Backup Storage Calculator
Calculate backup storage requirements from source data volume, daily change rate, retention policy, and compression ratio using a GFS backup model.
About this calculator
This calculator sizes storage using a classic Grandfather-Father-Son (GFS) retention scheme rather than assuming every day's backup is a full copy. Daily incrementals capture only the data that changed — source volume times your daily change rate percentage — and one incremental is stored for every day of your retention window. On top of that, a weekly full backup runs once every seven days (calculated as retention days divided by 7, rounded up) and a monthly archive full runs roughly once every 30 days, both sized at the full source volume rather than just the delta. All three categories get divided by your compression ratio before being summed into total storage, then converted to TB.
This is why the model matters: naively multiplying source size by retention days would wildly overstate storage for low-change-rate data (a file server changing 1-2% daily barely grows its incremental footprint) while underestimating it for high-full-backup-frequency policies. The calculator also derives a required network throughput figure, assuming the largest single transfer — a full backup — must complete inside an 8-hour backup window, which is useful for confirming your backup network segment or WAN link can actually keep pace. Cost is split between a "hot" tier for incrementals and weekly fulls ($0.023/GB/month, roughly standard cloud object storage) and a cheaper archive tier for monthly fulls ($0.01/GB/month). Two things commonly trip people up: the compression ratio is applied uniformly to fulls and incrementals alike, and this model doesn't add overhead for deduplication metadata, indexes, or catalog data — plan roughly 30% extra headroom on top of the raw total for those.
Inputs
Results
Total storage (TB)
1.83
How to Use This Calculator
- Enter source data (GB) and daily change rate (%) -- typical: 3-5% for databases, 1-2% for files.
- Set retention period (days) and compression ratio -- 2:1 for text, 1.1:1 for already-compressed data.
- Review total storage needed in TB, incremental backup storage per day, and full backup size.
- Add 30% overhead to storage estimates for deduplication metadata, indexes, and catalog data.
- Plan for offsite or cloud replication -- 3-2-1 rule: 3 copies, 2 media types, 1 offsite.
How the result changes with Retention period (days)
| Retention period (days) | Total storage (TB) |
|---|---|
| 15 | 1.16 |
| 23 | 1.5 |
| 45 | 2.75 |
| 75 | 4.33 |
What each input means
- Source data (GB)
- Total volume of production data to back up, in gigabytes.
- Daily change rate (%)
- Percentage of source data that changes each day (typically 2-10% for databases, 1-3% for file servers).
- Retention period (days)
- Number of days to retain backup copies. Compliance may require 90-365 days.
- Compression ratio
- Expected compression ratio (2:1 is typical; databases may achieve 3-4:1, media files ~1.1:1).
What each result means
- Total storage (TB)
- Total backup storage required in terabytes across all retention tiers.
- Total storage (GB)
- Total backup storage in gigabytes.
- Incremental backups (GB)
- Storage consumed by daily incremental backups.
- Full backups (GB)
- Storage consumed by weekly and monthly full backups.
- Peak throughput (Mbps)
- Network bandwidth needed to complete a full backup in an 8-hour window.
- Avg daily transfer (GB)
- Average data transferred per incremental backup.
- Est. monthly cost ($)
- Estimated cloud storage cost (hot tier $0.023/GB + archive $0.01/GB per month).
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersSource data (GB) = 500, Daily change rate (%) = 5, Retention period (days) = 30, Compression ratio = 2 = 4 input(s) provided
- Calculate Total storageTotal storage = totalStorageGB / 10241.83 = 1.83
- Calculate Total storageTotal storage = incrementalStorageGB + weeklyFullStorageGB + monthlyFullStorageGB1875 = 1875
- Calculate Incremental backupsIncremental backups = dailyIncrementals * compressedIncrementalGB375 = 375
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why is total storage more than just source data times retention days?
The calculator uses a Grandfather-Father-Son model that stores three separate categories: a daily incremental (only the changed data) for every day of retention, a weekly full backup at the complete source size every 7 days, and a monthly archive full every ~30 days. Because the weekly and monthly fulls are sized at the entire source volume rather than just the daily delta, a 30-day retention window on 500 GB with a 5% daily change rate produces noticeably more total storage than 30 incrementals alone would suggest.
Does raising the compression ratio reduce incremental and full backup storage equally?
Yes -- the calculator divides both the full-backup size and the daily incremental size by the same compression ratio before summing them into total storage, so a higher ratio shrinks every retention tier proportionally. In practice this uniform assumption can be optimistic: compression ratios often differ between mostly-static full backups and the smaller, more randomized incremental deltas, which this model doesn't distinguish.
Why does the calculator care about an 8-hour backup window for throughput?
Peak required throughput is derived by assuming the largest single transfer -- a full backup at the complete source data size -- has to finish inside an 8-hour window, converting that GB figure into Mbps. This tells you whether your backup network segment or WAN link can actually move a full backup fast enough, since a link sized only for daily incremental traffic can be badly undersized on full-backup days.
Why are monthly full backups priced differently from weekly fulls and incrementals?
Incrementals and weekly fulls are billed at a 'hot' storage rate ($0.023/GB/month, roughly standard cloud object storage) because they need to stay quickly accessible for near-term restores, while monthly archive fulls are billed at a cheaper $0.01/GB/month archive tier since they're accessed far less often. This split reflects how cloud providers actually price storage tiers and can meaningfully lower cost if your monthly fulls make up a large share of total volume.
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