The temperature coefficient of resistance (TCR) is a measure of the change in electrical resistance of a material with respect to a change in temperature. It is usually expressed in units of parts per million per degree Celsius (ppm/°C) or parts per million per degree Kelvin (ppm/K) . The TCR is calculated as the average slope of the resistance value over a temperature range. A positive TCR means that the resistance of a material increases with an increase in temperature, while a negative TCR means that the resistance decreases with an increase in temperature. The TCR is determined by measuring the resistance values over an appropriate temperature range. The following factors determine the change in electrical resistance of a substance due to temperature:

• The value of resistance at an initial temperature.
• The rise in temperature.
• The temperature coefficient of resistance α.

The TCR is an important parameter that characterizes the performance of a resistor. It is used to calculate the resistance change factor per degree of temperature change. The TCR is also used to estimate the value of resistance at a temperature T, given its value at a reference temperature T0. The temperature dependence of electrical resistance and thus of electronic devices (wires, resistors) has to be taken into account when constructing devices and circuits. The temperature dependence of conductors is to a great degree linear and can be described by the approximation below:

$$R_T = R_0(1 + \alpha T)$$

where R_T is the resistance at temperature T, R_0 is the resistance at a reference temperature, α is the specific resistance temperature coefficient at a specified reference value (normally T = 0 °C), and T is the temperature in Celsius. The temperature dependence of semiconductors and insulators is exponential.