Why file size and free disk space differ on Windows
Compare logical size, allocated space, cloud placeholders and duplicate files before choosing a Windows disk analyser or cleanup tool.
Start with the question you need answered
A folder-size chart answers where file contents are concentrated. A volume capacity reading answers how much space Windows currently reports as available. A duplicate report answers which files have matching contents. These are useful but different measurements; adding every number in a cleanup list does not predict the change in free space.
Read logical and allocated size separately
Logical size describes the amount of data represented by a file. Known allocated size describes storage assigned to it, where the filesystem exposes that information. Compression, sparse files and hard links make the relationship less direct. Unknown allocation must stay unknown; a tool should not silently substitute a confident estimate.
Recognise cloud placeholders
A visible OneDrive filename may be online-only. Opening it or choosing Always keep on this device downloads its contents and consumes local space. Free up space makes a synced file online-only. These operations change local availability; they are not an independent backup. Check provider status and keep the source until a separate copy is verified.
Inspect a small folder before scaling up
Choose one folder you understand. Compare its largest files with what you expect, inspect skipped or unreadable entries, and check whether the view uses logical or allocated sizes. A scan is an observation while files may be changing. Re-run it after substantial changes instead of treating an old chart as the current disk state.
Review duplicates and recovery
Matching names are weak evidence. Compare full contents and distinguish hard links from independent copies. Keep a deliberate original, review project references, and retain a separate backup. Moving an item to the Recycle Bin usually keeps its bytes on the same volume; do not treat that action alone as reclaimed capacity.
Choose a focused analyser or a broader file workspace
The SpaceLens Windows candidate concentrates on sunburst/treemap exploration and reviewed cleanup. Indep File Manager combines browsing, structured search, storage and verified copy workflows. Both pages describe their actual Windows limits and preparation status. Choose by your recurring task rather than the longest feature list.