Glazing Uvalue to Rvalue Calculator
Calculate glazing uvalue rvalue accurately for your build. Get material quantities, waste allowances, and project cost breakdowns.
Formula
R-value = 1 / U-value | Q = U × A × ΔT
R-value is the reciprocal of U-value, measuring thermal resistance. Heat loss Q is calculated by multiplying U-value by window area and the temperature difference between indoors and outdoors.
Worked Examples
Example 1: Double-Pane Low-E Window Analysis
Problem: A double-pane low-e window has a U-value of 0.30 BTU/hr·ft²·°F. The window is 15 sq ft, indoor temp 70°F, outdoor temp 25°F. Calculate R-value and heat loss.
Solution: R-value = 1 / U = 1 / 0.30 = 3.333\nMetric U-value = 0.30 × 5.678 = 1.703 W/m²·K\nΔT = 70 - 25 = 45°F\nHeat loss = U × A × ΔT = 0.30 × 15 × 45 = 202.5 BTU/hr\nDaily loss = 202.5 × 24 = 4,860 BTU = 1.42 kWh\nMonthly cost ≈ 1.42 × 30 × $0.13 = $5.55
Result: R-value = 3.33 | Heat loss = 202.5 BTU/hr | Monthly cost = ~$5.55
Example 2: Single-Pane vs Triple-Pane Comparison
Problem: Compare a single-pane (U=1.10) vs triple-pane (U=0.18) window, both 20 sq ft, 70°F inside, 10°F outside.
Solution: Single-pane: R = 1/1.10 = 0.909\n Heat loss = 1.10 × 20 × 60 = 1,320 BTU/hr\nTriple-pane: R = 1/0.18 = 5.556\n Heat loss = 0.18 × 20 × 60 = 216 BTU/hr\nSavings = 1,320 - 216 = 1,104 BTU/hr\nDaily savings = 26,496 BTU = 7.77 kWh\nSeasonal savings ≈ $151
Result: Single: 1,320 BTU/hr | Triple: 216 BTU/hr | 83.6% reduction
Frequently Asked Questions
What is the difference between U-value and R-value for glazing?
U-value and R-value are inverse measurements of thermal performance in windows and glazing. U-value (also called U-factor) measures the rate of heat transfer through a material, expressed in BTU/hr·ft²·°F (imperial) or W/m²·K (metric). A lower U-value indicates better insulation, meaning less heat escapes. R-value measures thermal resistance, which is simply the reciprocal of U-value (R = 1/U). A higher R-value indicates better insulation. For example, a window with a U-value of 0.30 has an R-value of 3.33, meaning it provides moderate insulation. The construction industry historically uses U-values for windows and R-values for wall and attic insulation, though both describe the same physical property from opposite perspectives. The National Fenestration Rating Council (NFRC) rates windows primarily by U-factor in the United States.
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Does Glazing Uvalue to Rvalue Calculator work offline?
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How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.