Enter the thickness of the material parallel to heat flow, the thermal conductivity, and the cross-sectional area into the calculator to determine the thermal resistance.

Thermal Resistance Formula

The following formula is used to calculate thermal resistance.

R = X / A*K 
  • Where R is the absolute thermal resistance (K/W)
  • X is the thickness of the material parallel to heat flow (m)
  • A is the cross-sectional perpendicular to heat flow (m^2)
  • K is the thermal conductivity of the material (W/(K*m))

To calculate thermal resistance, divide the thickness of material parallel to heat flow by the cross-section area perpendicular to the heat flow, then multiply by the thermal conductivity.

Thermal Resistance Definition

What is thermal resistance? Thermal resistance is a measure of the rate of change in temperature of a material per unit of energy added to the material. In other words, the resistance to the flow of heat energy.

Example Problem

How to calculate thermal resistance?

  1. First, determine the thickness of the specimen.

    For this example, the thickness of the material that is parallel to heat flow is .25m.

  2. Next, determine the cross-sectional area.

    The heat flow for this problem is moving through a square of 1m x 1m = 1m^2.

  3. Next, determine the thermal conductivity.

    This can typically be found on online tables. The material in this problem is steel which has a thermal conductivity of 45 W/(K*m).

  4. Finally, calculate the thermal resistance.

    Using the formula above, the thermal resistance is calculate as .25 / (1*45) = .0055 (K/W).

About Thermal Resistance

What does thermal resistance depend on? Thermal resistance is dependent on three factors; the thermal conductivity of the material, the thickness of the material parallel to heat flow, and the cross-sectional area perpendicular to heat flow.

Is a higher thermal resistance better? When attempting to insulate an object or structure, a higher thermal resistance is better. However, if you are looking at an application such as a frying pan, you want the thermal resistance to be as low as possible so that as much energy transfers from the burner to the food.

Can a thermal resistance be negative? Thermal resistance cannot be negative. This is because thermal conductivity, thickness, and cross-sectional area can also not be negative. Or in other words, the heat has to go somewhere.