Calculate how long a backup job will take given data size and transfer rate.
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.
Backup time (full)
hours = data_GB / (speed_MBps × 3.6)
Backup time (incremental)
hours = (data_GB × change_rate%) / (speed_MBps × 3.6)
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.
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.
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.