gigabyte h270 gaming 3 can add 6 gpu or no ?
Your motherboard only got
1 x PCI Express x16 slot, running at x16 (PCIEX16)
1 x PCI Express x16 slot, running at x4 (PCIEX4)
2 x PCI Express x1 slots
and 2 x PCI slots that can not be use for GPU.
With that max you can go is 4 GPU.
But if you use the other 2 x M.2 connector (using converter to pcie), you can at 2 more GPU with total 6 GPU
(of course I don't know if it really work with your motherboard), but maybe some of our member here know about that.