Computing total space on FAT16

Hi all,

I'm using CF storage (FAT16) in an embedded system, and i'm unable to
retrieve the remaining free space value given by XP.

Windows XP say :

Used space : 51200 bytes.
Free space : 16 283 848 bytes.
Total space: 16 334 848 bytes.

Ok, so let's see at the partition record :

Bytes per sector : 512
Sectors per cluster : 4
Reserved sectors : 1
FATs : 2
Root dir entries : 512
Sectors on drive : 32004
Sectors per FAT : 32
Hidden sectors : 63

Respecting the partition record, the first cluster (dataSector) is
located =E0 sector 152 :

FATsector =3D bootSector+ reservedSectors
rootSector =3D FATsector + nbOfFAT*sectorsPerFAT
dataSector =3D rootSector + (maxRootDir*32)/(bytesPerSector)

The total free space available is [Bytes per sector]*{[Sectors on
drive]-152 +1}, no ?
Computing :
512*(32004-152+1) =3D 16 308 736 !!!

Any ideas on how XP compute total space on disk ?