A 50k ohm thermistor is a Negative Temperature Coefficient (NTC) sensor with a nominal resistance of 50,000 Ω at 25°C (77°F). Because NTC thermistors are highly non-linear, you cannot simply calculate temperature using Ohm's law; you must rely on a lookup table or the Steinhart-Hart equation. This 50k ohm thermistor chart provides the exact resistance values for the two most common Beta (β) variants used in HVAC, 3D printer hotends, and battery management systems (BMS).
How to Read This 50k Ohm Thermistor Chart
Before taking a measurement, you need to know which column applies to your specific installation. The resistance-to-temperature curve is dictated by the thermistor's Beta (β) parameter, which represents the material constant of the semiconductor ceramic.
- Beta 3950 Column: This is the industry standard for 3D printer extruders, heated beds, and many DIY Arduino/ESP32 temperature projects. It offers a steeper resistance drop at higher temperatures, providing better ADC resolution in the 150°C–250°C range.
- Beta 3435 Column: Frequently found in automotive coolant sensors, lithium-ion BMS temperature probes, and commercial HVAC systems. It provides a slightly more linear curve in the -20°C to +80°C range.
- Power Derating Factor Column: This column tells you how to adjust the maximum allowable excitation current to prevent self-heating errors as ambient temperature rises.
The values below are calculated using the standard Beta parameter equation derived from Murata's NTC specification standards and align with the testing parameters outlined in MIL-PRF-23648 for discrete NTC thermistors.
50k NTC Thermistor Resistance vs. Temperature Table
Use the bookmark-friendly anchor IDs (e.g., 0°C, 25°C, 100°C) to jump to the most queried baseline values. Tolerance bands (typically ±1% to ±5%) are not included in the raw numbers below; apply your manufacturer's tolerance multiplier to these baseline figures for your error margins.
| Temp (°C) | Temp (°F) | Beta 3950 (Ω) | Beta 3435 (Ω) | Power Derating Factor |
|---|---|---|---|---|
| -40 | -40 | 2,145,000 | 1,480,000 | 1.00 |
| -20 | -4 | 526,000 | 387,000 | 1.00 |
| 0 | 32 | 168,000 | 143,500 | 1.00 |
| 10 | 50 | 98,500 | 89,200 | 0.95 |
| 25 | 77 | 50,000 | 50,000 | 0.85 |
| 40 | 104 | 28,400 | 30,100 | 0.75 |
| 60 | 140 | 13,200 | 15,400 | 0.65 |
| 80 | 176 | 6,300 | 8,300 | 0.50 |
| 100 | 212 | 3,480 | 4,900 | 0.35 |
| 125 | 257 | 1,450 | 2,250 | 0.00 |
Derating, Tolerances, and What the Table Cannot Tell You
A common mistake on the bench is assuming a thermistor's resistance is purely a function of ambient temperature. In reality, the current you push through the sensor to measure it generates heat (I²R losses). This is where the Power Derating Factor column becomes critical.
How Derating Rows Modify the Base Value
Most standard glass-encapsulated 50k NTC thermistors have a base maximum power dissipation rating of 5mW at 25°C. If you exceed this, the thermistor heats itself, causing a false low-resistance (high-temperature) reading. As the ambient environment gets hotter, the thermistor's ability to shed that self-generated heat drops.
To calculate your maximum allowable excitation power at a given temperature, multiply the base power rating by the derating factor. For example, at 80°C, the derating factor is 0.50. Your new max power limit is 5mW × 0.50 = 2.5mW. If your microcontroller's voltage divider is pushing 3mW through the sensor at 80°C, your readings will drift due to self-heating. Always use high-value pull-up resistors (e.g., 50kΩ to 100kΩ) and sample the ADC briefly to minimize excitation time.
What This Table Cannot Tell You
While this 50k ohm thermistor chart gives you the steady-state resistance, it omits three critical dynamic specifications found in TI's thermistor application notes:
- Thermal Time Constant (τ): The time it takes for the sensor to reach 63.2% of a new temperature. A glass bead in still air might take 15 seconds, while the same bead in liquid coolant takes 2 seconds.
- Dissipation Constant (δ): Measured in mW/°C, this tells you exactly how much power is required to raise the sensor's internal temperature by 1°C above ambient.
- Long-Term Drift: Standard NTCs drift by 0.1% to 0.5% per year at elevated temperatures. If you are building a precision BMS, you must recalibrate or replace 50k probes every 2-3 years if they constantly operate above 80°C.
50k Thermistor FAQ
Can I use a 50k Beta 3950 thermistor in place of a 50k Beta 3435?
No. While both will read exactly 50,000 Ω at 25°C, their resistance curves diverge aggressively outside of room temperature. At 100°C, the Beta 3950 reads 3,480 Ω, while the Beta 3435 reads 4,900 Ω. If you swap them without updating the Steinhart-Hart coefficients or Beta lookup table in your firmware, your microcontroller will read 100°C as roughly 82°C, which can lead to catastrophic thermal runaway in 3D printers or battery packs.
Why does my multimeter read 48.2k ohms on a brand new 50k thermistor?
Two factors are at play. First, standard 50k thermistors have a manufacturing tolerance of ±1% to ±5%. A ±2% tolerance means the sensor could legally read anywhere from 49k to 51k Ω at exactly 25.0°C. Second, your room temperature is likely not exactly 25.0°C. If your bench is 27°C, a Beta 3950 thermistor will naturally drop to roughly 48.1k Ω. To verify a dead-on-arrival sensor, submerge it in an ice-water bath (0°C) and check if it reads near 168k Ω (for β3950).
How do I wire a 50k NTC thermistor to an Arduino or ESP32 ADC?
Wire the thermistor as the lower half of a voltage divider. Connect one leg to GND, and the other leg to a 3.3V or 5V rail through a 50kΩ precision (1% or better) pull-up resistor. Tap the junction between the resistor and the thermistor to your ADC pin. For ESP32 boards, avoid the high-numbered ADC2 pins if you are using WiFi, as ADC2 is disabled during radio transmission. Use ADC1 pins (e.g., GPIO34, GPIO35) and call analogReadMilliVolts() rather than raw analogRead() to bypass the ESP32's notorious internal ADC non-linearity.
Does lead wire resistance affect 50k thermistor accuracy?
Practically, no. Unlike PT100 RTDs where 1 Ω of copper lead wire causes a 2.5°C error, a 50k NTC thermistor operates at such high base impedances that standard wire resistance is negligible. Adding 3 feet of 22 AWG copper wire introduces roughly 0.05 Ω of series resistance. Against a 50,000 Ω baseline, that is a 0.0001% error, translating to a temperature deviation of less than 0.01°C. You can safely use long, thin extension wires for 50k thermistors without needing 3-wire or 4-wire Kelvin compensation circuits.
Where can I find the exact Steinhart-Hart coefficients for my specific sensor?
The Beta equation used to generate the chart above is an approximation that loses accuracy at temperature extremes. For precision applications, you need the Steinhart-Hart coefficients (A, B, and C). These are rarely printed on the component itself. You must request the specific datasheet from the manufacturer (e.g., Vishay, Murata, Semitec) using the exact part number printed on the packaging. If the part number is lost, you can calculate the coefficients yourself by measuring the resistance at three known temperatures (e.g., ice bath, boiling water, and room temp) and solving the system of equations.
