What is the standard DGU thickness for UK double glazing?

The most common DGU make-up in the UK is 4/16/4 (4mm glass, 16mm cavity, 4mm glass) giving a total thickness of 24mm. This is optimum for argon-filled units. Heritage or slim units may use 4/6/4 (14mm total) or 4/8/4 (16mm total) for restricted rebate depths.

How much does a double glazed unit weigh?

A standard 4/16/4 DGU weighs approximately 20 kg per square metre (glass only, not including the frame). A typical 1200mm x 1200mm unit weighs about 28.8 kg. Units with thicker glass, laminated panes or triple glazing weigh proportionally more. Glass density is 2,500 kg per cubic metre.

What rebate depth do I need for double glazing?

Rebate depth must accommodate the DGU thickness plus sealant/glazing tape depth (typically 5-8mm) and a small tolerance (2mm). For a standard 24mm DGU, you need a minimum rebate depth of around 32mm. Always check the frame manufacturer specifications as these vary between profiles.

Can I replace single glazing with DGUs in existing frames?

Existing timber frames may have rebates as shallow as 15mm, which is too shallow for standard DGUs. Slim heritage units (14-16mm) may fit with modifications. The rebate must be deep enough and the frame strong enough to support the additional weight. A FENSA-registered installer should assess suitability.

What is the maximum size for a sealed double glazed unit?

Maximum DGU size depends on glass thickness and handling weight. Typical practical limits are approximately 3000mm x 2000mm for 4mm glass and larger for thicker glass. Very large units may require toughened glass for wind load resistance. Most UK glass suppliers limit individual pane weight to around 100-120 kg for standard delivery.

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Double Glazing Unit Calculator — Thickness, Weight & Rebate Depth

Calculate sealed unit thickness, weight and rebate depth required for double glazed units. Essential for specifying frames and assessing handling requirements.

Pane 1 Thickness (outer)

Outer pane facing the weather

Cavity Width

16mm is optimal for argon fill

Pane 2 Thickness (inner)

Inner pane facing the room

Number of Units

Total DGUs to produce or order

Unit Width

Width of the sealed unit (not the frame)

Unit Height

Height of the sealed unit

How We Calculate This

This calculator determines the overall DGU thickness, unit weight and rebate depth required from the pane thicknesses, cavity width and unit dimensions.

The formulas

Total thickness = Pane 1 + Cavity + Pane 2

Weight = Area × Thickness (m) × 2,500 kg/m³ (per pane)

Rebate depth = Total thickness + Sealant depth + 2mm tolerance

Common DGU make-ups

4/16/4 (24mm) — standard argon-filled unit
4/12/4 (20mm) — common for air-filled units
6/16/6 (28mm) — acoustic or toughened glass
4/6/4 (14mm) or 4/8/4 (16mm) — slim/heritage units

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.