Instrumentation
RTD Calculator
Pt100/Pt1000 use the IEC 60751 Callendar-Van Dusen equation. Ni100/Cu100 use published approximations.
Standard method — stated scope limits apply
Inputs
Resistance → Temperature
Temperature → Resistance
Enter values and calculate.
About This Calculation
An RTD (Resistance Temperature Detector) measures temperature from the predictable way a pure metal’s electrical resistance rises with temperature. Platinum is the standard choice (Pt100 = 100Ω at 0°C) because its resistance-temperature relationship is extremely stable and repeatable, and it doesn’t drift or oxidize the way cheaper metals do. The relationship isn’t perfectly linear, so accurate conversion uses the Callendar-Van Dusen equation rather than a straight-line approximation — the error from assuming linearity grows the further you are from 0°C.
Frequently Asked Questions
What is the difference between 2-wire, 3-wire, and 4-wire RTD wiring?
2-wire includes the lead-wire resistance as measurement error and should only be used for short runs where that error is acceptable. 3-wire (the most common industrial choice) compensates for lead resistance assuming both leads match. 4-wire eliminates lead resistance error entirely and is used where the highest accuracy is needed.
Why use an RTD instead of a thermocouple?
RTDs are generally more accurate and stable over time, and don’t need cold-junction compensation. Thermocouples respond faster, tolerate much higher temperatures, and are cheaper — the choice usually comes down to required accuracy and temperature range.
What does the accuracy class (Class A, Class B) mean?
These are tolerance bands defined in IEC 60751: Class B (±0.30°C at 0°C, widening with temperature) is the common industrial grade; Class A (±0.15°C at 0°C) is tighter and used where accuracy matters more.
Can an RTD be used at very high temperatures?
Standard Pt100 elements are typically rated to around 600–850°C depending on construction, well below what thermocouples can reach (some types exceed 1700°C) — for very high-temperature service a thermocouple is usually the better fit.