MiB to KiB Converter for Block, Cluster and Chunk Sizes

Working Between MiB and KiB on Block and Cluster Sizes

Every layer of a storage stack picks its own favourite unit. The RAID array is configured with a chunk in mebibytes, the filesystem is formatted with a block in kibibytes, the tuning parameters that tie the two together are expressed as counts of blocks, and the alignment advice in the vendor's document is in yet another. Getting an array to write whole stripes instead of suffering read-modify-write means putting all of those numbers into the same unit first, and KiB is usually where they meet.

A mebibyte holds exactly 1 024 kibibytes, so multiply by 1 024. A 2 MiB chunk is 2 × 1 024 = 2 048 KiB, which is 512 filesystem blocks when the block size is the usual 4 KiB.

The 4 KiB Anchor

The x86 memory page, the ext4 default block, the NTFS default cluster and the physical sector of a modern drive all land on 4 KiB. Most alignment maths starts from that number.

Chunks Are Configured in MiB

Array chunk and stripe settings are habitually written as 64K, 256K or 1M. Converting them into KiB is what lets you count how many blocks fall inside one chunk.

Allocation Is All or Nothing

A file never occupies part of a block. Whatever the smallest allocation unit is, every file rounds up to a whole number of them — and the remainder is simply lost.

The choice is made once, at format time, and cannot be revised afterwards without rebuilding the filesystem. That is why it is worth doing the arithmetic carefully rather than accepting whatever the installer proposes, particularly on a volume that will hold either millions of tiny files or a handful of enormous ones.

Converting an Allocation Unit Before You Format

The two fields update each other as you type, which suits the back-and-forth of working out a stride and stripe-width before committing to a format.

Enter the Chunk in MiB

Type the array's chunk or stripe size on the left. Fractions are fine — a 64 KiB chunk is 0.0625 MiB, and the field accepts a comma just as readily as a dot for the decimal mark.

Read the KiB Figure

The kibibyte value appears at once on the right. Divide it by your filesystem block size to get the stride: 64 KiB over a 4 KiB block gives a stride of 16.

Take the Number to the Command Line

The copy button on each field hands you the bare value with no unit attached — ready to paste into a mkfs invocation or a format dialog that wants a plain figure.

Drop to Bytes When a Tool Insists

Some utilities take only a byte count. Change the unit on either side using the searchable dropdown and the same input answers in bytes without you retyping anything.

Going the other way: the swap button reverses to KiB → MiB, which is the direction you want when a tuning guide quotes a full stripe width in kibibytes and you need to check it against a chunk setting expressed in mebibytes. Both fields are editable in any case, so typing a kibibyte figure into the right-hand side produces the mebibyte equivalent without swapping.

Filesystem Block and Stripe Sizes in KiB

These are the sizes that actually appear in format commands and array configurations, listed in both units so a chunk expressed one way can be checked against a block expressed the other.

Allocation unit	MiB	KiB
Default ext4 block and NTFS cluster	0.00390625 MiB	4 KiB
Larger cluster for media volumes	0.015625 MiB	16 KiB
Common software-RAID chunk	0.0625 MiB	64 KiB
Chunk tuned for sequential workloads	0.25 MiB	256 KiB
Full stripe, six data members at 64 KiB	0.375 MiB	384 KiB
Large-file chunk setting	1 MiB	1 024 KiB
Upper end of NTFS allocation units	2 MiB	2 048 KiB
Wide stripe on a large array	4 MiB	4 096 KiB

The relationship worth memorising sits in the third row: a 64 KiB chunk over a 4 KiB block is sixteen blocks, which is the stride value the filesystem needs so its metadata does not all pile onto one array member.

Fractions Handled Cleanly

Sub-mebibyte units such as 0.00390625 MiB are ordinary input here, and results carry up to eight decimals so a small block size never collapses to zero.

Chunk and Block Side by Side

Two live panels let you keep the array's chunk on one side and the filesystem's block on the other while you work out how many blocks fit in a chunk.

Down to the Sector

Searchable unit lists on both sides reach all the way to single bytes, which is what alignment checks against a 512-byte logical sector need.

Runs Where You Work

All the arithmetic happens in the browser after load, so array layouts from a production system are never transmitted anywhere.

Allocation Unit Questions

Why is 4 KiB the default block size on almost every filesystem?

Because it matches the memory page size on the architectures that dominate. A filesystem block that equals a page maps straight into the page cache with no splitting or padding, which keeps the read and write paths simple and fast. Drives reinforce the choice: modern disks use 4 KiB physical sectors internally, so a 4 KiB block that starts on a 4 KiB boundary never straddles two sectors. It is a convergence of three separate constraints rather than an arbitrary default.

How much space do many small files waste on a 4 KiB block?

On average half a block per file, and it adds up quickly. Take a hundred thousand files averaging 1.5 KiB each: the data itself is 150 000 KiB, but each file claims a whole 4 KiB block, so 400 000 KiB is allocated. The 250 000 KiB difference — a little over 244 MiB — is slack space that nothing can use. Multiply that by a source tree, a mail spool or a cache directory holding millions of entries and the argument for a smaller block, or for packing the files into archives, becomes concrete.

Can I format ext4 or XFS with a block larger than 4 KiB?

The on-disk formats allow it, but Linux has long refused to mount a filesystem whose block size exceeds the machine's page size — so on ordinary x86-64 hardware 4 KiB remains the practical ceiling, and mkfs.ext4 -b 8192 produces something you cannot mount there. Going smaller is well supported: -b 1024 or -b 2048 cuts slack space on a volume full of tiny files at the cost of more metadata and a lower maximum filesystem size. XFS behaves the same way, defaulting to 4 KiB with the same page-size constraint on the upper end.

How should the RAID chunk size relate to the filesystem block size?

The chunk should be a whole multiple of the block, and the filesystem should be told the ratio so it can spread its allocation groups across the members. In ext4 terms that is stride, the number of blocks in one chunk, and stripe-width, the number of blocks in a full stripe across the data members. A 64 KiB chunk on a 4 KiB block gives a stride of 16; with five data members the stripe-width is 80. Get it wrong and metadata clusters on a single disk, which shows up as one array member running noticeably hotter than the rest.

When is a large NTFS allocation unit worth choosing?

When the volume will hold large, mostly sequential files and little else — capture scratch space, disk images, video assets. A 64 KiB or larger cluster cuts the number of allocation records the filesystem has to track, which keeps fragmentation manageable on a volume of very large files. The trade-offs are real, though: slack space grows in proportion to the cluster, and NTFS file compression is unavailable above 4 KiB clusters. For a general-purpose volume with a mixed file population, the 4 KiB default is still the right answer.