# Thermal resistance unit

Referring to the Infineon ICE2A365 datasheet.

In the datasheet, the thermal resistance from junction to ambient is 90 K/W.

What is K? Is it kelvin or degrees C.

If it is kelvin than changing it to degrees centigrade will be approx -183C/W, which does not make any sense. The only difference between them is the zero value (position of origin). Notice that the difference between any two points is the same on both the scales. So 1°C rise in temperature means 1K rise in temperature.

1 degree C is equivalent to 1 degree K.

See image: The SI units of thermal resistance are kelvins per watt or the equivalent degrees Celsius per watt (the two are the same since the intervals are equal: Δ1 K = Δ1 °C).

As both answers above are true, they are missing the zero (0) reference points: - For °C (Celsius or "Centigrade") scale the 0 reference point is the freezing temperature of water. The °C value can be either positive or negative as needed. - For °K (Kelvin) scale the 0 reference point is the "absolute zero" temperature as follows: "By international agreement, absolute zero is defined as precisely 0 K on the Kelvin scale, which is a thermodynamic (absolute) temperature scale and –273.15 degrees Celsius on the Celsius scale." The °K value can only be positive.

For both °C and °K scales the difference between any two measured temperatures is exactly the same, for instance 1°C difference = 1°K difference.

I was taught that 1 degree centigrade is an actual temperature and 1 centigrade degree is an increment of one degree. This avoids confusion. J Garrioch.