Glass Thickness Converter

Understanding Glass Thickness Measurements

Glass thickness is specified in millimeters in most of the world but in fractional inches in the United States. Converting between these systems is essential when ordering glass, specifying glazing for construction projects, or comparing products from different manufacturers. Glass weight calculations are important for structural support design and shipping estimates.

Standard Glass Thicknesses:

Glass is manufactured in standard thicknesses. The nominal sizes do not always convert to exact fractions, and the fraction the trade uses is not always the mathematically nearest one:

Those two fraction columns matter more than they look. 6 mm glass is sold as quarter-inch, and every glazier will call it that, but a true quarter inch is 6.35 mm. The glass is 15/64", one 64th under the name on the invoice. That 0.35 mm is nothing in a rubber-gasketed frame and quite a lot in a channel machined to a nominal 1/4".

The rounding does not always go that way, which is the part that catches people. 10 mm is sold as 3/8", but 3/8" is only 9.53 mm, so that sheet is nearly half a millimetre thicker than its name. Cut a 3/8" groove for 10 mm glass and it will not go in. The calculator tells you which direction the gap runs for whichever thickness you enter.

Weight Calculation Formulas:

Standard float glass has a density of approximately 2,500 kg/m³ (156 lb/ft³):

Weight per sq ft (lb) = thickness (inches) × 13.0 Weight per sq m (kg) = thickness (mm) × 2.5

Or more precisely: Weight (kg/m²) = thickness (mm) × 2.5 Weight (lb/ft²) = thickness (mm) × 0.512

Glass Weight Reference:

Practical Examples:

• A standard residential window uses 3 mm (1/8 inch) double-strength glass, weighing about 1.54 lb per square foot (7.5 kg per square meter).
• A frameless shower door typically uses 3/8 inch (10 mm) tempered glass, weighing 5.12 lb/sq ft. A standard 30"×72" shower panel comes out at 77 pounds (35 kg), which is why they ship on edge and why hinges for them are sold by weight rating.
• A 4 ft × 8 ft glass tabletop in 1/2 inch (12 mm) glass weighs approximately 197 lb (89 kg).
• Laminated glass (two layers bonded with a PVB interlayer) weighs about the same as monolithic glass of the same total thickness. The thin plastic interlayer is lighter than glass, so 6.38 mm laminated comes out within a few percent of 6 mm float glass.

Tips:

• Tempered glass is the same thickness as regular glass but is 4-5 times stronger. The thickness does not change during the tempering process.
• Insulated glass units (IGUs or double-pane windows) use two panes separated by an air or gas gap. A typical IGU might be 3mm + 12mm gap + 3mm = 18mm total thickness.
• For safety glazing in doors and low windows, building codes require tempered or laminated glass. The codes regulate the glass type, not a minimum thickness; 4-5 mm tempered is common in framed doors, while frameless shower panels typically use 6-10 mm.
• When shipping glass panels, account for packing materials adding 20-30% to the glass weight alone.