Thermistor Beta Calculator

You need an external temperature measurement device. Any of these work:

— K-type thermocouple probe — most accurate for this task. A multimeter with thermocouple input works great. Position the tip as close to the heater block as possible, or use thermal paste for better contact.
— IR thermometer — convenient but less accurate on shiny metal surfaces; matte surfaces give better readings.
— Thermal camera — works well and lets you see the temperature distribution across the whole hotend area at once.

Heat your hotend (or bed) to 3 different temperatures using your normal Klipper interface. Wait at least 2–3 minutes after it stabilizes before reading the external thermometer.

Recommended temperature points for a hotend:

You need the beta value that Klipper is using at each of those temperatures. You can find these in the Klipper source or documentation for your thermistor type.

Common starting values for Generic 3950 thermistors:

Enter the actual temperature you measured externally (not the Klipper target) in the "Actual Temp" field. Enter the corresponding beta for that reference temperature. Then set your target print temperature and click Calculate.

For the most accurate calibration, you should also measure the actual resistance of your thermistor at a known ambient temperature — rather than relying on the datasheet nominal value (usually 100kΩ at 25°C), which can vary between individual sensors.

To do this: disconnect the thermistor from the board, let it sit at room temperature until it stabilises, then measure its resistance with a multimeter. At the same time, note the ambient temperature using your external thermometer. These two values go directly into temperature1 and resistance1 in the config.

Define a custom thermistor in Klipper and reference it in [extruder]. This keeps all your calibration data in one place and doesn't touch the built-in sensor definitions.

Run FIRMWARE_RESTART in the Klipper console, then verify with your external thermometer at a couple of temperatures that the readings now match. Small residual errors (<2°C) are normal.