RTD Resistance To Temperature Calculator

Work out rtd resistance to temperature instantly with clear inputs, formula shown and shareable results.

About RTD Resistance To Temperature Calculator

The Callendar-Van Dusen equation R = R0(1 + At + Bt squared) inverts to a quadratic for temperature above 0 degrees C. A Pt100 changes only 0.385 ohm per degree, so one ohm of lead resistance is a 2.6 degree error — which is why three- and four-wire connections exist.

Formula

Callendar-Van Dusen

R = R0 (1 + A t + B t^2), A = 3.9083e-3, B = -5.775e-7 for a 385 ppm platinum RTD

Worked example

With the default values below, RTD Resistance To Temperature Calculator returns Temperature of 50.01. Change any input above and every figure here is recalculated in your browser.

Inputs used

Measured resistance: 119.4 Ω
Resistance at 0 degrees C: 100 Ω
Temperature coefficient: 0.00385 /°C

Results

Temperature: 50.01 °C
Linear approximation: 50.39 °C
Sensitivity at this point: 0.3850 Ω/°C
Error from 1 ohm of lead resistance: 2.60 °C

Step by step

1Values used
2Callendar-Van Dusen
3Temperature= 50.01 °C
4Linear approximation= 50.39 °C
5Sensitivity at this point= 0.3850 Ω/°C
6Error from 1 ohm of lead resistance= 2.60 °C

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why use three or four wires?

To cancel lead resistance. Two-wire connection adds the cable resistance directly to the measurement, which at 0.385 ohm per degree is a large error.

Pt100 or Pt1000?

Pt1000 has ten times the sensitivity, so lead and noise errors matter ten times less. It is the better choice unless legacy instrumentation dictates Pt100.