Retrieval Chunk Size Calculator

Work out retrieval chunk size instantly with clear inputs, formula shown and shareable results.

About Retrieval Chunk Size Calculator

Sliding-window chunking advances by chunk size minus overlap, so the chunk count is roughly document length divided by that stride. Overlap protects facts that straddle a boundary but duplicates tokens, inflating both embedding cost and index size. The duplicated-token figure is the price you pay for that safety margin.

Formula

Sliding-window chunking

stride = chunk - overlap; chunks = ceil((document tokens - overlap) / stride); duplicated = chunks x chunk - document tokens

Worked example

With the default values below, Retrieval Chunk Size Calculator returns Chunks produced of 18. Change any input above and every figure here is recalculated in your browser.

Inputs used

Tokens in the documentminimum 1: 8,000
Chunk sizeminimum 16: 512
Overlap between chunksminimum 0: 64

Results

Chunks produced: 18
Tokens advanced per chunk: 448
Tokens stored more than once: 1,216
Overlap as a share of chunk size: 12.50%

Step by step

1Values used
2Sliding-window chunking
3Chunks produced= 18
4Tokens advanced per chunk= 448
5Tokens stored more than once= 1,216
6Overlap as a share of chunk size= 12.50

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What chunk size works best?

256 to 512 tokens suits precise question answering; 1000 or more suits summarisation and narrative context. Test both against your own evaluation set rather than guessing.

Is fixed-size chunking the best approach?

Splitting on structure first — headings, paragraphs, code blocks — then packing to a token budget usually retrieves better than blind fixed windows, because chunks stay semantically whole.