PRT Calculator

Convert Resistance to Temperature

Calculate Temperature for Resistance Input

Temperature is calculated for the coefficient values shown below. You can enter calibration data to calculate custom coefficients and then use these values to convert ohms to Celsius, the resistance / temperature relationship is defined, for the range -200°C to 0°C Disclaimer

Rt=Ro[1 + At + Bt2 + C(t-100°C) t3] and for the range 0°C to 850°C Rt=Ro(1 + At + Bt2)


Calculate Custom Probe Coefficients

Use either standard values from IEC-60751 (default), enter values or enter a probes calibration data to calculate values for a particular probe. For this form you need two suitable temperature / resistance points and either the resistance at 0°C or 0.01°C. Entering a third temperature, below 0°C will allow the C coefficient to be calculated. This is only used for temperatures less than 0°C and both T3/R3 and C can be ignored for temperatures above 0°C

Select Ro or Rwtp

Enter either Ro (Resistance at 0°C) or Rwtp (Water Triple Point Value) to match selection


PRT Utility

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It can convert resistance values to temperature for 100-ohm platinum resistance thermometers, at best it will agree with IEC-60751 values to the order of 0.01C from -200 to 850C.

The default coefficients are those specified in IEC-60751 (2008). If you enter resistance / temperature data for a particular thermometer then probe specific coefficients can be calculated. The accuracy will vary for particular probes and the suitability of the user entered data.

After entering data you can store the information for subsequent visits to the page.


It is the responsibility of the user to ensure the validity of all calculated data. We accept no responsibility for any errors caused by inappropriate use, incorrect set up or any other cause; including defects in the software.
NO OTHER WARRANTIES, EXCEPT AS STATED ABOVE. The "web page" and documentation is provided "as is" without warranty of any kind and no other warranties (either expressed or implied) are made. We do not warrant, guarantee or make any representations regarding the use or results of the use of this utility or documentation and does not warrant that that operation will be error free.

In no event will the author, Isothermal Technology Ltd, its employees, agents or other associated people be liable for direct, indirect, incidental or consequential damages, expenses, lost profits, business interruption, lost business information or other damages arising out the use or inability to use.

Results with Default Coefficients

Input, Ohms Web Page Result, °C Expected, °C
18.52  -200.01  -200
39.72 -150.01 -150
60.26 -99.99 -100
80.31 -49.99 -50
100 0 0
119.4 50.01 50
138.51 100.01 100
157.33 150.01 150
175.86 200.01 200
194.1 250.01 250
212.05 300 300
229.72 350.01 350
247.09 399.99 400
264.18 450 450
280.98 500.01 500
297.49 550.01 550
313.71 600.01 600
329.64 650 650
345.28 699.99 700
360.64 750.01 750
375.7 799.99 800
390.48 850 850
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