How do I check if my RAM will fit under my CPU cooler?

Measure or look up the clearance between your CPU cooler and the motherboard’s RAM slots, then compare with the RAM’s height. Most air coolers have a “RAM clearance” spec in millimeters—if the cooler overhangs the slots, tall RAM heatsinks won’t fit. For liquid coolers, check your specific AIO model’s RAM clearance. The simplest method is to measure the gap between your cooler’s bottom edge and the motherboard, then check the RAM’s height spec (tall kits are usually 40-50mm; standard is ~32mm). Don’t guess—that’s how you end up with a fan resting on a heatspreader and a system that won’t boot.