the marine-grade option, with excellent corrosion resistance and moderate strength. For tooling and fixtures, MIC-6 cast tooling plate is the flattest option, with minimal internal stress.
Common Buying Mistakes
The most common error is specifying “aluminum plate” when the part is actually 3 mm thick — that is sheet, and plate suppliers will charge a premium or refuse the order. The reverse mistake is ordering 3 mm sheet for a machined part, because sheet cannot be machined to tight tolerances (it warps under cutting forces). Another common mistake is ignoring the temper: ordering 6061-T6 sheet for a bent part — it will crack. Always specify the temper in the purchase order, because “6061 sheet” without a temper defaults to O or H14, which may not be what you want. For machined parts, specify T651 to get stress-relieved plate that will not warp after machining.
Weight and Cost Comparison
Aluminum density is 2.70 g/cm³. A 3 mm sheet weighs 8.1 kg/m². A 12 mm plate weighs 32.4 kg/m². The price per kilogram is roughly the same for sheet and plate of the same alloy, but the price per piece can differ dramatically because of processing. Thin sheet is sold by weight, but it is often priced per square meter for cosmetic applications. Thick plate is always sold by weight, and the price per kilogram increases with thickness because of slower rolling and more inspection. For large orders, always ask for a price per kilogram and a price per piece, and confirm whether cutting to size is included.
Surface Finish Options
Mill finish is the standard for both sheet and plate. For sheet, mill finish is smooth and ready for painting. For plate, mill finish is rough and should be machined or brushed before finishing. For architectural applications, sheet can be anodized, brushed, or polished. For plate, the surface is usually machined to a 125 or 63 RMS finish. If you need a specific surface roughness, specify it in the purchase order — mill finish is not a controlled surface, and suppliers will not guarantee a specific roughness.
Summary: Which to Specify
Use sheet for formed, bent, stamped or cosmetic parts under 5 mm. Use plate for machined, welded or structural parts over 6 mm. For sheet, specify the temper (O, H32, H14, H18) based on formability needs. For plate, specify T6 or T651 for machined parts. Always confirm the cutoff with your supplier, because the 5–6.3 mm gray zone is handled differently by different mills. And always ask for mill certificates to confirm the actual temper and mechanical properties.
