Database & SQL
PostgreSQL Index Size Estimator
Enter row count, key size, and index type to estimate index disk size, with fill factor and partial index adjustments. Covers B-tree, GIN, Hash, and BRIN.
No data is transmitted — everything runs locallyTool
About this tool
PostgreSQL Index Size Estimator
The PostgreSQL Index Size Estimator computes expected index disk size from row count, key size, index type, fill factor, and partial index coverage.
• Estimate index size before adding to a large production table with limited disk
• Compare B-tree vs BRIN index size for an append-only time-series table
• Calculate partial index savings for a column with a highly selective WHERE clause
• Model total index storage for a table with multiple indexes
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FAQ
What does this tool tell you?
The PostgreSQL Index Size Estimator computes expected index disk size from row count, key size, index type, fill factor, and partial index coverage.
What affects the result most?
B-tree index size estimate: rows × (key_size + 8 bytes overhead) / fill_factor × 1.3 bloat factor. GIN index (JSONB, full-text): typically 2-3× larger than B-tree on same column due to posting lists. Partial index savings: WHERE clause reduces index to fraction of full table size.
How should I use the result?
The calculation is deterministic — the same inputs always produce the same output — so the most useful workflow is to vary one input at a time and see which factor moves the result most. That tells you where to focus your attention before committing to a decision.
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