Calculation reviewed: 4 October 2026 · Engineering Desk Tools
How to use the Pt100 / Pt1000 RTD resistance and temperature calculator
Convert between RTD resistance and temperature using the standard Callendar–Van Dusen equation. Start with measurements or documented values for the equipment and reporting period you actually want to assess. The calculator does not fill in a typical installation for you. Its blank fields help keep a demonstration value from being mistaken for your own operating data.
Choose the required options, enter the values in the labelled units and select Calculate. If a field is rejected, check its range and unit before changing it. The result is accompanied by the equation and assumptions so you can decide whether it answers your engineering question.
Inputs and measurement basis
- Conversion. Choose whether you are entering a temperature or a measured resistance.
- Sensor type. Pt100 is 100 Ω at 0 °C and Pt1000 is 1000 Ω. Check the sensor label or data sheet.
- Temperature (°C) or resistance (Ω) for the selected conversion. Temperature in °C (−200 to 850) or resistance in Ω, matching the sensor type and conversion chosen above.
Record the measurement source and operating condition. Retain unrounded values for verification.
Method and interpretation
A platinum RTD changes resistance with temperature in a smooth, repeatable way described by the Callendar–Van Dusen equation. A Pt100 reads 100 Ω at 0 °C and about 138.5 Ω at 100 °C; a Pt1000 gives ten times those values. Above 0 °C the relationship is a quadratic, so the inverse has a closed form. Below 0 °C a fourth-order term is needed and the inverse is solved numerically.
For T ≥ 0 °C: R = R0 × (1 + A·T + B·T²). For T < 0 °C: R = R0 × (1 + A·T + B·T² + C·(T − 100)·T³). A = 3.9083×10⁻³, B = −5.775×10⁻⁷, C = −4.183×10⁻¹² (IEC 60751, α = 0.00385).
Valid from −200 °C to 850 °C for a platinum RTD with α = 0.00385. The result is the ideal nominal value; tolerance class (A, B, AA), self-heating, lead-wire resistance in 2-wire circuits and transmitter accuracy are not included. Enter resistance measured at the sensor, not the resistance of the wiring. Resistance to temperature below 0 °C is solved numerically.
Worked example
This example does not populate the form. Enter your own installation data.
Calculated result: 138.5055 Ω. Nominal resistance of a standard platinum RTD. Tolerance class and wiring are not included.
Check the arithmetic independently using the displayed equation. Retain intermediate precision and compare the final value with your equipment documentation.
Quick-reference table
These are illustrative values, not certified ratings or manufacturer data. Use the form for your own conditions.
Common mistakes
Using a two-wire reading without allowing for lead resistance; mixing Pt100 and Pt1000; applying a thermocouple or NTC table; ignoring the sensor tolerance class; measuring resistance with the sensor still connected to a live loop. Before relying on the output, check the decimal format, unit scale and source of each value. Recheck unusual results against the formula.
Frequently asked questions
Are the example values used automatically?
No. Inputs remain blank when the tool opens or when you clear them. The worked example and table are reading material below the calculator. Enter the actual values you want to check each time, and label saved reports so their context is not lost.
What does the result mean?
The result is the nominal resistance or temperature for a standard platinum RTD. If a measured value differs from it, check wiring, lead resistance, sensor type and tolerance class before suspecting the sensor.
Can I use a zero or a negative value?
The allowed range follows the meaning of each input. A divisor needs a positive value; other fields may allow zero. Check the form labels and error message rather than forcing an invalid value. A rejected input must be corrected before a result can be shown.
Is this a final design or equipment approval?
No. Valid from −200 °C to 850 °C for a platinum RTD with α = 0.00385. The result is the ideal nominal value; tolerance class (A, B, AA), self-heating, lead-wire resistance in 2-wire circuits and transmitter accuracy are not included. Enter resistance measured at the sensor, not the resistance of the wiring. Resistance to temperature below 0 °C is solved numerically. Use the calculation as support for a checked decision, and review equipment documentation and applicable requirements before changing an installation or operating setting.
How can I save or share a calculation?
Calculate first, then use Copy result or Print report. Some maintenance tools also provide a CSV summary. Reports contain your own entered data, so review them before sharing. You can share the public page URL without including plant records or confidential measurements.
How do I report an unexpected result?
Use the Contact page and include the tool URL, input values, units, expected output and the reference you used. Explain the measurement basis. Exclude confidential information.
Related tools and records
Use related calculations with consistent units, periods and equipment scope.
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