Thermal Resistance Converter
Convert between thermal resistance units — K/W, °C/W, R-value (imperial), and more — instantly. Real-time conversion with copy-to-clipboard.
Thermal Resistance Converter
Enter a value in any unit — see the conversion in all others instantly.
How to Use the Thermal Resistance Converter
A building inspector measures the wall insulation as R-19 in imperial units but the energy audit report requires Kelvin per watt. A CPU heatsink datasheet lists thermal resistance as 0.5 K/W but the system design document uses degrees C per watt. Enter the value, pick the source unit, and the converter shows the equivalent in all four thermal resistance units.
A residential wall has an R-value of 19 in imperial units (degrees F times square feet times hours per BTU). The energy auditor needs the value in K/W for a European-standard report. Enter 19 in R-value and the converter shows 3.346 K/W. This conversion uses the factor 0.176110, which accounts for both the Fahrenheit-to-Kelvin and the square-foot-to-square-metre differences.
A CPU cooler specification lists 0.45 degrees C per watt. The thermal simulation software requires K/W. Enter 0.45 in degrees C/W and the result shows 0.45 K/W — identical because Celsius and Kelvin have the same degree size. The converter confirms this equivalence so you do not need to memorise which units are interchangeable.
A window manufacturer lists thermal resistance as 0.25 degrees F times square feet times hours per BTU. The HVAC design document requires the value in the per-watt format. Enter 0.25 in degrees F times h per BTU and the converter shows 0.528 K/W. The 0.527528 conversion factor handles the imperial-to-SI translation automatically.
A winter jacket is rated at 2.5 clo. The material science report requires the value in the standard SI unit. Since 1 clo equals 0.155 square metre kelvin per watt, a 2.5 clo jacket has a thermal resistance of 0.3875 square metre kelvin per watt. Enter 2.5 in clo and the converter shows the equivalent across all supported units.
How the Thermal Resistance Converter Works
The converter normalises every thermal resistance unit to Kelvin per watt (K/W) as the common base, then converts from that base to the target unit.
Unit Definitions
Kelvin per watt (K/W) is the base unit. Celsius per watt (degrees C/W) is identical to K/W because the degree sizes match. Fahrenheit per BTU per hour (degrees F times h per BTU) equals 0.527528 K/W. The imperial R-value (degrees F times square feet times hours per BTU) equals 0.176110 K/W and includes a square-foot-to-square-metre area conversion on top of the temperature conversion.
Conversion Formula
Each unit stores a factor relative to K/W. Converting from unit A to unit B follows: Result = Input x (FactorA / FactorB). For example, converting R-value 19 to K/W computes 19 x 0.176110 = 3.346 K/W. Converting the same R-value to degrees F times h per BTU computes 19 x (0.176110 / 0.527528) = 6.343 degrees F times h per BTU.
Relationship to Thermal Conductivity
Thermal resistance R is related to thermal conductivity k by the formula R equals thickness divided by k. A material with lower conductivity or greater thickness produces a higher R-value, meaning better insulation. For example, fibreglass with k equals 0.04 W per metre kelvin and a thickness of 0.2 metres has an R-value of 5 square metre kelvin per watt. This relationship lets you derive R-value from material properties or calculate required thickness for a target insulation level.
Frequently Asked Questions
What is thermal resistance (R-value)?
Thermal resistance measures a material's ability to resist heat flow. It is defined as the temperature difference across a material divided by the heat transfer rate. Higher thermal resistance means better insulation performance in building envelopes and thermal systems.
What is the difference between R-value and U-value?
R-value measures thermal resistance (how well a material blocks heat), while U-value measures thermal transmittance (how much heat passes through). They are inverses of each other: U = 1/R. A high R-value means good insulation, whereas a low U-value indicates the same.
What are typical R-values for wall insulation?
Typical residential wall insulation ranges from R-13 to R-21 depending on climate zone and wall construction. Roof and attic insulation generally requires higher values, often R-30 to R-60, to prevent heat loss in colder regions.
What is the difference between clo and tog?
Both clo and tog measure thermal insulation but for different applications. Clo is used for clothing insulation where 1 clo = 0.155 m²K/W. Tog is used for bedding and quilts where 1 tog = 0.1 m²K/W. Higher values in either scale indicate warmer insulation.
How do I convert between SI and Imperial R-value units?
To convert from SI (m²K/W) to Imperial R-value (ft²·°F·h/BTU), multiply by 5.678. To convert in the opposite direction, divide by 5.678. This converter handles these conversions automatically when you select the source and target units.
Why is thermal resistance important for energy efficiency?
Higher thermal resistance reduces heat transfer through walls, roofs, and floors, lowering heating and cooling energy demands. Proper insulation with adequate R-values helps maintain indoor comfort while minimizing energy consumption and utility costs.