How Thick Is Double Glazed Glass?

If you are comparing window quotes or planning an upgrade, it helps to understand what people really mean when they talk about how thick is double glazed glass. The answer is not just about one sheet of glass, but the total build up of the double glazing unit that sits inside your window frame.

What Double Glazing Thickness Actually Means

Before you can compare numbers, it is useful to know what makes up the thickness of a double glazed window and how suppliers describe it on plans and quotes.

The Parts Of A Double Glazed Unit (Glass, Spacer, Gap)

A modern double glazed unit, often called an insulated glass unit, is made up of three main parts:

• Two panes of glass
• A spacer bar that separates the panes around the perimeter
• A sealed air gap or inert gas cavity between the panes

Each glass pane is usually 3 mm or 4 mm thick in standard residential double glazed windows, although thicker glass is common where panes are larger or safety glass is required. The spacer creates an air gap, which is often filled with argon gas to improve thermal efficiency and reduce heat transfer.

How Thickness Is Written (For Example 4 / 12 / 4)

Double glazing thickness is normally written as three numbers in millimetres, for example 4 / 12 / 4.

• The first number is the thickness of the inner pane
• The middle number is the width of the air gap or spacer
• The last number is the thickness of the outer pane

So a 4 / 12 / 4 double glazed unit uses two panes of 4 mm float glass with a 12 mm gap. A 6 / 16 / 6 unit uses thicker glass and a wider gap, which increases total thickness and can improve thermal performance, sound reduction and security.

Typical Glass Thicknesses In Double Glazed Units

Homeowners often want to know what is standard and what is considered a higher performance or heavier option before they commit to new windows.

Common Pane Thicknesses (3 Mm, 4 Mm, 5 Mm, 6 Mm And Above)

In most homes, each glass pane in a double glazed unit is typically between 3 mm and 6 mm thick.

• 3 mm and 4 mm float glass are common in smaller windows
• 5 mm and 6 mm panes are used more often for larger glass panels, sliding doors and exposed locations
• Laminated glass and toughened glass are available from 6 mm upwards where extra safety or strength is needed

Using thicker glass panes improves acoustic performance and structural strength, and can be important in high wind zones or for ground floor safety glass.

Standard Double Glazing Build Ups Used In Homes

Most residential double glazing units fall into a small set of common build ups. These give a good balance between glass thickness, air gap and overall thickness.

Overall, the total thickness of a double glazed window unit typically ranges from about 14 mm up to 28 mm, with 24–28 mm very common in new energy efficient windows.

When Thicker Glass Is Used (Large Windows, Doors, Safety Zones)

You are more likely to see 6 mm, 8 mm or even 10 mm glass in:

• Large fixed glass panels and stacker doors
• Upper storey windows subject to higher wind loads
• Bushfire zones and pool fencing areas
• Locations where safety glass is required by code

In these cases, laminated glass or toughened safety glass is often specified as part of the double glazed unit to improve safety and security without sacrificing thermal efficiency.

How Thick Is The Gap Between The Panes?

The space between the two panes is just as important as the glass thickness when you are thinking about energy efficiency and comfort.

Typical Spacer And Gap Sizes (8 Mm, 10 Mm, 12 Mm, 16 Mm)

The gap between panes in double glazing normally ranges from 6 mm to 20 mm. Common spacer sizes are 8 mm, 10 mm, 12 mm and 16 mm.

A minimum space of 12 mm is recommended for optimum thermal performance, and 16 mm is a very common and effective size in modern double glazed units. The air gap is usually filled with air or argon gas, which acts as an insulating layer and helps limit the transfer of cold air into your home.

How Gap Thickness Affects Insulation

The sealed gap is a key part of the insulating barrier in double glazing.

• Narrow gaps still improve insulation compared to single glazing, but not as much as a 12–16 mm space
• Around 12–16 mm gives a strong balance of thermal efficiency and total unit thickness
• Very wide gaps can create convection currents in the air space, which reduces insulation and can work against your energy efficiency goals

If you want lower energy bills and more stable indoor temperatures, it is usually worth aiming for a quality double glazed unit with at least a 12 mm gap and argon gas where possible.

When A Wider Or Narrower Gap Makes Sense

A narrower gap can be useful in slim heritage frames or older window frame systems where there is limited depth to accept thicker double glazing. A wider gap, especially when combined with asymmetric glass thicknesses, can be very effective for noise reduction and can help with sound reduction on busy streets.

Is Your Double Glazing Thick Enough To Work Well?

Once you understand the basics, the next step is deciding whether the double glazing thickness you are being offered will deliver the performance you actually want.

Minimum Thickness For Basic Thermal Performance

Even a relatively thin double glazed unit, such as 4 / 10 / 4, will outperform single glazing for insulation. The second pane and the air gap provide added thermal resistance and reduce heat loss through the glass, which helps keep your house warm in winter and cooler in summer.

Thickness For Better Noise Reduction

If you are trying to control noise pollution from traffic, neighbours or nearby businesses, glass thickness matters more. Using different glass thicknesses in the same insulated glass unit, such as 6 mm on the outside and 4 mm on the inside, can disrupt sound waves and improve acoustic performance compared to two identical panes.

Extra Thickness For Safety And Security

Double glazing already improves security compared to single pane windows, because two panes of glass are harder to break than one. Where you want enhanced security or safety, increasing glass thickness or adding laminated glass to the double glazed unit makes it even more difficult for an intruder to force entry or for accidental impacts to cause damage.

Factors That Influence How Thick Double Glazed Glass Should Be

The ideal double glazing thickness for your home is not the same for every window. It depends on a mix of design, climate and compliance factors.

Window Size And Wind Load

Larger windows and doors tend to need thicker glass panes and sometimes thicker double glazing units to cope with wind load and prevent excessive flexing. Glaziers use maximum area tables and structural calculations to make sure each glass panel is strong enough for the opening size and location.

Climate And Energy Efficiency Goals

In hot summers and cool winters, thicker double glazing with a good air gap, low e coatings and argon gas can significantly improve thermal efficiency and reduce ongoing energy costs. If your goal is genuine energy efficiency rather than just ticking a box, it is often worth stepping up from the thinnest double glazing to a well specified unit around 24–28 mm total thickness.

Noise Levels Around Your Home

If you live near a main road, train line or flight path, noise reduction may drive your choice more than pure insulation. In these situations, thicker glass panes, a suitable air gap and possibly laminated glass can give you a noticeable drop in outside noise and a more comfortable living environment.

Safety, Bushfire And Building Code Requirements

Australian building codes, bushfire attack level ratings and safety glass rules all influence the glass thickness you can and should use. Ground floor windows, doors and certain wet areas may require laminated or toughened safety glass, which often starts from 6 mm and affects the total double glazing thickness that will fit in your frames.

How To Find Out The Thickness Of Your Double Glazed Glass

If you already have double glazed windows, it is useful to know how thick they are before you plan upgrades or compare new quotes.

Reading Markings Or Stamps On The Glass

Many insulated glass units have a small manufacturer stamp or etching in one corner that lists glass types, safety markings and sometimes thickness or build up. With a torch and a careful visual inspection around the edges, you can often confirm whether you have basic float glass, laminated glass or low e glass and get a rough sense of thickness.

Using Simple Glass Thickness Gauges

Glazing professionals use small glass thickness gauges or digital tools that sit against the pane and use reflections to calculate glass thickness and air gap. These are designed for already installed windows and are a quick way to measure double glazing thickness without removing the sash or disturbing the sealed unit.

When To Ask A Glazier Or Installer To Check

If you are unsure whether your current double glazed units are thick enough for your needs, or you suspect single glazing in some older rooms, it is worth asking a glazier or window installer to take a look. A professional assessment will confirm glass thicknesses, air gaps and gas fill, and can highlight any failed units where moisture has entered the space between panes.

Thicker Double Glazing Vs Standard Thickness

Homeowners often ask whether they should choose the thickest possible double glazing or stick with standard units. The answer depends on where the window sits and what you are trying to solve.

When Thicker Glass Brings Real Benefits

Thicker double glazing makes the most sense where your home faces specific challenges. Street facing rooms that cop a lot of noise, large doors that take a beating from wind, or spaces where you want high security all benefit from thicker glass and a well designed air gap. In these locations you are more likely to notice the performance difference every day.

Weight, Cost And Hardware Considerations

The trade off is that thicker glass and wider air gaps increase weight and cost. Heavier double glazed units need stronger window frames and hardware, and installation takes more care and time. That is why it often makes sense to reserve the heaviest units for problem elevations and use more standard double glazing in quieter or less exposed parts of the house.

Balancing Performance, Budget And Appearance

Very thick double glazing can change the look of some frames, which may not suit traditional homes or fine timber sections. A good glazing designer will help you mix and match double glazing thicknesses across the home so you get the benefits where they matter most while keeping appearance, cost and weight under control.

Choosing The Right Double Glazing Thickness For Your Home

The right answer on thickness is always specific to your house, your climate and your priorities, rather than a single number that suits everyone.

Bedrooms, Living Areas And Street Facing Rooms

As a rule, it pays to put your best performing double glazed windows into bedrooms, main living areas and any room that faces traffic or strong sun. This is where added thermal resistance, noise reduction and reduced condensation will have the most impact on comfort and lower energy bills.

Matching Thickness To Frame Type And Window Style

Different window frame systems have different limits on the double glazing thickness they can accept. uPVC, thermally broken aluminium and timber frames all have their own maximum unit thickness and weight ratings. Sliding doors, awning windows, casements and fixed panels also place different loads on hardware, so it is important to match glass thickness to the frame and opening style.

Questions To Ask Your Window Or Glazing Supplier

When you are comparing options, ask your supplier:

• What exact double glazing thickness are you proposing for each window and door?
• What are the glass thicknesses and air gap in each insulated glass unit?
• How will that specification affect energy efficiency, noise reduction and safety in this home?
• Are there thicker or thinner alternatives if I want to fine tune performance or budget?

Ready To Talk About Double Glazing Thickness For Your Home?

Double glazing thickness can feel technical, but getting it right makes a real difference to everyday comfort, noise reduction and energy efficiency. You do not need to be a glazing expert to make a good choice, as long as you understand the basics of how pane thickness and gap size affect performance in your climate.

By matching glass thickness to your window size, noise levels and safety needs, you can improve insulation, reduce energy costs and create a more comfortable home in both summer and winter. To make the process easier, browse our Trade Heroes directory to find trusted double glazing specialists near you, compare options and get quotes for the right double glazing thickness for your home and budget.