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Instrumentation

RTD Temperature Calculator

A platinum RTD (Resistance Temperature Detector) changes resistance with temperature. This calculator uses the simple linear approximation R = R₀(1 + αT) to convert between measured resistance and temperature. It supports Pt100 (R₀ = 100 Ω) and Pt1000 (R₀ = 1000 Ω) sensors with the standard alpha of 0.00385 1/°C.

TypeInteractive calculator — separate from unit conversions

Calculator

Ω
1/°C
Result
Temperature50 °C

Linear approximation — R = R₀(1 + αT). Not full IEC 60751.

Formulas

Resistance from temperature
R = R₀ × (1 + α × T)
Temperature from resistance
T = (R / R₀ − 1) / α

Diagram

RTD: Linear Approximation R = R₀(1 + αT)Temperature (°C)R (Ω)R₀ at 0 °C50 °C-1000200400R = R₀(1 + αT)

Worked example

A Pt100 RTD reads 119.25 Ω. Using α = 0.00385 1/°C, what is the temperature?

  1. 01T = (R / R₀ − 1) / α
  2. 02T = (119.25 / 100 − 1) / 0.00385
  3. 03T = (1.1925 − 1) / 0.00385
  4. 04T = 0.1925 / 0.00385
  5. 05T = 50 °C
Result

The estimated temperature is 50 °C.

FAQ

How accurate is the linear approximation?
The linear approximation R = R₀(1 + αT) is reasonably accurate for typical industrial ranges (roughly −50 °C to +200 °C). For wider ranges or high-precision work, the full Callendar–Van Dusen equation is needed, which is not implemented here.
Does this implement the full IEC 60751 standard?
No. This uses the simple linear approximation only. The full IEC 60751 Callendar–Van Dusen equation includes higher-order terms and is not implemented.
Does this include lead-wire compensation?
No. Lead-wire resistance (relevant in 2-wire and 3-wire configurations) is not compensated. For accurate measurements, use a 4-wire RTD configuration or apply external correction.
Can I use this for thermocouples?
No. Thermocouples use a different measurement principle (voltage, not resistance) and require thermocouple-specific reference tables. This calculator is for platinum RTDs only.