I can't check it now, but I think it was 40mm. You can't really hear it from a closed case when it's at 50% speed, and at 100%, it's audible but not loud. There is a PWM connector, but I dislike RPM going up and down, so I set static speed. 50% speed is enough to keep low temps on any SSD.
As I mentioned in the review, you don't really need a cooler if your motherboard is equipped with a large heatsink. All mid-shelf or higher gaming motherboards have large heatsinks, and nearly every first (usually the one above the first PCIe slot) M.2 PCIe 5.0 socket has a proper heatsink, too. The GC PRO SSD runs in my AMD test PC on the GB X870E Pro ICE, and no fan is required.