Glazing Uvalue to Rvalue Calculator
Calculate glazing uvalue rvalue accurately for your build. Get material quantities, waste allowances, and project cost breakdowns.
Reviewed by Abdullah, Technical Content Specialist
Formula
R-value = 1 / U-value | Q = U ร A ร ฮT
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/hrยทftยฒยทยฐF. The window is 15 sq ft, indoor temp 70ยฐF, outdoor temp 25ยฐF. Calculate R-value and heat loss.
Solution:R-value = 1 / U = 1 / 0.30 = 3.333\nMetric U-value = 0.30 ร 5.678 = 1.703 W/mยฒยทK\nฮT = 70 - 25 = 45ยฐF\nHeat loss = U ร A ร ฮT = 0.30 ร 15 ร 45 = 202.5 BTU/hr\nDaily loss = 202.5 ร 24 = 4,860 BTU = 1.42 kWh\nMonthly cost โ 1.42 ร 30 ร $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, 70ยฐF inside, 10ยฐF outside.
Solution:Single-pane: R = 1/1.10 = 0.909\n Heat loss = 1.10 ร 20 ร 60 = 1,320 BTU/hr\nTriple-pane: R = 1/0.18 = 5.556\n Heat loss = 0.18 ร 20 ร 60 = 216 BTU/hr\nSavings = 1,320 - 216 = 1,104 BTU/hr\nDaily savings = 26,496 BTU = 7.77 kWh\nSeasonal savings โ $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/hrยทftยฒยทยฐF (imperial) or W/mยฒยทK (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.
References
Reviewed by Abdullah, Technical Content Specialist ยท Editorial policy