# Celsius vs. Kelvin: When it does and doesn't matter **URL:** \ **Category:** Digikey.com Navigation and Terminology\ **Tags:** tech-tips, terminology\ **Created:** [August 7, 2017, 5:00am UTC](https://forum.digikey.com/t/celsius-vs-kelvin-when-it-does-and-doesnt-matter/411 "2017-08-07T05:00:00Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![rick\_1976](https://sea2.discourse-cdn.com/digikey/user_avatar/forum.digikey.com/rick_1976/32/1571_2.png) [@rick\_1976](https://forum.digikey.com/u/rick_1976)\ **Post date:** [August 7, 2017, 5:00am UTC](https://forum.digikey.com/t/celsius-vs-kelvin-when-it-does-and-doesnt-matter/411/1 "2017-08-07T05:00:00Z")
While the Kelvin and Celsius (or centigrade, if one prefers that name) scales are indeed different, they differ only by an offset; the interval or change in a physical quantity represented by 1 degree in either scale is identical. If temperature scales were rulers, the distance between marks on a Kelvin ruler and a Celsius ruler would be identical. ![image](https://global.discourse-cdn.com/digikey/original/1X/0b7efe3f729df1e8b85f3062a74a24ebb64e79a7.png) Because the increment represented by one degree in either scale is exactly the same, in the context of temperature _ **changes** _ or _ **differences** _ it’s perfectly fine to use °K or °C interchangeably, because there is absolutely no difference. If the weather forecast says tomorrow’s high temperature will be 2°C or 2°K _warmer than today_, it means exactly the same thing because a temperature _change_ is being referenced. On the other hand, an outdoor temperature of 30°C is pleasant or maybe a bit warm, while an outdoor temperature of 30°K would be uncomfortably cold (Oxygen freezes into a solid @ about 54°K). The distinction between scales matters in the latter case, because what’s being referenced is an _absolute_ quantity; a measurement made relative to some physical reference point where “zero” actually means “zero” in a sense of nothingness, vacuity, or a complete and total absence. When temperatures are mentioned in the electronics field, there are some cases when a temperature _change_ or _difference_ is being talked about, and some other cases where an _absolute_ quantity is being referenced. Resistor temperature coefficients are an example of the first case. When a resistor datasheet specifies a temperature coefficient of +/- 100ppm/°K for example, what that means is that for every 1°K _change_ in device temperature, the measured resistance of a device may _change_ by 100 parts per million in either direction from the initial measured value. Because the quantity in question is describing the effects of a _change_ in temperature and a _change_ of 1°C is exactly equivalent as a _change_ of 1°K, the units of °C and °K can be used interchangeably with no difference in meaning in this case, and use of either one is simply a matter of preference. Different suppliers have different preferences; some resistor manufacturers specify temperature coefficients in terms of °C, others in °K. One of our goals at DigiKey is to present the products we sell in a way that helps our customers make apples-to-apples comparisons between similar products, and find similar products to compare with a minimum amount of mouse-clicking. Part of that process is eliminating distinctions without a difference, and because there’s no practical difference between a resistor temperature coefficient of (x) per °C and (x) per °K, we’ve chosen to eliminate that distinction. An example of where the use of °C or °K often does matter is in the context of temperature sensors. Semiconductor temperature sensors can be calibrated to deliver outputs that are proportional to either °C or °K (or °F, or °R, for that matter) so if such a device has an output equation of 10mV/°(x), the difference between (x) being °C or °K would mean a difference in sensor output of 2.73V at a given temperature. Other devices such as thermistors have non-linear temperature characteristics, making it numerically important to use the right temperature scale in one’s calculations. ---
**Author:** ![md2020](https://avatars.discourse-cdn.com/v4/letter/m/dec6dc/32.png) [@md2020](https://forum.digikey.com/u/md2020)\ **Post date:** [March 23, 2020, 11:43am UTC](https://forum.digikey.com/t/celsius-vs-kelvin-when-it-does-and-doesnt-matter/411/2 "2020-03-23T11:43:27Z")
Hello Rick, Thanks for your article. However, it would have been better, I think, if you used Kelvin without degrees. As you may know, the unit is just K, not °K ([https://en.wikipedia.org/wiki/Kelvin](https://en.wikipedia.org/wiki/Kelvin)). Best regards, Marcus