Window U-Value Calculator

Calculate overall window U-factor from center-of-glass, edge-of-glass, and frame components using area-weighted average.

Overall window width
inches
Overall window height
inches
Single pane: ~1.0, Double low-e: ~0.25-0.30, Triple: ~0.15-0.20
Btu/(h·ft²·°F)
Typically 10-30% higher than center-of-glass
Btu/(h·ft²·°F)
Vinyl: ~0.3-0.5, Aluminum: ~1.0-2.0, Fiberglass: ~0.2-0.4
Btu/(h·ft²·°F)
Typical: 2.5 inches from frame
inches
Frame width on all sides
inches

Results

Total Window Area-ft²
Center-of-Glass Area-ft²
Edge-of-Glass Area-ft²
Frame Area-ft²
Overall Window U-Factor-Btu/(h·ft²·°F)
References: NFRC 100 - Procedure for Determining Fenestration Product U-factors, ASHRAE Fundamentals Ch. 15