R-Value to U-Value Calculator

Two ways of describing the same insulating property

R-value and U-value both describe how well a material resists heat flow, just expressed as reciprocals of one another - R-value describes resistance (higher is better insulation), while U-value describes the rate of heat transmission through the material (lower is better insulation).

Worked example

For standard R-13 wall insulation:

U-value = 1 / 13 = 0.077 BTU/(hr x sq ft x F)

R-Value	U-Value
R-13	0.077
R-19	0.053
R-38	0.026

Window and door ratings are almost always published as U-values directly rather than R-values, since U-value is the figure plugged straight into Manual J style heat load calculations without needing a conversion step.