Insulated Glass Unit Calculator

IGU specifications from thermal and condensation requirements.

Outer pane (mm)

Inner pane (mm)

3rd pane (mm, 0=double)

Gap 1 width (mm)

Gap 2 width (mm)

Gas fill

Low-E coatings

Tab to move between fields

U-value (W/m²K)

2.86

R-value (m²K/W)0.35

R-value (imperial)1.99

SHGC (estimate)0.74

Condensation resistance64

Total IGU thickness (mm)20

Weight (kg/m²)20

How to Use This Calculator

Enter outer pane, inner pane (and third pane if triple glazing) thicknesses in mm.
Enter Gap 1 and Gap 2 widths in mm and select the Gas Fill: air, argon, krypton, or xenon.
Enter the number of Low-E coatings (0–3) applied to the glass surfaces.
Review U-Value in W/m²K and R-Value — lower U-values indicate better thermal insulation.
Check SHGC, Condensation Resistance, and Total IGU Thickness for specification compliance.

How the result changes with Gap 1 width (mm)

Outer pane (mm): Outer glass pane thickness in mm.
Inner pane (mm): Inner glass pane thickness in mm.
3rd pane (mm, 0=double): Third pane thickness for triple glazing. Enter 0 for double glazing.
Gap 1 width (mm): Spacer gap width between pane 1 and 2. Typically 12 or 16 mm.
Gap 2 width (mm): Second gap width for triple glazing.
Gas fill: 0 = Air, 1 = Argon, 2 = Krypton, 3 = Xenon.
Low-E coatings: Number of low-emissivity coatings (0 to 3).

U-value (W/m²K): Center-of-glass thermal transmittance. Lower is better. Code limit often 1.4-1.8 W/m²K.
R-value (m²K/W): Thermal resistance in SI units.
R-value (imperial): Thermal resistance in ft²·°F·h/BTU.
SHGC (estimate): Solar Heat Gain Coefficient — fraction of solar energy transmitted.
Condensation resistance: Condensation Resistance Factor (0-100). Higher is better.
Total IGU thickness (mm): Overall thickness of the insulated glass unit.
Weight (kg/m²): Glass-only weight per square meter (excludes spacer/sealant).

Identify Input Parameters
4 parameters
Outer pane (mm) = 4, Inner pane (mm) = 4, 3rd pane (mm, 0=double) = 0, Gap 1 width (mm) = 12 = 7 input(s) provided
Calculate U-value
U-value = 1 / R_total
2.855 = 2.855
Calculate R-value
R-value = R_total
0.35 = 0.35
Calculate R-value
R-value = R_total * 5.678
1.99 = 1.99