Backup Storage Calculator
Planning backup storage capacity requires accounting for your data size, daily change rate, backup type (full vs. incremental), retention period, compression, and deduplication ratios. Under-estimating storage leads to failed backups and data loss exposure; over-estimating wastes storage budget. This calculator estimates total backup storage requirements for a grandfather-father-son (GFS) rotation policy with daily, weekly, and monthly backups, applying compression and deduplication to give a realistic provisioned storage figure in terabytes.
Backup storage formula
full_compressed = data_TB / compression_ratio
daily_incr = data_TB * (change_rate/100) / compression_ratio
full_copies = weekly_retain + monthly_retain
total = (full_copies * full_compressed) + (daily_retain * daily_incr)
provision = total * 1.25 (25% buffer)
Backup storage best practices
- Follow the 3-2-1 rule: 3 copies, 2 media types, 1 offsite location.
- Test restores regularly - a backup is only as good as its last successful restore test.
- Use immutable storage (WORM) for offsite backups to protect against ransomware that targets backup systems.
- Monitor backup job completion rates and alert on any failures the same day they occur.
- Document your recovery time objective (RTO) and recovery point objective (RPO) and verify that your backup strategy meets them.
Frequently asked questions
What is the 3-2-1 backup rule?
The 3-2-1 rule means keeping 3 copies of your data on 2 different storage media types with 1 copy stored offsite. This strategy protects against hardware failure (the second copy on different media), local disasters such as fire or flood (the offsite copy), and ransomware (air-gapped or immutable offsite backups).
How do full, incremental, and differential backups differ?
A full backup copies all data. An incremental backup copies only data changed since the last backup of any type. A differential backup copies all data changed since the last full backup. Incremental backups use the least daily storage but require the full backup plus all incrementals to restore. Differential backups are faster to restore but grow larger each day until the next full backup.
What compression ratio should I expect for backups?
Compression ratios depend heavily on data type. Databases and text files compress well, achieving 3:1 to 5:1 ratios. Office documents compress at 2:1 to 3:1. Already-compressed files such as JPEG images, video, and ZIP archives compress poorly, at 1:1 or less (no benefit). A mixed enterprise environment typically averages 1.5:1 to 2.5:1 compression.
What is backup deduplication and how does it reduce storage?
Deduplication identifies duplicate data blocks across multiple backups and stores each unique block only once. This is particularly effective for virtual machine backups (where many VMs share the same OS files) and file shares where many users store copies of the same documents. Deduplication can reduce backup storage by 5:1 to 30:1 in enterprise environments.
How long should I retain backups?
Retention requirements depend on regulatory and business requirements. HIPAA-covered healthcare entities must retain certain records for 6 years. SOX compliance requires 7 years for financial records. Most businesses use a grandfather-father-son (GFS) rotation: daily backups for 7-14 days, weekly backups for 4-8 weeks, and monthly backups for 12 months.
Official sources
- NIST: SP 800-34 Rev 1 - Contingency Planning Guide for Federal Information Systems.
- CISA: Data Backup Options.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.