Why are my LVM Partition Sizes Different to What I have Entered?

I'm trying to create a 64GB LVM partition for my root volume. lvcreate -L 64G volume0 -n lv_root However, when I start gnome-disks the partition is listed as 69GB? Incidentially this is the same size I get using: df -H How would I create a logical volume that is 64GB in size rather than 69GB? Is this something to do with GB vs GiB or is this a quirk of LVM?