The ATX form factor is the most common and widely used motherboard size. ATX motherboards offer ample expansion slots, including multiple PCIe slots for graphics cards and other expansion cards.

ATX motherboards are generally larger and require compatible mid-tower or full-tower computer cases.

microATX motherboards are smaller than ATX but still offer a fair amount of expansion options, including PCIe slots and RAM slots. They are suitable for smaller form factor builds or users who don't need extensive expansion capabilities.

microATX motherboards are compatible with both microATX and ATX computer cases.

mini-ITX motherboards are the smallest mainstream form factor. While they have limited expansion options, they are ideal for compact and minimalist builds. mini-ITX motherboards typically have a single PCIe slot and two RAM slots.

Due to their size, mini-ITX motherboards require compatible mini-ITX computer cases.

E-ATX motherboards are larger than standard ATX and offer additional expansion options. They are designed for enthusiasts who require extensive storage options, multiple graphics cards, and custom cooling solutions.

E-ATX motherboards require compatible computer cases with E-ATX support.

In addition to the mentioned form factors, there are specialized options like BTX and mini-STX. BTX never gained widespread popularity, while mini-STX is even smaller than mini-ITX and is focused on compact and low-power builds.

These form factors serve specific niches and may have limited availability and component options.

Selecting the appropriate motherboard form factor is crucial for a successful build. Consider factors like expansion needs, case compatibility, and available space to determine the most suitable option.

Ensure compatibility with your chosen case, power supply, and other components before making a final decision.