What Is the B Value of an NTC Thermistor? How to Calculate and Choose the Right B Value

The B value is one of the most important parameters when selecting an NTC thermistor. It describes the relationship between the resistance of an NTC thermistor and temperature, and directly affects the sensor's temperature measurement accuracy and resistance-temperature characteristics.

For engineers designing temperature sensing, compensation, and control systems, understanding the B value is essential for selecting the right NTC thermistor.

In this article, we will explain what the NTC B value is, how to calculate it, and how to choose the appropriate B value for your application.

1. What Is the B Value of an NTC Thermistor?

An NTC thermistor has a negative temperature coefficient, which means its resistance decreases as temperature increases.

The B value, also called the Beta value, is a constant that characterizes the resistance-temperature relationship of an NTC thermistor.

In simple terms:

The B value indicates how rapidly the resistance of an NTC thermistor changes with temperature.

A higher B value generally means that the thermistor has a greater resistance change over the same temperature range.

The B value is usually expressed in Kelvin (K), although it is often written simply as a numerical value, such as:

• B25/50 = 3950 K
  
• B25/85 = 3435 K
  
• B25/85 = 3977 K
  
• B0/50 = 3419 K
  

The two temperatures in the B-value specification are important because the calculated B value depends on the temperature range used.

2. Why Is the B Value Important?

The B value directly influences the resistance-temperature curve of an NTC thermistor.

For example, two NTC thermistors may both have a nominal resistance of 10 kΩ at 25°C, but if their B values are different, their resistance at other temperatures will also be different.

Consider:

• NTC A: 10 kΩ, B25/85 = 3435 K
  
• NTC B: 10 kΩ, B25/85 = 3950 K
  

Although both thermistors have the same resistance at 25°C, their resistance values at 60°C, 80°C, or 100°C will differ significantly.

Therefore, selecting an NTC based only on its nominal resistance is not sufficient.

You should consider at least:

Resistance value + B value + operating temperature range + accuracy requirement

3. How to Calculate the B Value of an NTC Thermistor

The B value can be calculated from two known resistance-temperature points.

The commonly used equation is:

B = ln(R1/R2) / (1/T1 − 1/T2)

Where:

• B = B value in Kelvin (K)
  
• R1 = Resistance at temperature T1
  
• R2 = Resistance at temperature T2
  
• T1 = Temperature 1 in Kelvin
  
• T2 = Temperature 2 in Kelvin
  
• ln = Natural logarithm
  

Important: Convert Celsius to Kelvin

Before calculating the B value, temperatures must be converted from Celsius to Kelvin:

T(K) = T(°C) + 273.15

For example:

25°C = 298.15 K
85°C = 358.15 K

4. Example of B Value Calculation

Suppose an NTC thermistor has the following characteristics:

• Resistance at 25°C: 10 kΩ
  
• Resistance at 85°C: 1.37 kΩ
  

First, convert the temperatures to Kelvin:

T1 = 25 + 273.15 = 298.15 K

T2 = 85 + 273.15 = 358.15 K

Then use the formula:

B = ln(10 / 1.37) / (1/298.15 − 1/358.15)

The calculated B value is approximately 3950 K.

Therefore, this thermistor can be specified as approximately:

10 kΩ, B25/85 = 3950 K

This is a typical specification for many temperature-sensing applications.

5. What Does B25/85 Mean?

You may see specifications such as B25/50, B25/85, or B0/50 on NTC thermistor datasheets.

These numbers indicate the two reference temperatures used to determine the B value.

For example:

B25/85

The B value is calculated using resistance measurements at:

• 25°C
  
• 85°C
  

B25/50

The B value is calculated using:

• 25°C
  
• 50°C
  

B0/50

The B value is calculated using:

• 0°C
  
• 50°C
  

Because different temperature ranges are used, the B value numbers may not be directly interchangeable.

Always check the B-value definition and reference temperatures when comparing different NTC thermistors.

6. How Does the B Value Affect NTC Resistance?

The resistance-temperature relationship of an NTC thermistor can be approximated using the Beta equation:

R(T) = R0 × exp[B(1/T − 1/T0)]

Where:

• R(T) = Resistance at temperature T
  
• R0 = Resistance at reference temperature T0
  
• B = B value
  
• T = Target temperature in Kelvin
  
• T0 = Reference temperature in Kelvin
  
• exp = Exponential function
  

The most common reference temperature is 25°C, so you will often see NTC thermistors specified as:

R25 = 10 kΩ

This means the thermistor's nominal resistance is 10 kΩ at 25°C.

The B value then determines how the resistance changes as temperature moves away from 25°C.

7. How to Choose the Right B Value

Choosing the right B value depends mainly on the operating temperature range and required measurement accuracy.

① Determine the Operating Temperature Range

First, identify the actual temperature range in which the NTC will operate.

For example:

• 0–50°C
  
• -20–80°C
  
• -40–125°C
  
• 0–150°C
  

An NTC designed for a narrow temperature range may not provide the best accuracy over a wider range.

② Determine the Required Accuracy

If the application requires high temperature measurement accuracy, simply selecting a standard B value may not be sufficient.

You should consider:

• B-value tolerance
  
• Resistance tolerance
  
• Temperature accuracy
  
• Resistance-temperature curve
  
• Long-term stability
  

For precision applications, a customized R-T curve may provide better performance than a standard thermistor.

③ Select the Appropriate Reference Resistance

The nominal resistance is also important.

Common NTC resistance values include:

• 1 kΩ
  
• 2.2 kΩ
  
• 5 kΩ
  
• 10 kΩ
  
• 15 kΩ
  
• 20 kΩ
  
• 50 kΩ
  
• 100 kΩ
  

For many HVAC and household appliance applications, 10 kΩ NTC thermistors are widely used.

However, the optimal resistance depends on the circuit design, ADC range, pull-up resistor, operating temperature, and required resolution.

④ Match the B Value to the Application

Different applications may require different B values.

For example:

HVAC and air conditioning:
Common specifications include 5 kΩ, 10 kΩ, 15 kΩ, and different B values depending on the controller and temperature range.

Household appliances:
Coffee machines, refrigerators, dishwashers, water heaters, and other appliances may require customized resistance and B-value characteristics.

Battery and BMS applications:
The NTC needs to provide stable and accurate temperature detection across the battery's operating temperature range.

Industrial temperature sensing:
A customized R-T curve and tighter tolerance may be required for higher accuracy.

8. B Value Is Not the Only Parameter to Consider

Although the B value is important, it should not be considered independently.

When selecting an NTC thermistor, engineers should also evaluate:

Therefore, the best NTC thermistor is not necessarily the one with the highest or lowest B value, but the one whose complete electrical and mechanical characteristics match the application.

9. B Value vs. Temperature Accuracy

One common misunderstanding is that a higher B value automatically means better accuracy.

This is not necessarily true.

The B value describes the slope of the resistance-temperature relationship, but actual temperature accuracy is also affected by:

• Resistance tolerance
  
• B-value tolerance
  
• R-T curve accuracy
  
• Calibration
  
• Circuit design
  
• ADC resolution
  
• Self-heating
  
• Thermal contact
  
• Sensor construction
  

For demanding applications, manufacturers can provide customized R-T characteristics and tighter resistance/B-value tolerances to meet specific accuracy requirements.

10. Standard B Value or Customized B Value?

A standard NTC thermistor may be sufficient for general-purpose applications.

However, customized NTC thermistors are often a better solution when the application requires:

• Higher temperature accuracy
  
• A specific R-T curve
  
• A special operating temperature range
  
• Faster response time
  
• Special dimensions
  
• Waterproof construction
  
• Customized wire or connector
  
• Special probe housing
  
• High-temperature resistance
  
• Long-term stability
  

For example, instead of simply specifying:

10 kΩ, B = 3950 K

an engineering team may specify a complete R-T curve with resistance limits at multiple temperature points.

This allows the NTC thermistor to be matched more precisely to the customer's electronic control system.

11. Common NTC B Values

There is no single standard B value for all NTC thermistors.

Common specifications may include:

• B25/50 = 3950 K
  
• B25/85 = 3435 K
  
• B25/85 = 3977 K
  
• B0/50 = 3419 K
  

The correct B value depends on the thermistor material, manufacturing process, and application requirements.

When replacing an existing NTC thermistor, it is important to match both the resistance value and the B-value specification.

12. How Xinshiheng Helps You Choose the Right NTC Thermistor

As an experienced NTC thermistor and temperature sensor manufacturer, Xinshiheng provides standard and customized NTC solutions for different applications.

We can support customers with:

• Customized resistance values
  
• Customized B values
  
• R-T curve matching
  
• Tight resistance tolerance
  
• Tight B-value tolerance
  
• Different operating temperature ranges
  
• Customized probe structures
  
• Wire and connector customization
  
• Fast-response NTC sensors
  
• Epoxy-coated and glass-sealed NTC thermistors
  
• Customized temperature sensor assemblies
  

If you already have an existing thermistor sample, drawing, R-T curve, or technical specification, our engineering team can evaluate the requirements and recommend a suitable solution.