Size and Allocated: Which Number Should You Use?

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Short answer: Use the measurement that matches your question: logical content length and occupied storage are different concepts.

By DiskAnalyzer editorial resource · Published 2026-10-05 · Documentation reviewed 2026-10-05

When this guide is useful

If two folders have similar content sizes but different physical footprints, compare file counts and storage attributes. Many small files, compressed data and placeholder files can produce very different relationships between the columns.

Recommended workflow

Display both size columns.
Compare a few individual files.
Check compression and sparse or cloud status where relevant.
Use the same column throughout a comparison.

Limits and precautions

Do not estimate recoverable space from logical sizes alone.

Keep a useful record

Record the drive or folder, scan time, application version and the measurement you used. Keep observations separate from proposed changes. If a result leads to a cleanup, record the file owner, backup status and actual free-space change. This makes the result easier to review and helps explain differences in a later scan.

Quick review checklist

Question	What to record
What did you inspect?	The exact volume or folder, not just the PC name.
What action is justified?	Use the same column throughout a comparison.
What could go wrong?	Do not estimate recoverable space from logical sizes alone.

Next steps

If the result is unclear, preserve the current report and narrow the investigation to one folder or application. Make one approved change at a time, then repeat the relevant measurement. Avoid presenting a predicted saving as a measured outcome.

Sources and verification

Prepared from public documentation and practical storage-audit reasoning. No hands-on Windows test or independent binary inspection was performed for this publication. Menu names and package requirements can change; check the developer documentation for your installed version.