Database Index Size Estimator
Use this as a first-pass storage budget for indexes. Index entry size varies with key width, included columns, page fill, compression and the database engine.
How to use this calculator
- Enter the number of table rows using the units shown beside the field.
- Enter the average bytes per index entry using the units shown beside the field.
- Enter the number of indexes being estimated using the units shown beside the field.
- Review the calculated values and check that the assumptions match your scenario.
- Change one input at a time when comparing scenarios so you can see which assumption drives the result.
Formula and assumptions
Estimated bytes = row count × bytes per entry × index count × (1 + overhead percentage).
- This is a capacity estimate, not a database-engine measurement. Validate it against the system’s catalog or actual index-size statistics.
- The result is computed from the values you provide; it does not fetch external rates, live account data or local rules.
Worked examples
Worked example
2.5 million rows × 48 bytes × four indexes with 25% overhead estimates about 0.56 GiB.
Example inputs: Number of table rows = 2500000, Average bytes per index entry = 48, Number of indexes being estimated = 4, Additional overhead allowance (%) = 25.
Compare the displayed output with your own measurements before using it in a decision.
Understanding the result
This is a capacity estimate, not a database-engine measurement. Validate it against the system’s catalog or actual index-size statistics.
Results are estimates based on the stated model. If the situation depends on measured conditions or contractual specifications, use those source values rather than typical assumptions.
Important notes
This is a capacity estimate, not a database-engine measurement. Validate it against the system’s catalog or actual index-size statistics.
Frequently asked questions
What formula does this calculator use?
It uses the method described above: Estimated bytes = row count × bytes per entry × index count × (1 + overhead percentage).
What should I verify before relying on the result?
This is a capacity estimate, not a database-engine measurement. Validate it against the system’s catalog or actual index-size statistics.
Can I compare different scenarios?
Yes. Change the inputs while keeping units and definitions consistent, and record the assumptions used for each scenario.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.