Glass Thickness Explained: 3 mm to 12 mm, and Why Thick Glass Looks Green

Glass thickness is one of the first lines on any order, and one of the easiest to get wrong. Too thin and the glass can deflect, break under wind load, or fail a code review. Too thick and you pay for weight and cost the frame never needed. Here is how the decision usually gets made.

The common thicknesses

Flat glass for buildings is typically made in 3, 4, 5, 6, 8, 10, and 12 mm. Residential windows and IGUs mostly use 3 to 5 mm panes. Patio doors, larger windows, and light commercial work move into 5 and 6 mm. Storefronts, railings, glass doors, and oversize lites often need 8 to 12 mm.

What decides the thickness

Four things drive the choice: the size of the pane, the wind load at the building's height and location, how far the glass is allowed to deflect, and the safety glazing rules for where it is installed. A long, narrow pane behaves differently from a square one of the same area. In Canada, glass is designed to CAN/CGSB-12.20, and the window or curtain wall designer usually sets the final thickness.

Thickness and tempering

Tempering makes glass roughly four times stronger than annealed glass of the same thickness, which can sometimes allow a thinner pane. But tempered glass cannot be cut or drilled afterwards, so every size, notch, and hole has to be final before it goes into the furnace. Order sizes carefully.

Why thick glass looks green

Look at the edge of a stack of glass and you will see the green get deeper as the glass gets thicker. That colour comes from small amounts of iron in the raw materials. Through the face of a 4 mm pane you barely notice it. Through a thick pane, or along its edge, the green becomes obvious. For display cases, exposed-edge railings, or anywhere colour accuracy matters, low-iron glass removes most of that tint and looks noticeably clearer.

Ordering from NAGC

We temper and fabricate glass in Guelph in sizes up to 11.5 ft x 8.2 ft, and tempered glass ships in 5 to 7 business days on average. Low-iron glass is available on request. Send your sizes and application, and we will confirm the right thickness with your quote.