What cluster size does a FAT/NTFS partition use?

John Savill

January 8, 2000

1 Min Read
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A. The default cluster size for a FAT partition is as follows:

Partition size

Sectors per cluster

Cluster size

<32MB

1

512 bytes

<64MB

2

1K

<128MB

4

2K

<255MB

8

4K

<511MB

16

8K

<1023MB

32

16K

<2047MB

64

32K

<4095MB

128

64K

This is why FAT volumes larger than 511MB are not recommended due to the amount of potentially wasted space due to the 16KB and above cluster size.

The default for NTFS is as follows:

Partition size

Sectors per cluster

Cluster size

<512MB

1

512 bytes (or hardware sector size if greater than 512 bytes)

<1024MB

2

1K

<2048MB

4

2K

<4096MB

8

4K

<8192MB

16

8K

<16384MB

32

16K

<32768MB

64

32K

>32768 MB

128

64K

NTFS better balances the trade off between disk defragmentation due to smaller cluster size and wasted space due to a large cluster size.

When formatting a drive you can change the cluster size using the /a: switch, e.g.

format d: /a:1024 /fs:ntfs

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