TIMs are typically characterized by the thermal conductivity in terms of Watts per Meters-Celsius (W/(m °C)) or Watts per Meters-Kelvin (W/(m K)). Celsius and Kelvin are interchangeable in this example because they both use the same increment of temperature measurement and it is the rise/fall of temperature that is being calculated. For example, a 45°C rise in temperature is equivalent to a 45°K rise in temperature. The unit of meters is present because the impedance of the TIM is dependent upon the ratio of thickness (the thickness of the TIM in terms of meters) over area (the area which the TIM is spread over in terms of meters²), which results in 1/m (calculated as m/m² = 1/m). In this example, a thin layer of TIM will be applied over the metal tab area of a TO-220 case. When taking into account the TIM’s thermal conductivity, area of application, and thickness of application, the thermal impedance of the TIM in this example is calculated to be 0.45°C/W or 0.45°K/W.