Heat sink size calculations can be daunting tasks for any one who does not have much experience in thermal analysis. There are commercially available heat sink design software that would allow you to design and analyze a heat sink to meet the thermal requirements of the device(s) to be cooled. If that type of software is not available to you some quick calculations using a spreadsheet or mathematical software can be done to get an estimate of the heat sink size required to maintain the desired temperature of your components.
Heat sink design assumptions
By making a few simplifying assumptions you can conduct the heat sink analysis by hand or using a spreadsheet. The output of these calculations will be the dimensions of the heat sink required to maintain the required source temperature.
Figure 1. Plate fin heat sink dimensions
Figure 1 shows a typical plate fin heat sink used to cool common electrical / electronic components such as LEDs used in lighting applications and MOSFET used in digital circuits and microprocessors. There are six dimensions that would need to be determined to design an appropriate heat sink for your needs. In order to reduce the complexity of the calculations the following assumptions will be made: