RTD / PT100 / PT1000 Calculator
Convert PT100 and PT1000 temperature points into resistance and measured resistance back into corrected temperature. The tool uses IEC 60751 curve math, applies Class AA / A / B tolerance logic, models 2-wire / 3-wire / 4-wire behavior, and generates calibration tables you can move straight into commissioning and troubleshooting workflows.
Sensor Setup
Sensor family
100 ohm platinum RTD at 0 degC. Common in industrial transmitters, PLC cards, and field indicators.
IEC accuracy class
+/- (0.15 + 0.002 x |t|) degC. Common industrial accuracy class that balances practical cost and temperature uncertainty.
Wire mode
3-wire assumes matched leads and a properly compensated analog input or transmitter.
Temperature unit
Input fields follow this unit. The generated table always includes both degC and degF columns.
Use the estimated resistance of one lead conductor. Two-wire adds both conductors into the measured loop.
Nominal R0
100 ohm
At 0 degC with IEC alpha 0.00385 ohm/ohm/degC.
Resistance range
18.5201 ohm to 390.4811 ohm
Corresponds to -200 to 850 degC for the chosen sensor family.
Solve
Use this mode to generate a PT100/PT1000 resistance target for calibration or transmitter checkout.
How this model behaves
It uses the IEC 60751 Callendar-Van Dusen curve for PT100 and PT1000, then applies class tolerance and idealized wire-mode correction. That turns the page into a calibration and troubleshooting aid instead of a single-point formula box.
Current setup reminder
PT100, Class A, 3-wire, lead 0.25 ohm per conductor.
Result
Summary
Enter a temperature in degC to calculate the RTD resistance and tolerance band.
This result assumes IEC 60751 curve behavior and ideal wire-mode handling for 3-wire and 4-wire measurement.
Corrected temperature
Waiting for temperature
This is the sensor temperature after the selected wire-mode correction is applied.
Sensor element resistance
Enter a value
Pure RTD element resistance without added lead-wire contribution.
Receiver sees
Enter a value
Equivalent resistance at the instrument input or field measurement point.
Class A tolerance
Select a class
Tolerance band is calculated at the corrected sensor temperature.
Calibration Table Generator
Quick presets
Preset buttons load common RTD commissioning and reference-table ranges.
| Temp degC | Temp degF | Sensor ohm | Tolerance degC | Low ohm | High ohm |
|---|---|---|---|---|---|
| -50 | -58 | 80.306282 | 0.25 | 80.206996 | 80.405559 |
| -40 | -40 | 84.270652 | 0.23 | 84.179624 | 84.361673 |
| -30 | -22 | 88.221657 | 0.21 | 88.138819 | 88.304489 |
| -20 | -4 | 92.159898 | 0.19 | 92.085188 | 92.234605 |
| -10 | 14 | 96.085879 | 0.17 | 96.019237 | 96.152517 |
| 0 | 32 | 100 | 0.15 | 99.941374 | 100.058623 |
| 10 | 50 | 103.902525 | 0.17 | 103.836279 | 103.968768 |
| 20 | 68 | 107.7935 | 0.19 | 107.719679 | 107.867317 |
| 30 | 86 | 111.672925 | 0.21 | 111.591576 | 111.754269 |
| 40 | 104 | 115.5408 | 0.23 | 115.451969 | 115.629625 |
| 50 | 122 | 119.397125 | 0.25 | 119.300858 | 119.493385 |
| 60 | 140 | 123.2419 | 0.27 | 123.138243 | 123.345549 |
| 70 | 158 | 127.075125 | 0.29 | 126.964124 | 127.186116 |
| 80 | 176 | 130.8968 | 0.31 | 130.778502 | 131.015087 |
| 90 | 194 | 134.706925 | 0.33 | 134.581375 | 134.832462 |
| 100 | 212 | 138.5055 | 0.35 | 138.372745 | 138.638241 |
| 110 | 230 | 142.292525 | 0.37 | 142.152611 | 142.432423 |
| 120 | 248 | 146.068 | 0.39 | 145.920973 | 146.21501 |
| 130 | 266 | 149.831925 | 0.41 | 149.677831 | 149.985999 |
| 140 | 284 | 153.5843 | 0.43 | 153.423186 | 153.745393 |
| 150 | 302 | 157.325125 | 0.45 | 157.157036 | 157.493191 |
CSV export
Copy the generated table into a calibration sheet, FAT checklist, or commissioning note.
Assumptions & Usage Notes
This tool assumes IEC 60751 alpha 0.00385 platinum sensors and an idealized lead-wire model. Three-wire mode assumes matched leads with proper compensation, and four-wire mode assumes Kelvin measurement. It does not model transmitter-specific burnout, sensor self-heating, or analog-input filter behavior.
IEC 60751 Curve Reference
| Topic | Expression | Meaning |
|---|---|---|
| Resistance above 0 degC | R(t) = R0 x (1 + A x t + B x t^2) | IEC 60751 Callendar-Van Dusen relationship used for the positive-temperature PT100/PT1000 curve. |
| Resistance below 0 degC | R(t) = R0 x (1 + A x t + B x t^2 + C x (t - 100) x t^3) | Adds the low-temperature correction term needed to model the curve below freezing. |
| Class AA tolerance | +/- (0.1 + 0.0017 x |t|) degC | Use when the measurement chain needs tighter acceptance limits or calibration-grade checkpoints. |
| Class A / B tolerance | Class A: +/- (0.15 + 0.002 x |t|) degC, Class B: +/- (0.3 + 0.005 x |t|) degC | Useful for comparing practical RTD element classes before field calibration or transmitter setup. |
Engineering Workflow Matrix
| Scenario | Objective | Recommendation | Critical Checks |
|---|---|---|---|
| Bench calibration | Confirm the expected PT100 or PT1000 ohms at a target temperature point | Start with temperature to resistance mode, then generate a narrow table around the expected checkpoints for the bath or dry block. | Selected nominal sensor, class tolerance, 2-wire versus 3-wire setup, transmitter trim assumptions |
| Field troubleshooting | Explain why a panel input reads hotter than the actual process | Use resistance to temperature mode with 2-wire lead resistance enabled to separate sensor resistance from cable contribution. | Lead resistance per conductor, terminal quality, wire gauge, extension length, actual sensor nominal |
| Transmitter setup | Build a commissioning sheet for RTD input or transmitter trim | Generate a table with low, mid, and high checkpoints plus the class-based low and high resistance acceptance band. | Input type setting, input linearization standard, span points, class AA/A/B acceptance window |
| Choosing PT100 vs PT1000 | See how nominal resistance affects sensitivity to wiring error | Compare the same wire resistance and temperature range with both sensor families. PT1000 reduces the error impact of the same lead ohms. | Lead-length budget, noise floor, transmitter compatibility, installed sensor standard |
Worked Example
A PT100 at 100 degC should be about 138.5055 ohm. If the loop is wired as a 2-wire circuit and each lead adds 0.8 ohm, the receiver sees about 140.1055 ohm.
If the receiver interprets that full value as pure sensor resistance, the apparent temperature rises several degrees above the real process temperature. In this example the card would read about 104.22 degC even though the sensor element itself is still exactly on target at 100 degC.
That is why this tool separates sensor resistance, receiver resistance, and corrected temperature instead of giving you only one number.
Why This Tool Matters
RTD problems often hide in places that a simple resistance table does not reveal: the wrong nominal sensor, a two-wire install with too much lead resistance, or a tolerance class that was never considered during acceptance testing.
The practical job is rarely just converting one point. It is proving that the sensor, wiring, transmitter, and acceptance window all agree before the value goes into a PLC, historian, or control loop.
That is why the page combines inverse conversion, class tolerance, wire-mode correction, and table generation in one workflow.
Frequently Asked Questions
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