How it works
Updated August 12, 2026 · min read
Why File Size Alone Cannot Prove Two Files Are Identical
Use byte count as a fast filter, not a content identity test.
Byte size feels persuasive because highly different files often have different lengths. But size contains no information about the values of those bytes: two generated exports, fixed-size database pages, or small text files can collide in length by chance.
Use size as an index. It partitions the inventory and avoids comparing fingerprints for files that cannot be exact. Within each size bucket, compare the same content-fingerprint algorithm and value.
A practical checklist
- 1Exclude files with different byte counts from exact comparison.
- 2Create candidate buckets for equal sizes.
- 3Compare supported fingerprints within each bucket.
- 4Keep missing-hash candidates in a review-only state.
- 5Use path and sharing only for retention choice.
Understand the situation
Byte size feels persuasive because highly different files often have different lengths. But size contains no information about the values of those bytes: two generated exports, fixed-size database pages, or small text files can collide in length by chance.
Keep detection evidence separate from retention judgment. Technical signals can establish that bytes match, while path, permissions, history, and ownership determine whether one file item is operationally redundant.
Use a controlled workflow
Use size as an index. It partitions the inventory and avoids comparing fingerprints for files that cannot be exact. Within each size bucket, compare the same content-fingerprint algorithm and value.
A robust pipeline handles pagination, missing values, throttling, and changes during the scan. Incomplete data should lower confidence or remain unresolved instead of being converted into a clean-looking but unsafe result.
- Create candidate buckets for equal sizes.
- Compare supported fingerprints within each bucket.
- Keep missing-hash candidates in a review-only state.
Make the final decision
Display size-only relationships as candidates or diagnostics, never as safe-to-remove groups. If no supported fingerprint exists, leave the item unresolved or use a separately disclosed content comparison.
ClearCopies has a deliberately narrow promise: scan supported cloud metadata, confirm exact candidates by byte size plus a matching provider fingerprint, let the user review, and export the plan without downloading original content.
Limits and risks to check
- — Same-size false positives are common enough to matter at scale.
- — Zero-byte files all share a size but may have distinct purpose.
- — Name plus size still does not prove equality.
- — An exact match does not identify the canonical item.
Official references
Frequently asked questions
Is different size enough to rule out an exact copy?
Yes. Byte-identical files must have the same byte count.
Is same size plus same extension enough?
No. The extension describes format, not the complete byte sequence.
Why not compare every hash directly?
Size bucketing reduces work and provides a simple consistency check while retaining fingerprint confirmation.
Scan first. Decide with evidence.
ClearCopies reads supported cloud-drive metadata and groups exact copies by byte size plus a provider-supplied content fingerprint. Original file bodies are not downloaded for the scan. You review the result and export a plan before any separate write step.