How to use it
- Choose the Sensor, Pt100 or Pt1000, from the list.
- Type the Temperature, °C, for example 100.
- Read the Resistance, Ω, then the table of standard temperatures and the steps.
The Callendar-Van Dusen equation
The resistance of a platinum resistance thermometer rises with temperature along a smooth curve, which the Callendar-Van Dusen equation describes. IEC 60751 gives the coefficients for the common industrial sensors, and the equation below is the form that the standard uses.
R(t) = R0 × [1 + A × t + B × t² + C × (t − 100) × t³]
R0 = resistance at 0 °C, Ω (100 for Pt100, 1000 for Pt1000)
t = temperature, °C
A = 3.9083 × 10⁻³ /°C
B = −5.775 × 10⁻⁷ /°C²
C = −4.183 × 10⁻¹² /°C⁴ below 0 °C; 0 from 0 °C upwards- The C term is used only below 0 °C. Above 0 °C the equation has three terms.
- A Pt1000 has the same factor as a Pt100, multiplied by ten, because the equation scales with R0.
- The coefficients are those of the PT-385 curve, the most common platinum sensor curve.
Standard temperatures
The table gives the Pt100 resistance at some standard temperatures, from the same equation. The tool prints the same table for the sensor you choose.
| Temperature, °C | Pt100, Ω |
|---|---|
| -200 | 18.520 |
| -100 | 60.256 |
| 0 | 100.000 |
| 200 | 175.856 |
| 400 | 247.092 |
What the calculator does not include
- Temperatures outside −200 °C to 540 °C, where the coefficients of this table do not apply.
- Lead-wire resistance and the wiring of the sensor, with two, three or four wires.
- The calibration of one particular sensor. The equation with the standard coefficients describes the standard curve; a calibration certificate gives the values of a given sensor.
Worked example: a Pt100 at 100 °C
The factor is 1 + A × t + B × t² = 1 + 0.39083 − 0.005775 = 1.385055, so the resistance is R = 100 × 1.385055 = 138.5055 Ω. Below 0 °C the C term is added: at −200 °C the three terms and the C term give 1 − 0.78166 − 0.0231 − 0.0100392 = 0.1852008, so the resistance is 18.5201 Ω.
| Temperature, °C | Pt100 resistance, Ω |
|---|---|
| -200 | 18.520 |
| -100 | 60.256 |
| 0 | 100.000 |
| 200 | 175.856 |
| 400 | 247.092 |
Frequently asked questions
Why does a Pt1000 read ten times the Pt100 value?
Its resistance at 0 °C is 1000 Ω instead of 100 Ω, and the equation scales with that value, so every reading is ten times as large at the same temperature.
Why is the C term used only below 0 °C?
The standard's equation has a fourth term for negative temperatures. The source sets it to zero from 0 °C upwards, so the curve above zero has only three terms.
Does the calculator include the lead wires?
No. It gives the resistance of the sensor element. Long lead wires add their own resistance, which a three-wire or four-wire connection is designed to cancel.
Can I use the result to calibrate my own sensor?
No. The equation with the standard coefficients describes the standard curve. A calibrated sensor has its own values on its certificate, and those should be used for it.
Is my data sent to a server?
No. The calculation runs in your browser, and nothing you type is sent to us or stored.
Sources
- Fluke, PT100 calculator: coefficients A, B and C of the PT-385 curve, from IEC 60751:2008
- Wikipedia, Callendar–Van Dusen equation (the equation form, and the standard DIN/IEC 60751)
Figures and text last checked on Wednesday, November 11, 2026.