The size of a motherboard can easily be defined by how it looks, the dimension and more easily if you have the motherboard manual. But they come in 4 sized typicall
ATX - This is the most common motherboard size and measures 12 x 9.6 inches. It typically has several expansion slots, making it ideal for gaming or high-performance computers. Micro-ATX - This motherboard measures 9.6 x 9.6 inches. It has fewer expansion slots but can still accommodate most components. Mini-ATX - This is the smallest motherboard size, measuring just 6.7 x 6.7 inches. It is designed for small form factor (SFF) computers and is often used in home theater PCs or small gaming systems. E-ATX - This is a larger version of the ATX motherboard, measuring 12 x 13 inches. It has more expansion slots and is designed for high-end, multi-GPU systems