Temperature Measurement · Glossary

What are Temperature Scales?

°C, K, °FTemperature Measurement

Temperature scales are the units used to state temperature: Celsius and Fahrenheit for everyday use, and kelvin for absolute temperature.

Temperature Scales Explained

The kelvin is the SI unit and starts at absolute zero. A temperature difference of 1 K equals 1 °C. Gas law, radiation and many engineering formulas need absolute temperature in kelvin.

Fahrenheit is still used in US data sheets. Rankine is the absolute scale with Fahrenheit sized degrees.

Temperature Scales Formula

T(K) = t(°C) + 273.15 and t(°F) = t(°C) × 9 ÷ 5 + 32

T	absolute temperature in kelvin
t	temperature in °C or °F

Example: 25 °C = 298.15 K = 77 °F.

Calculators for Temperature Scales

CalculatorTemperature Transmitter CalculatorFree online calculator with formula and worked example.CalculatorGas Law CalculatorFree online calculator with formula and worked example.

Free Downloads

Free downloadTemperature Measurement Cheat SheetFree printable PDF cheat sheet.

Frequently Asked Questions

What are Temperature Scales?

Temperature scales are the units used to state temperature: Celsius and Fahrenheit for everyday use, and kelvin for absolute temperature.

Is it degrees kelvin?

No. Write kelvin or K without the degree sign.

When must kelvin be used?

In any formula that multiplies or divides by temperature, such as gas laws and radiation, not just for differences.

Learn more on the blog

What is an RTD and how it works

A practical guide on instrumentationblog.in with more detail on temperature scales and how it is applied on real plants.

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More Temperature Measurement Terms

Temperature termPt100Pt100 is a platinum RTD with a resistance of 100 Ω at 0 °C, following the IEC 60751 resistance curve.Temperature termAlpha CoefficientAlpha coefficient is the average change in RTD resistance per degree between 0 and 100 °C, divided by the…Temperature termRTD Wiring (2, 3 and 4 Wire)RTD wiring is the 2, 3 or 4 wire connection of an RTD; more wires cancel more of the lead wire resistance.Temperature termRTD Self HeatingRTD self heating is the rise in sensor temperature caused by the measuring current flowing through the…Temperature termRTD Tolerance ClassRTD tolerance class is the permitted deviation of an RTD from the standard curve, set by IEC 60751 as…Temperature termSeebeck EffectThe Seebeck effect is the voltage generated in a conductor along which there is a temperature gradient;…

All temperature measurement terms · Full glossary A to Z