When to use this calculator
Retention policy and backup type can affect storage much more than the size of a single current dataset.
Explore the storage & compression calculators for other questions in this topic. For a related calculation, use the Backup Transfer Window Calculator: Estimate transfer time for a decimal-gigabyte backup over a sustained payload link.
PUTTING IT INTO PRACTICE
Backup Storage: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Source data per full backup (GB) | 100 |
| Retained full backups (integer) | 7 |
| Stored fraction after compression (%) | 60 |
| Result | 420 GB |
- Check the input labels and enter the example values above.
- Apply the relationship: Storage = source size × retained backups × stored fraction/100.
- The result is 420 GB, rounded for display.
How to interpret your result
Models full backups only. Incremental chains, deduplication, growth and metadata are excluded.
Specify decimal or binary units before comparing storage totals. Full-backup retention differs from incremental or deduplicated backup plans. Compression can sometimes increase size when data is already compressed.
Frequently asked questions
Is a 4:1 compression ratio a 400% saving?
No. It means the compressed size is one quarter of the original, corresponding to a 75% size reduction.
When is the backup storage calculator useful?
Retention policy and backup type can affect storage much more than the size of a single current dataset.
How do I use the backup storage calculator?
Enter source data per full backup (gb), retained full backups (integer), stored fraction after compression (%). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Storage = source size × retained backups × stored fraction/100.
What should I check before using the result?
Models full backups only. Incremental chains, deduplication, growth and metadata are excluded.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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