Aluminium Plate Thickness & Sheet Gauge Chart

Where sheet ends and plate begins

The boundary between aluminium sheet and plate is set by the standards. Under the Aluminum Association and ASTM B209 definitions, sheet is 0.006 – 0.249 in (about 0.15 – 6.3 mm) thick and plate is 0.250 in (6.35 mm) and thicker; anything thinner than 0.006 in is foil. European terminology draws the line at 6 mm, so a 6 mm product is sheet and 8 mm is plate.

The distinction matters because sheet and plate are listed in different tables of the standards, with different tolerances, tempers and minimum properties. Thick plate in heat-treatable alloys is supplied in stress-relieved tempers such as T651 or T7451, while sheet is usually T6 or T4. In practice buyers often say "plate" for anything thicker than about 3 mm; when ordering, give the thickness and the standard so there is no ambiguity.

2 – 6 mm aluminium sheet and thin plate

This is the busiest range of the market: 2, 3, 5 and 6 mm sheet are bought for cladding, signage, enclosures, vehicle panels, boat building and general fabrication. Typical alloys are 1050, 1100, 3003, 5052, 5754 and 6061, in tempers such as O, H14, H24, H32 and T6. The range is also where most processed sheet sits: chequer and tread plate, perforated sheet and anodised or colour-coated sheet.

• 2 – 3 mm: facade and ceiling panels, signs, light covers, enclosures and appliance parts
• 4 – 5 mm: partitions, truck bodies, industrial housings, chequer plate floors and steps
• 6 mm: boat hulls and decks in 5083 or 5754, vehicle floors, base plates and small tooling

6 – 25 mm medium plate

Medium plate carries structural loads. Common thicknesses are 8, 10, 12, 16, 20 and 25 mm. The usual alloys are 6061 and 6082 in T6 or T651 for machined and structural parts, and 5083 or 5754 in H111, H116 or H321 for marine and pressure work, with 7075-T651 where high strength is needed.

Typical uses include building and bridge connection plates, platforms and walkways, truck and trailer chassis members, marine decks and bulkheads, machine base plates and brackets. Face milling, cut-to-size blanks and PVC film protection are common processing options at this thickness.

25 – 200 mm thick plate

Thick plate is bought mainly for machining: mould bases, jigs and fixtures, machine frames, vacuum chambers and aerospace ground tooling. Popular thicknesses are 30, 40, 50, 60, 80, 100 and 150 mm. Alloys are 6061-T651, 6082-T651, 7075-T651, 2024-T351 and 7050-T7451, plus cast tooling plate for applications that need flatness more than strength.

Two things change as plate gets thicker. First, the guaranteed minimum strength of heat-treatable alloys falls slightly, because the centre of a thick plate cools more slowly during quenching; the standards list lower minimums for thicker bands. Second, residual stress becomes the main machining risk. Stretched tempers (T651, T7351, T7451) relieve most of it, so parts stay flat when large volumes of metal are removed. For aerospace and critical parts, specify ultrasonic inspection of thick plate.

Plate and blocks over 200 mm

Above about 200 mm, rolled plate becomes a specialist product and is normally made to order for a project. Depending on alloy and size, very thick sections may be supplied as rolled plate, as forged blocks or as cast and stress-relieved blocks. Typical alloys are 6061, 7075, 7050 and 2219. Ultrasonic inspection to a recognised class is normal, and properties are confirmed by testing the actual product.

Typical uses are aerospace spars and frames machined from solid, large press and machine bases, defence structures and parts for energy and process equipment. Because each of these is made to order, give the finished part envelope as well as the plate size, so the most efficient product form can be proposed. See our aluminium block range and forged plate for these products.

Common inch thicknesses converted to millimetres

North American mills and stockists list plate in fractional inches. The table converts the common fractions and gives the weight per square foot and per square metre.

Weights use a density of 2.70 g/cm³ (0.0975 lb/in³), which suits 6061 and most 1xxx and 3xxx alloys. 5083 is about 1.5 % lighter, 7075 about 4 % heavier and 2024 about 3 % heavier.

Aluminium sheet gauge chart

Gauge numbers are still common for thin sheet in the United States. Aluminium uses the Brown & Sharpe system (also called American Wire Gauge), which is not the same as the Manufacturers' Standard Gauge used for steel. A 16 gauge aluminium sheet is about 1.29 mm, while 16 gauge steel is about 1.52 mm. Always confirm the decimal thickness when ordering by gauge.

Gauge is rarely used above about 6 gauge (4.1 mm), and never for plate. Outside North America, sheet is normally specified in millimetres, so a metric order for "1.2 mm" is clearer than "18 gauge" (1.02 mm). For quoting, Metline accepts thickness in mm, inch or gauge and confirms the decimal value on the quotation.

Alloys and tempers by thickness

How to choose the right thickness

1. Design for stiffness, not just strengthAluminium has about one third of the elastic modulus of steel. Bending stiffness of a plate rises with the cube of thickness, so going from 3 mm to 4 mm increases stiffness by about 2.4 times.
2. Add machining allowanceFor machined parts, order plate a few millimetres thicker than the finished part so both faces can be cleaned up, or order precision-milled plate.
3. Use a standard thicknessStandard thicknesses are produced in larger volumes and are quicker and cheaper to supply than odd sizes.
4. Check the standard's thickness bandMinimum properties and tolerances change with thickness. Confirm the values for your band in ASTM B209 or EN 485-2.
5. Mind the gauge systemWhen converting a steel drawing, do not assume the same gauge number means the same thickness in aluminium.

Weight of standard sheet and plate sizes

For handling, freight and quoting it helps to know the weight of a whole sheet. The figures below use 2.70 g/cm³; multiply by 0.985 for 5083 and by 1.04 for 7075.

A 2000 × 4000 × 50 mm plate weighs more than a tonne, so thick plate is usually cut to smaller blanks before shipping unless the full size is needed. For any other size, use the plate weight calculator.

Processing options by thickness

Flatness is controlled by the standard tolerance tables for mill plate, but stretched T651-type tempers and precision-milled plate give much better results after machining. If flatness is critical, state the required value on the order rather than relying on the default tolerance.

Related plate grades and tools

Aluminium plate thickness and gauge: frequently asked questions