Below is the Capgo RTD Calculator. To use it you need a browser that supports Java applets.

• select your preferred temperature units
• select a predefined RTD type (e.g. Pt385)
• enter the RTD's resistance at 0°C
• enter the RTD's resistance at the temperature of interest in the same resistance units as the Ro field
• click calculate

The so called Pt100 is by far the most commonly used RTD type, it is usually of the Pt385 material with 100 ohm resistance at 0°C.