Need Help with Storage Capacity issue

Hey everyone I hope someone can help me figure this question out. I recently purchased the My Passport Ultra 4TB and was reformatting it to FAT32 so I can use on my mac and windows computer. Once formatting was done it is now saying i only have about 1.8tb space left why is that can someone please help thank you.

Hi RavenBug,

Please know that you have to format the drive in exFAT in order to make it compatible with both mac and windows and to use the capacity of the drive please format it in GPT/GUID partition map.

NOTE: Formatting is data destructive and cannot be undone.