How Thick Should a Metal Planter Be? A Specifier's Guide to Wall Thickness and Gauge
Last updated: October 14, 2026
TL;DR
Metal planter wall thickness should be specified in inches or millimetres, because the same gauge number means different thicknesses in steel and aluminum. Urban Pot's standard aluminum planters use a 1/8 in (3.2 mm) 5052-H32 wall on all 19 catalog SKUs, with internal partitions on spans over 60 in. Custom aluminum is 1/8 in typical, with 3/16 in and 1/4 in available. Corten steel planters run from 3 mm (about 1/8 in) for small units to 6 mm (1/4 in) or more for large planters and integrated seating, with 5 to 6 mm recommended for vandalism-prone public sites.
Metal planter thickness is the measured thickness of the sheet that forms a planter's walls and base, stated in inches or millimetres. Gauge is an older numbering system for the same measurement, and it does not mean the same thing across metals. In mild steel, 11 gauge is 0.1196 in, but in aluminum the same 11 gauge is only 0.0907 in.
That is why Urban Pot publishes wall thickness in inches and millimetres. The standard aluminum planters, made in Canada and delivered to projects across Canada and the United States, use a 1/8 in (3.2 mm) 5052-H32 wall on every catalog size.
This guide covers how gauge relates to thickness, what the aluminum and steel lines actually specify, why larger planters get internal partitions instead of heavier walls, how the coating tier affects service life, and how to write thickness into a submittal using the documents in our BIM and specification library.
Gauge vs Wall Thickness: Why Gauge Numbers Mislead on Metal Planters
A gauge number only describes a thickness once you know the metal. Steel, galvanized steel, stainless steel and aluminum each follow their own gauge table, so the same number can differ by more than 0.02 in between metals. In a planter specification, a decimal or fractional thickness with a millimetre value is the only unambiguous figure.
The gap matters most when a drawing says "11 gauge" without naming the material. On the Metal Supermarkets sheet metal gauge chart:
11 gauge mild steel is 0.1196 in (3.04 mm)
11 gauge galvanized steel is 0.1233 in (3.13 mm)
11 gauge stainless steel is 0.1250 in (3.18 mm)
11 gauge aluminum is 0.0907 in (2.31 mm)
That is why the technical documents for the standard planter range state thickness, alloy and temper rather than gauge. A line such as "0.125 in (3.2 mm) 5052-H32 aluminum" leaves nothing for a fabricator or reviewer to interpret.
Aluminum Planter Thickness: The 1/8 in 5052-H32 Baseline
The standard aluminum line uses 1/8 in (3.2 mm) 5052-H32 aluminum sheet to ASTM B209, the standard specification for aluminum and aluminum-alloy sheet and plate. The same nominal wall applies to all 19 SKUs in the standard catalog, across cube, rectangle and cylinder shapes.
The rest of the standard build is fixed as well:
Top lip: 1 to 2 in (25 to 51 mm) formed return, with the vertical leg no longer than the horizontal lip
Finish: exterior-grade, UV-resistant powder coat applied inside and out at 2.0 to 4.0 mil (50 to 100 µm) dry film thickness
Options: drainage holes and toe kick
Coating tiers: AAMA 2604 standard, AAMA 2605 premium on request, AAMA 2603 for interior use only
For custom aluminum planters, 1/8 in remains the typical wall, and 3/16 in (about 4.7 mm) or 1/4 in heavy-gauge walls are available as an upgrade for vandalism-prone or high-impact streetscapes. You can model a custom rectangular or round planter at the standard wall in our 3D planter configurator, which exports a PDF spec sheet with dimensions and volume.
How Thick Should a Steel Planter Be?
Steel planter thickness depends on the planter's size and load. In Corten steel planters, wall thickness typically starts at 3 mm (about 1/8 in) for small units. For larger structural pieces, retaining walls or integrated seating, Corten steel planter thickness moves to 6 mm (1/4 in) or more.
Where vandalism is a concern on public planters, we recommend 5 to 6 mm (about 1/4 in) Corten for dent resistance and rigidity under heavy public use, as the streetscape planter specification guide also notes. Corten wall thickness usually falls into three bands:
3 mm (about 1/8 in): small planters
5 to 6 mm (about 1/4 in): vandalism-prone public sites
6 mm (1/4 in) or more: larger structural pieces, retaining walls and integrated seating
Final steel thickness is still set per project at the quote and shop drawing stage. It depends on planter dimensions, soil pressure, anchoring, exposure and fabrication method, the same variables covered in the rooftop planter specification guide. Grade and finish can be specified up front for each steel line:
Weathering steel: Corten to ASTM A588 or A606, supplied raw or with an accelerated patina.
Stainless steel: Type 304 or 316 to ASTM A240, brushed or powder coated, typically chosen for coastal and high-touch locations. The stainless steel planters page covers the standard range.
Galvanized steel: hot-dip galvanized, powder coated or weathered, suited to high-traffic, value-driven projects.
Because each of these steels uses a different gauge table, ask for the thickness in inches or millimetres on the shop drawing rather than accepting a gauge number alone.
Planter line | Material and standard | Published wall thickness | Where it is confirmed | Typical use |
Standard aluminum | 5052-H32, ASTM B209 | 1/8 in (3.2 mm), all 19 SKUs | UP-TDS-SAL-001 and 2D CAD details | Commercial, hospitality, rooftop, streetscape |
Custom aluminum | 5052-H32, ASTM B209 | 1/8 in typical; 3/16 in and 1/4 in available | Project shop drawings | Rooftop, repositioning, custom geometry |
Weathering steel | Corten, ASTM A588 / A606 | 3 mm (1/8 in) for small units; 6 mm (1/4 in) or more for large or loaded units; 5 to 6 mm for vandalism-prone public sites | Final per project shop drawings | Streetscape, naturalized patina, statement pieces |
Stainless and galvanized steel | 304/316 ASTM A240; hot-dip galvanized | Set per project | Quote and shop drawings | Coastal and high-touch; high-traffic |
Note: Aluminum values from Urban Pot technical data sheets UP-TDS-SAL-001 and UP-TDS-CAL-001, Rev C (July 2026); Corten values reflect Urban Pot fabrication guidance as of October 2026. Data sheets are not for construction; confirm current values with Urban Pot before issuing a specification.
Planter Size, Long Spans and Internal Partitions
Larger standard planters do not get thicker walls. Every SKU keeps the 1/8 in (3.2 mm) wall, and any planter with a linear span over 60 in (1524 mm) gets internal structural partitions as standard to control wall deflection. In the standard catalog, that rule applies to the 72 in and 96 in rectangles.
Keeping one wall thickness also keeps weights predictable. Empty weights in the standard catalog range from 17 lb (8 kg) for the 16 in cube to 207 lb (94 kg) for the 96 x 48 x 42 in rectangle. Listed weights and volumes are theoretical and can vary by up to 10% in the field. A separate article on lightweight planters for rooftop load restrictions explains how saturated soil and drainage layers add up, and the planter calculation tools help estimate soil volume.
Custom planters follow a different limit. Single-piece fabrication is typically coordinated up to 144 in (3,658 mm) in length, and longer runs are built as segmented or field-joined assemblies per approved shop drawings.
The same approach holds on large custom runs. On the Crown Condominiums project in Kingston, Ontario, some of the eight marine-grade aluminum planters stretch over 7 m in length, yet the walls stay at 1/8 in. The runs were built in modular sections with concealed welds rather than heavier sheets, and the planters sit at both the entrance level and the sixth-floor rooftop terrace.
Coating Tier, Warranty and Wall Thickness
Wall thickness does not change Urban Pot's published warranty or durability terms. Our metal planters carry a 10-year structural warranty covering the substrate, welds and base. For standard aluminum planters, that coverage includes corrosion perforation. The paint finish carries a 3-year warranty, and the coating tier decides how well that finish holds up on site.
The difference between coating tiers shows up in testing. Under ASTM B117 salt-spray testing, AAMA 2604 requires 3,000 hours and AAMA 2605 requires 4,000 hours, with 5 and 10 years of South Florida exposure respectively. Both tiers are published as AAMA voluntary specifications through FGIA, and the technical data sheets list AAMA 2605 as the typical choice for coastal and severe exposure.
Salt and fertilizer residue is corrosive, so it should be rinsed off and water should not pool at the base. The operation and maintenance guide covers cleaning and seasonal care.
When a Project Moves to Custom Wall Thickness
A project moves to the custom line when the standard catalog no longer fits the site. The custom technical data sheet lists the triggers: dimensions outside the 19 standard SKUs, runs longer than single-piece fabrication allows, integrated benches, lighting or anchoring, rooftop, wind-exposed or security-critical locations, non-standard colours, and project-specific drainage or thermal lining.
In those cases, wall thickness is decided together with the rest of the assembly, not on its own. Anchored and rooftop installations get structural calculations arranged through the project's Engineer of Record and signed and sealed. Anchor hardware and pattern depend on the substrate, exposure, planter size and the approved shop drawings.
The La Cité university campus in Ottawa shows what a load-driven change looks like. Its five 68 in diameter marine-grade aluminum planters have a 1/4 in aluminum base with added reinforcement to carry a 25 cm (about 10 in) concrete pour placed on site. The planters conceal certified safety bollards, which provide the vehicle protection, while the planters and their Ipe wood benches turn that perimeter into campus seating.
One clarification for security-sensitive sites: a heavier wall adds mass and stiffness, but it does not make a planter a crash-rated vehicle barrier. Planters like these work as perimeter definition and visual deterrents, not as certified impact hardware. The custom planters for architects and designers page outlines how these requirements are coordinated from design through installation.
Specifying and Verifying Planter Thickness in a Submittal
Wall thickness is easiest to protect when it is written into the specification and checked at submittal. Our CSI MasterFormat 32 94 33 guide specification states a nominal wall thickness of 3.2 mm (1/8 in) and requires any "or approved equal" substitution to show equivalent material, thickness, configuration, finish and performance. Overall exterior length, width and height are held to a ±1/8 in (about 3 mm) manufacturing tolerance on standard and custom planters.
A clear planter specification should include:
Wall thickness in inches and millimetres, never gauge alone
Alloy and temper, or steel grade, with the governing ASTM standard
The internal partition requirement for spans over 60 in (1524 mm)
Coating tier (AAMA 2604 or 2605) and dry film thickness
Shop drawing approval before fabrication for any custom unit
Custom work is welded to AWS D1.2 and CSA W59.2 for aluminum. Wherever aluminum, stainless steel or Corten meets a dissimilar metal, separation layers such as isolation washers, rubber gaskets and compatible fasteners prevent galvanic corrosion. Concrete is a separate case because it is not a metal: where aluminum sits on fresh or wet concrete, a barrier or protective coating keeps the concrete's alkalinity from attacking the aluminum. If the planter also needs a liner or thermal lining, the guide to planter liners and waterproofing covers how to coordinate it with the shell.
Frequently Asked Question
How thick should a Corten steel planter be?
Corten steel planters typically range from 3 mm (about 1/8 in) for small units to 6 mm (1/4 in) or more for large planters, retaining walls and integrated seating. For vandalism-prone public sites, we recommend 5 to 6 mm for dent resistance and rigidity. Final thickness is confirmed on the project shop drawings.
Why specify planter wall thickness in millimetres instead of gauge?
Millimetres are unambiguous, while the same gauge number means different thicknesses in different metals. 11 gauge mild steel is 0.1196 in (3.04 mm), but 11 gauge aluminum is only 0.0907 in (2.31 mm). Stating inches and millimetres with the alloy or steel grade leaves nothing for a fabricator or reviewer to interpret.
When should a project upgrade to a thicker planter wall?
Upgrade when the site is vandalism-prone, high-impact or structurally loaded. For aluminum, that means 3/16 in (about 4.7 mm) or 1/4 in custom walls instead of the standard 1/8 in. For Corten, 5 to 6 mm suits public sites, and 6 mm or more suits retaining walls and integrated seating.
What should a metal planter specification include?
A metal planter specification should state wall thickness in inches and millimetres, the alloy or steel grade with its ASTM standard, internal partitions for spans over 60 in, the coating tier and dry film thickness, and shop drawing approval for custom units. Overall dimensions are held to ±1/8 in (about 3 mm).
Does a thicker wall make a planter a vehicle barrier?
No. A heavier wall adds mass and stiffness, but it does not make a planter a crash-rated vehicle barrier. Our planters work as perimeter definition and visual deterrents. Where vehicle protection is required, certified bollards can be concealed inside custom planters, as on the La Cité campus project in Ottawa.
Getting Metal Planter Thickness Right the First Time
A durable metal planter is not the result of a heavier gauge number. It comes down to a stated thickness in inches or millimetres, the right alloy or steel grade, and a coating tier matched to the site.
Specifying those three items early prevents substitution disputes at submittal and separates a documented planter from a catalog guess. Urban Pot works with architects and landscape architects to confirm wall thickness, partitions and finish before shop drawings are approved, whether the project calls for standard aluminum planters or a weathering steel run built to project dimensions.
