Converts between temperature and resistance of a Pt100 or Pt1000 platinum RTD — practically from a table or exactly with the IEC 60751 model. For service, commissioning or checking a measuring input. Free, no sign-up; the calculation runs only in your browser.
The number of decimals shown is not the accuracy of a measurement.
Related tools: 4–20 mA calculator → · Flow calculator → · Thermocouple K / J → · All tools →
The calculator checks the conversion. If the measurement still doesn't match, the cause is often the sensor, wiring, leads, input or transmitter settings — that is instrumentation, commissioning and troubleshooting work.
A Pt100 has 100 Ω at 0 °C, a Pt1000 has 1000 Ω. Both are platinum resistance thermometers (RTDs) with the standard IEC 60751 characteristic — the same curve, differing only in the nominal value R0.
Rounded examples: Pt100 — 0 °C = 100 Ω, 100 °C ≈ 138.5 Ω; Pt1000 — 0 °C = 1000 Ω, 100 °C ≈ 1385 Ω.
The higher resistance of a Pt1000 means the same lead resistance is a relatively smaller part of the measured value. It does not automatically remove lead-wire error.
The exact mode uses the equations of the standard with the standard coefficients:
T ≥ 0 °C: R(T) = R0 · (1 + A·T + B·T²) T < 0 °C: R(T) = 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
Resistance to temperature is solved analytically above 0 °C and numerically below 0 °C (Newton's method safeguarded by bisection, bounded number of iterations).
The practical mode uses a table generated from the IEC 60751 model in 10 °C steps and interpolates linearly between points — much like working with a table in the field. Its difference from the IEC model is at most about 0.01 °C over the whole range (largest near −200 °C).
That is the difference between two calculations, not the accuracy of a measurement.
Lead resistance affects an RTD measurement differently depending on the connection:
This tool does not calculate lead-wire compensation.
The RTD calculation is only one part of the measuring chain. Real deviation can come from:
The calculation uses the characteristic of a standard platinum RTD per IEC 60751. The result does not replace calibration, a tolerance analysis, lead-wire compensation, a check of the measuring input or an uncertainty assessment of the whole measuring chain.
The practical mode is an indicative service aid. The IEC mode is a mathematical model of the sensor characteristic. Neither says anything by itself about the real accuracy of a specific sensor in operation.