What should you do if you ordered a mini-ATX motherboard but your existing case uses an ATX form factor?

Using a mini-ATX motherboard in an ATX case is a practical solution because ATX cases are designed to accommodate various motherboard sizes, including mini-ATX. The mini-ATX motherboard will fit inside the ATX case without any issues, as there is typically more space available in ATX cases. This option allows you to utilize the hardware you already have without needing to return parts or purchase a new case.

The configuration will not only save you from the hassle of returning the motherboard but also allows for better airflow and additional features that an ATX case may provide, like extra drive bays or expansion slots. This flexibility is one of the notable advantages of using an ATX case compared to a mini-ATX case, which would restrict future upgrade options.

Other alternatives, such as returning the motherboard or switching to a mini-ATX case, would involve additional costs and effort that may not be necessary. Modifying the motherboard is not advisable either, as it can lead to damage or void warranties. Therefore, utilizing the mini-ATX motherboard in your existing ATX case is the most efficient and practical approach.