Snapshot Size
Estimate storage snapshot size based on change rate and retention period.
About Snapshot Size
Copy-on-write and redirect-on-write snapshots only store blocks that changed after the snapshot was taken, so snapshot size grows roughly linearly with the daily change rate multiplied by how many days have elapsed since it was created — the longer a snapshot is retained, the more accumulated changes it must track, until in the worst case it approaches the full size of the source volume (every block has changed at least once).
Formula
Snapshot size
size = min(source_size, source_size × daily_change% × days_since_last)
Worked example
With the default values below, Snapshot Size returns Estimated Snapshot Size of 105.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Source Volume Sizeminimum 0 GB
- 500 GB
- Daily Data Change Rateaccepts 0–100
- 3
- Days Since Last Snapshotminimum 0
- 7
Results
- Estimated Snapshot Size
- 105.00 GB
- Daily Change Volume
- 15.00 GB
- Snapshot as % of Source Volume
- 21.0%
Step by step
- 1Values used
- 2Snapshot size
- 3Estimated Snapshot Size= 105.00 GB
- 4Daily Change Volume= 15.00 GB
- 5Snapshot as % of Source Volume= 21.0
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why does the calculator cap the snapshot at the source volume size?
A copy-on-write snapshot can never store more changed data than the source volume actually contains — once every block has been overwritten at least once since the snapshot was taken, the snapshot has effectively captured a full copy and further growth stops.
Why do old snapshots often cause storage alerts?
Because snapshot size grows with elapsed time, a snapshot left in place for weeks or months accumulates far more changed-block overhead than a short-lived one — this is why most storage platforms recommend deleting or consolidating snapshots on a schedule rather than leaving them indefinitely.
Does a higher daily change rate always mean the snapshot fills up faster?
Yes — the daily change rate is the dominant driver of snapshot growth; a volatile volume (databases, active VMs) with a high change rate will consume much more snapshot space per day than a mostly static volume (archives, templates), even at the same retention period.