How the weight is worked out
The area in square metres is multiplied by the thickness in millimetres, then by 2.5. A one metre square pane of 6 mm glass is 1 times 6 times 2.5, which is 15 kg.
The figure holds because glass density is about 2,500 kg per cubic metre. A millimetre of thickness over a square metre is a litre of glass, and a litre weighs 2.5 kg.
Multiple panes are multiplied at the end, which is what a glazier needs for a delivery.
Worked example
A one metre square pane of 6 mm glass weighs 15 kg. The same pane in 4 mm is 10 kg, and in 10 mm it is 25 kg.
A double glazed unit is the two panes plus the spacer and the gas, so a 4 mm unit weighs about 20 kg per square metre before the frame.
Why the weight matters
Two people can lift about 25 kg each comfortably. A 2 m by 1 m pane of 10 mm glass is 50 kg, which is a two person lift with suckers and a plan.
The weight also decides the fixings. A mirror or a splashback needs an adhesive and a mechanical fixing rated for the mass, not just the area.
Toughened glass is the same density as annealed, so the weight does not change with the heat treatment.
Limits of this calculator
It uses the density of soda-lime float glass. Leaded, borosilicate and laminated glass differ, and laminated adds the interlayer.
It does not include the frame, the spacer bar or the gas in a sealed unit.
It does not check whether the glass is strong enough for the span, which is a separate structural question.
For the frame that carries it, use the steel weight calculator.
Inputs for the glass weight calculator
Pane width
Width of one pane in metres.
Pane height
Height of the same pane in metres.
Glass thickness
Thickness in millimetres, 4 mm for single glazing and 6 mm for a table top.
Number of panes
How many panes of this size, for a delivery or a total weight.
CALCULATOR QUESTIONS
Glass weight calculator questions
How much does 6 mm glass weigh?
15 kg per square metre. Each millimetre of thickness adds 2.5 kg per square metre.
How heavy is a double glazed unit?
About 20 kg per square metre for a 4 mm unit, before the frame.
Is toughened glass heavier?
No. The density is the same, so the weight depends only on size and thickness.
Can one person lift a large pane?
Not safely above about 25 kg. Use two people and suckers, and plan the route before lifting.