Window U-Value Calculator & Converter

Convert between U-values (Imperial & Metric) and R-values. Understand thermal efficiency for glazing.

Convert Ratings

Typical double-pane is ~0.30

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Understanding Window Efficiency

Windows are the weakest thermal link in most buildings. While a basic insulated wall might be R-20, a standard single-pane window is only R-1. Even top-tier triple-pane windows rarely exceed R-7.

U-Value vs. R-Value

  • U-Value (U-Factor): Measures the rate of heat loss. Lower is better. It is the standard rating for windows and doors.
    Formula: U = 1 / R
  • R-Value: Measures resistance to heat flow. Higher is better. It is the standard rating for insulation (fiberglass, foam).
    Formula: R = 1 / U

Common Ratings

  • Single Pane: U-1.00 (R-1)
  • Double Pane (Clear): U-0.50 (R-2)
  • Double Pane (Low-E + Argon): U-0.30 (R-3.3)
  • Triple Pane: U-0.18 to U-0.24 (R-4 to R-5.5)

5 Fun Facts About Windows

Invisible Metal

Low-E coatings are silver layers thinner than a human hair. They reflect heat like a mirror but let light pass through.

Tech

Heavy Gas

Argon and Krypton are used between panes because they are denser than air, slowing down convective heat loops.

Chemistry

Condensation

The edge of the glass is coldest. Warm-edge spacers (silicone/foam) replace aluminum spacers to stop water forming.

Physics

Solar Gain

SHGC (Solar Heat Gain Coefficient) measures free solar heat. In cold climates, high SHGC cuts heating bills.

Passive Solar

Heat Mirror

Some windows use a suspended plastic film between panes instead of a third glass layer to be lighter.

Innovation

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