Backup Storage Calculator
Size a grandfather-father-son backup footprint from change rate and retention, split across warm and cold storage.
About Backup Storage Calculator
Incremental-forever backup stores one full copy plus the changed blocks behind every retained recovery point, so the footprint is driven by change rate and retention depth rather than by the size of the source. Long-retention monthly points each anchor a month of change, which is why they usually dominate the total even though they are the fewest in number, and why they belong in cold storage. Both prices are user-supplied list prices to confirm on the AWS Backup pricing page for your region. It explains the recurring surprise that protecting 2 TB needs closer to 18 TB of backup storage, and shows that trimming monthly retention moves the bill far more than trimming daily retention.
Formula
Backup Storage
footprint = full copy + Σ(recovery points x days covered x daily delta x unique-block factor), where daily delta = primary GB x change rate.
- daily delta
- New bytes written each day that a backup must capture
- unique-block factor
- Share of changed blocks that are new rather than re-changed
Worked example
With the default values below, Backup Storage Calculator returns Monthly Backup Cost of $384.40. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Primary data protectedminimum 0 GB
- 2,000 GB
- Daily change rateaccepts 0–100 %
- 3 %
- Share of changed blocks that change againaccepts 0–95 %
- 40 %
- Daily recovery points keptminimum 0 points
- 30 points
- Weekly recovery points keptminimum 0 points
- 8 points
- Monthly recovery points keptminimum 0 points
- 12 points
- Warm backup storage priceminimum 0 USD per GB-month
- 0.05 USD per GB-month
- Cold backup storage priceminimum 0 USD per GB-month
- 0.01 USD per GB-month
Results
- Monthly Backup Cost
- $384.40
- Total Backup Footprint
- 18,056 GB
- Warm Storage
- 5,096 GB
- Cold Storage
- 12,960 GB
- Footprint vs Primary Data
- 9.03 x primary
- Footprint in Bytes
- 18 TiB
Step by step
- 1Values used
- 2Backup Storage
- 3Monthly Backup Cost= 384.40
- 4Total Backup Footprint= 18,056 GB
- 5Warm Storage= 5,096 GB
- 6Cold Storage= 12,960 GB
- 7Footprint vs Primary Data= 9.03 x primary
- 8Footprint in Bytes= 19,387,482,374,144
Assumptions and limits
- The result is derived only from the 8 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
How is Backup Storage calculated?
footprint = full copy + Σ(recovery points x days covered x daily delta x unique-block factor), where daily delta = primary GB x change rate. Incremental-forever backup stores one full copy plus the changed blocks behind every retained recovery point, so the footprint is driven by change rate and retention depth rather than by the size of the source. Long-retention monthly points each anchor a month of change, which is why they usually dominate the total even though they are the fewest in number, and why they belong in cold storage. Both prices are user-supplied list prices to confirm on the AWS Backup pricing page for your region.
Why does Backup Storage matter?
It explains the recurring surprise that protecting 2 TB needs closer to 18 TB of backup storage, and shows that trimming monthly retention moves the bill far more than trimming daily retention.
What values do I need to enter?
This calculator takes 8 inputs: Primary data protected, Daily change rate, Share of changed blocks that change again, Daily recovery points kept, Weekly recovery points kept, Monthly recovery points kept, Warm backup storage price, Cold backup storage price. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Why does cutting daily retention barely help?
Each daily point only carries one day of change, while each monthly point carries about thirty. Dropping one monthly point removes as much storage as dropping thirty daily ones.