Index Size Estimator

Estimate index storage and the capacity effect of fill factor.

About the Index Size Estimator

Estimate the logical bytes needed for index keys and included columns, then account for unused space implied by a fill factor.

How to use it

  1. Enter the indexed row count and average key width.
  2. Optionally add the average size of included columns.
  3. Set a fill factor from 1 to 100 and estimate.

Estimation formula

Base bytes = rows × (key bytes + included bytes). Capacity with fill factor = base bytes ÷ (fill factor / 100).

Example

One million entries with 32 key bytes and 16 included bytes require 48 MB before fill-factor allowance.

Estimate note

This is an estimate. Actual results depend on database engine, configuration, compression, indexes, and workload. Page headers and tree structure are not modeled.