Just go to the Properties of the Floppy disk by right-clicking on it and clicking on Properties. This will tell you the total space of the disk and how much of that is free.
I recommend picking up a USB Flash drive (thumb drive). Floppy disks are virtually obsolete because of them being too small and unreliable.
Most new computers do not include floppy disk drives any more. A few companies will sell you one if you need it, but they will range in cost from $30-$50 (US).
The amount of space on the floppy disk (1.44 MB) is do the number of sectors which can be fit on the physical media based on the standard which was approved many years ago.