Backup Window
Calculate how long a backup job will take given data size and transfer rate.
About Backup Window
Backup duration is data volume divided by sustained transfer speed — the factor of 3.6 converts MB/s into GB/hr (3600 seconds/hr ÷ 1024 MB/GB ≈ 3.5, commonly rounded to 3.6 for planning purposes). Incremental backups only transfer data that changed since the last backup run, so the effective data volume is scaled down by the change rate, dramatically shortening the backup window compared to a full backup of the same dataset.
Formulas
Backup time (full)
hours = data_GB / (speed_MBps × 3.6)
Backup time (incremental)
hours = (data_GB × change_rate%) / (speed_MBps × 3.6)
Worked example
With the default values below, Backup Window returns Estimated Backup Time of 0.93. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Data Sizeminimum 0 GB
- 500 GB
- Sustained Backup Speedminimum 1 MB/s
- 150 MB/s
- Backup Typeone of Full Backup, Incremental Backup
- Full Backup
- Data Change Rateaccepts 0.1–100
- 10
Results
- Estimated Backup Time
- 0.93 hrs
- Estimated Backup Time
- 55.6 min
- Data Actually Transferred
- 500.00 GB
- Equivalent Full Backup Time (reference)
- 0.93 hrs
Step by step
- 1Values used
- 2Backup time (full)
- 3Backup time (incremental)
- 4Estimated Backup Time= 0.93 hrs
- 5Estimated Backup Time= 55.6 min
- 6Data Actually Transferred= 500.00 GB
- 7Equivalent Full Backup Time (reference)= 0.93 hrs
Assumptions and limits
- The result is derived only from the 4 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
Where does the 3.6 factor come from?
It converts a MB/s transfer rate into GB/hr: 3600 seconds per hour divided by 1024 MB per GB ≈ 3.52, commonly rounded to 3.6 for backup planning headroom. Dividing GB of data by (speed × 3.6) yields hours directly.
Why is my actual backup slower than this estimate?
This models a constant sustained speed, but real backups also spend time on snapshot creation, deduplication/compression processing, metadata cataloging, and verification — plus source storage I/O contention with production workloads can throttle the effective transfer rate below the device's rated speed.
How much faster is an incremental backup than a full backup?
Roughly proportional to the inverse of the change rate — a 10% daily change rate makes incrementals about 10x faster than a full backup of the same dataset, which is why most backup strategies run periodic fulls with daily incrementals in between.