10K NTC Temperature Sensor Thermistor Waterproof Probe - 1m

A 10K NTC temperature sensor: a waterproof thermistor probe with a sealed stainless steel tip on a 1 metre lead. It's a simple, low-cost way to measure temperature in liquids, soil, enclosures and fridges with any microcontroller that has an analog input, including the Arduino Uno and ESP32.

NTC stands for Negative Temperature Coefficient: the resistance drops as the temperature rises. At 25°C it reads 10kΩ (±1%), and with a B value of 3950 you can convert any resistance reading into a temperature with a single formula.

Specifications

• Sensor type: NTC thermistor, 2-wire
• Resistance at 25°C: 10kΩ ±1%
• B value (Beta): 3950
• Operating range: -20°C to +105°C
• Dissipation constant: 5mW/°C (typical)
• Insulation resistance: >100MΩ
• Dielectric strength: AC 1800V, 1mA for 2 seconds
• Lead tensile strength: 9.8N (1kgf) for 1 minute
• Probe size: 4mm diameter x 20mm
• Probe material: Stainless steel, sealed tip
• Lead length: 1m

How to Wire It

A thermistor is a variable resistor, not a digital sensor, so it can't connect straight to a pin. Wire it as a voltage divider with a fixed 10kΩ resistor:

• One thermistor lead to GND
• Other thermistor lead to your analog input (e.g. A0)
• A 10kΩ resistor from that same analog input to VCC (5V on an Uno, 3.3V on an ESP32)

The thermistor leads are not polarised, so either wire can go to either side. If you don't have a 10kΩ resistor on hand, our 1% metal film resistor packs or the 600pc resistor kit include them. Use a 1% resistor so it doesn't add more error than the thermistor itself.

Converting the Reading to Temperature

First calculate the thermistor's resistance from the ADC value, then apply the Beta equation:

• R = 10000 x ADC / (ADC_max - ADC), where ADC_max is 1023 on an Uno or 4095 on an ESP32
• 1/T = 1/298.15 + (1/3950) x ln(R / 10000), giving T in Kelvin (subtract 273.15 for °C)

The Beta equation is most accurate around 0 to 50°C. For better accuracy across the full range, use the Steinhart-Hart equation or calibrate against a known reference such as ice water (0°C).

Accuracy Notes

• Near 25°C: the ±1% resistance tolerance works out to roughly ±0.25°C. Accuracy drops further away from 25°C.
• Self-heating: current through the thermistor warms it slightly. A 10kΩ divider keeps this negligible; avoid lower value resistors.
• ESP32 users: the ESP32 ADC is non-linear near 0V and 3.3V, so readings at the extremes of the range will be less precise. Use an ADC1 pin (GPIO 32 to 39), as ADC2 pins can't be read while Wi-Fi is active.

Applications

• Aquarium and pond water temperature
• Homebrewing, fermentation and sous vide monitoring
• Fridge, freezer and cool room monitoring (down to -20°C)
• Soil and greenhouse temperature
• Battery pack, enclosure and heatsink temperature

The sealed stainless tip can be immersed in liquid. Keep the point where the cable meets the probe out of water for long-term installations, and stay under the 105°C limit, which rules out uses like 3D printer hotends.

NTC Thermistor or DS18B20?

This thermistor is analog: cheap, fast to respond and easy to wire, but it needs a calibration formula and one analog pin per sensor. If you'd rather get a calibrated digital reading in °C, or want to run several probes on a single pin, the DS18B20 waterproof probe is the better choice. Our guide DHT11 vs DHT22 vs BME280 vs DS18B20 compares the digital options in detail.

What's Included

• 1x 10K NTC thermistor waterproof probe with 1m lead