Grommet Size Number to Hole Diameter Converter

Grommets and eyelets are metal rings inserted into holes in fabric, canvas, leather, or other sheet materials to reinforce the hole and prevent tearing. The size number system assigns a sequential number to each standard hole diameter, but the numbering tells you nothing on its own. Size 2 is 3/8 inch and size 4 is 1/2 inch, and there is no arithmetic connecting the two, so a table is the only way to know what you are buying.

Grommet vs eyelet terminology: A grommet consists of two parts: a barrel (the ring with a tube that passes through the hole) and a washer (a flat ring that clinches onto the back). An eyelet is typically a single-piece ring that rolls or flares over on the back side. In practice, the terms are often used interchangeably, though true grommets (two-piece) provide a stronger, more finished installation.

Standard grommet sizes and their hole diameters:

Material options:

• Brass: The most common grommet material. Naturally corrosion-resistant, easy to set, and available in plain (gold-tone) or nickel-plated finishes. Suitable for tarps, banners, shower curtains, and crafts.
• Stainless steel: More expensive but offers superior strength and corrosion resistance. Required for marine applications, outdoor signage in coastal areas, and anywhere exposed to salt water or harsh chemicals.
• Aluminum: Lightweight and corrosion-resistant but softer than brass. Used in lightweight applications and where weight is a concern.
• Plastic/nylon: Non-conductive and corrosion-proof. Used in electrical applications and where metal contact is undesirable.

Self-piercing (spur) grommets: Spur grommets have sharp teeth on the barrel that punch through the material during installation, eliminating the need to pre-cut a hole. They are faster to install but only work on softer materials like fabric, thin leather, and vinyl. For heavier materials like canvas or thick leather, always pre-punch the hole.

Installation tools:

• Hand setting tools: A die set and setter tool used with a hammer. Inexpensive but requires practice to get consistent results.
• Plier-type setters: Squeeze-handle tools for small grommets (sizes 00-2). Good for occasional use and crafts.
• Bench-mounted presses: Lever-operated presses that provide consistent, even pressure. The best choice for production work or large grommets.
• Hole punch: Cut the hole to the grommet’s own size, not larger. The size number is the finished inside diameter and it is also the punch size, so a #2 grommet wants a 3/8 inch punch. The barrel should push through snugly. A generously cut hole leaves the grommet floating in the fabric, and it will work loose under load no matter how well the washer is clinched.

A last word on which size to buy. Match the grommet to the load, not to the fabric. A tarp corner that will carry a bungee at highway speed wants a #2 or #3 even if the material is light, because the failure is almost never the grommet tearing, it is the grommet pulling through the cloth. Reinforce the corner with a doubled patch of the same material before you punch, and the same grommet will outlast the tarp.