I've noticed that I ALWAYS seem to "lose" space on a flash drive, when I format it in Windows 7. Doesn't matter if I use the HP format tool, or just Windows' built-in format.
Somehow, the mfg is using a FAT32 formatting tool that formats out to more space.
At first, I thought that my testing with vconsole.com 's USB testing (low-level write/read tool) was causing the flash drive to remap bad sectors, and then a subsequent high-level format was showing the effects of that, but when I did that three times to three different flash drives, and their original and new format sizes were identical (Edit: Between the three flash drives - the after format size was smaller than the original though), I realized that it wasn't just bad sectors. (What are the odds that three flash drives have exactly the same number of bad sectors mapped out during a write pass?)
I figure it has to do with the offset that Win7 uses when formatting things, compared to XP and DOS.
Acer CloudBook AO1-131 | Intel Celeron N3050 "Cherry Trail" dual | 2GB DDR3L | 32GB eMMC | Intel HD graphics
Gigabyte Brix J1900 (3x) | Intel Celeron J1900 "Bay Trail" quad | GSkill 8GB DDR3L-1600 CAS9 | 300GB Intel 320 Series SSD | Intel HD graphics
ASRock Z170 Pro4S ATX (2x) | Intel Pentium G4400 "Skylake" @ 4.455Ghz | 2x4GB Avexir DDR4-2400 | Samsung SM951 128GB M.2 AHCI SSD | AMD Radeon HD 7950 3GB