Calculator KB-37
NTC thermistor calculator
The cheapest temperature sensor, found in chargers, 3D printers, and power supplies.
Result
In brief: NTC thermistor calculator using the beta parameter: resistance at a given temperature, temperature from measured resistance, temperature coefficient, and voltage divider output. Example: Unknown value: 697.5 Ω.
Calculation example
| R25 | 10000 Ω |
|---|---|
| B coefficient | 3950 K |
| Known values | Temperature |
| Temperature | 100 °C |
| Divider resistor | 10000 Ω |
| Divider supply voltage | 3.3 V |
| Unknown value | 697.5 Ω |
|---|---|
| Resistance | 697.5 Ω |
| Temperature | 100 °C |
| Change per degree | -2.84 %/°C |
| Voltage across thermistor | 215.2 mV |
How it is calculated
T in kelvins
NTC resistance drops rapidly and nonlinearly as temperature rises. The formula using the B parameter is accurate enough over a range of about 25–100 °C. For a wider range, use the Steinhart–Hart equation or the table in the datasheet.
What to look for
- The measurement current heats the thermistor. Keep it low, usually below 100 µA for accurate measurements.
- The divider resistor is usually chosen to match the thermistor's resistance at the midpoint of the operating range.
Frequently asked questions
What is the resistance of a 10 kΩ NTC at 100 °C?
About 697 Ω for B = 3950: R = R₂₅ · e^(B · (1/T − 1/298.15)), where T is in kelvins.
How do I convert thermistor resistance to temperature?
T = 1 / (1/298.15 + ln(R / R₂₅) / B) − 273.15. For 4.7 kΩ, a 10 kΩ thermistor with B = 3950 gives about 43 °C.
What resistor should I use in a divider with an NTC?
Choose one roughly equal to the thermistor's resistance at the midpoint of its operating range: that's where sensitivity is highest. For room temperatures, pair a 10 kΩ thermistor with a 10 kΩ resistor.
