Thermistor / RTD Calculator THERMISTOR
Temperature ↔ resistance for the common HVAC sensors, both directions.
Inputs are seeded with an example — edit them to your numbers.
Input
Output
R / T Table
| Temperature | Resistance (Ω) |
|---|
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Measured points
Enter temperature + resistance pairs read off the unknown sensor. Three or more readings spread across a wide span give the cleanest match.
| # | Temp (°F) | Resistance (Ω) |
|---|
Best match
Every standard type, ranked by how far its published curve sits from your readings. Pick a row to open that type in Lookup.
| Sensor type | Equiv. temp error | Resistance error |
|---|
Per-point fit
| # | Measured temp | Measured Ω | Curve says | Off by |
|---|
Identify mode compares your readings against the same generated nominal curves Lookup uses — not calibration data. Sensor tolerance (±0.1 to ±1 °C is typical), meter accuracy, and self-heating all shift the numbers. Two points often cannot separate similar curves: a 10K Type II and a 10K Type III both pass through 10 kΩ at 77 °F and only diverge away from it. Spread readings across as wide a temperature span as the job allows, use three or more, and treat a close call as “one of these two” rather than a definitive ID.
About these tables
Where the values come from. Each R/T table is generated from a small set of curve parameters — β and R25 for the NTC thermistors, the parallel shunt for the linearized 10K curves, R0 and a temperature coefficient for the RTDs. The Pt100 and Pt1000 tables come from the IEC 60751 Callendar–Van Dusen polynomial (the international standard). Auditing the parameters is what makes a 500+ cell table trustworthy in one pass, instead of one row at a time.
Sources verified against (2026-05 pass). 10K Type II, 10K Type III, and 10K Type 5 (TAC) — BAPI 10K-2 / 10K-3 / 10K-3(11K) output tables, cross-checked against US Sensor "Curve G", Sontay's Compatibility Chart, and Vector Controls' multi-curve reference. 20K and 3K — Vector Controls and Sontay. 1K Balco — a Schneider EcoStruxure Building Operation resistance chart plus the ACI BALCO datasheet. Pt100 and Pt1000 — IEC 60751:2008 directly, cross-checked against Vector, Sontay, Fluke's table generator, and pt100.de. Where multiple sources disagreed, I consulted with a second tech before settling on a curve.
What's still nominal. The Johnson Controls 10K + 8.7K-shunt curve is the one type without a public R/T table — the canonical TE-6300 Product Bulletin URL redirects to a docs-portal landing page. It's modeled as a 10K Type 2 element in parallel with 8.7 kΩ, which is folklore-confirmed but datasheet-unverified. If you have a known-good JCI sensor with calibration data, that's the better reference.
Use as a reference, not for calibration. A single-β model approximates a Steinhart-Hart curve; the fit is within roughly 1 °F across 32–150 °F (the BAS operating range) and degrades to 2–5 °F of equivalent temperature error at the −40 °F extreme for the bare 10K curves. Pt100 and Pt1000 are governed by the international standard and match it exactly. For calibration-grade work, measure your sensor directly against a known-good reference at the working temperature — don't trust any published table, ours or anyone else's, blindly.