Backup Storage Calculator

See how much storage a retention policy takes, and what it costs each month and to pull one full restore back out, at the prices you've been quoted.

Inputs

Protected data

The size of one full backup before deduplication or compression.

Data change per day

The size of a typical daily incremental backup, before data reduction.

Restore points kept

How many of each restore point your policy keeps, for example 14 daily, 4 weekly, 12 monthly and 0 yearly.

Daily

Weekly

Monthly

Yearly

Data reduction ratio (n:1)

Deduplication and compression together, applied to everything stored. 1 means none. Use the ratio your backup system reports for this data; it varies widely with data type and how many full copies you keep.

Your prices (optional)

From your quote or your provider’s price sheet. No prices are built in. Some providers bill binary gigabytes (2³⁰ bytes); this calculator counts decimal ones.

Prices are per

Storage, $ a month

Retrieval and egress, $

A full restore reads

Retrieval and egress are billed on the bytes that leave storage. If the data is expanded before it leaves, that is the full size; if your backup software pulls the reduced data and expands it on site, it is the stored size.

Result

Enter the protected data and the daily change to see the storage your retention needs.

Related Tools

Backup Restore Time Calculator
Find out how long it would take to get all your data back from backup, and whether that meets your recovery time target.
RPO and RTO Calculator
Set how much data and time you can afford to lose for each system, and see what kind of protection that takes.
Replication Bandwidth Calculator
Find out how much bandwidth you need to copy changed data to a second site or the cloud and meet your recovery point target.
Uptime and SLA Calculator
See how much downtime an uptime percentage really allows, and what an outage is worth in SLA credits.
Data Transfer Time Calculator
Find out how long it will take to move your data over a network link, or how fast a link you need to hit a deadline.

How the calculation works

One simplified model, full plus incrementals with grandfather-father-son (GFS) retention:

One full copy of the protected data: the oldest daily restore point, the base the others build on.
One incremental for each of the other daily restore points, each holding one day’s change.
One full copy for each weekly, monthly and yearly restore point kept.

Total before reduction = protected data × (1 + weekly + monthly + yearly) + daily change × (daily points − 1).

Storage needed = total before reduction ÷ data reduction ratio (deduplication and compression together, n:1).

The model counts every weekly, monthly and yearly point as its own full copy and doesn’t model overlaps between them or data growth over the retention period, so for most setups the result is an upper bound. A daily change given as a percentage is taken of the protected data.

Costs, at your prices only. No published prices are built in.

Monthly storage = storage needed × your price per GB or TB a month.
One full restore = the data read back × your retrieval and egress price per GB or TB. The data read back is the full (logical) size, or the stored size (÷ the ratio) if your backup software pulls the reduced data and expands it on site.

Units. Sizes are decimal (1 GB = 10⁹ bytes, 1 TB = 10¹² bytes). Some providers bill binary gigabytes (2³⁰ bytes, about 7% larger), so a bill can differ slightly from the result.

Worked example

50 TB protected, 2% daily change, keeping 14 daily, 4 weekly, 12 monthly and 1 yearly restore point, with 4:1 data reduction. The prices are illustrations, not market rates: $5 per TB a month for storage and $20 per TB to retrieve.

Daily change: 2% of 50 TB = 1 TB
Full copies: 1 base + 4 weekly + 12 monthly + 1 yearly = 18 × 50 TB = 900 TB
Incrementals: the base full is the oldest daily point, so 13 × 1 TB = 13 TB
Total before reduction: 913 TB; at 4:1, 228.25 TB of storage
Monthly storage: 228.25 TB × $5 = $1,141.25
One full restore reading the full 50 TB: 50 × $20 = $1,000.00

If the backup software reads the stored data instead, the restore reads 50 TB ÷ 4 = 12.5 TB. With the same prices quoted per GB ($0.005 per GB a month and $0.02 per GB to retrieve), the monthly cost is the same $1,141.25 and one full restore costs $250.00.

Frequently Asked Questions

Why do monthly and yearly restore points take so much space?

In this model each weekly, monthly and yearly point is a full copy of the protected data, so keeping 12 monthly points means 12 more full copies. Daily points after the first are incrementals and add only a day's change each. Deduplication is what keeps long retention affordable in practice, which is why the ratio you enter matters so much.

What reduction ratio should we enter?

The one your backup system reports for this data, if you have it. Ratios vary widely: databases, documents and virtual machines reduce differently, and already-compressed or encrypted data hardly reduces at all. Deduplication also gets better the more full copies share the same blocks. Without a measured figure, try 1 (no reduction) and a modest ratio to see the range.

Why include retrieval and egress prices?

Low-cost storage tiers often charge to read data back or to move it out of the provider's network, and archive tiers usually charge more to retrieve than standard tiers. Those fees don't show up until you restore, which is often the worst time to find out. The calculator prices one full restore at the rate you enter so you can compare tiers on the whole cost.

Does the calculator model forever-incremental backups?

No. It uses one simple model, full plus incrementals, with every weekly, monthly and yearly point counted as its own full copy. Forever-incremental backups with synthetic fulls that share blocks usually need less. The single reduction ratio stands in for that sharing, so for most setups the result is an upper bound.

How does the 3-2-1 rule change the storage needed?

The 3-2-1 rule calls for three copies of the data on two kinds of media with one copy off-site. Each backup copy you keep needs its own storage, so run the calculator once for each copy with its own retention and prices: an on-site copy might keep 14 days while the off-site or immutable copy keeps the monthly and yearly points.