Guide / Backup planning
How long does a 1 TB backup take?
At 20 Mbps upload, the theoretical minimum is about 4 days and 15 hours. Real throughput and your daily schedule can stretch it considerably.
The backup upload time calculator lets you enter your data size, upload speed, and availability instead of relying on a generic estimate.
Start with a lower bound
One decimal terabyte is 1,000,000,000,000 bytes, or eight trillion bits. Divide by upload bits per second to calculate the transfer duration. This assumes uninterrupted transfer at the full speed entered.
| Upload speed | At full speed | At 80% usable speed |
|---|---|---|
| 10 Mbps | 222.2 hours | 277.8 hours |
| 20 Mbps | 111.1 hours | 138.9 hours |
| 50 Mbps | 44.4 hours | 55.6 hours |
| 100 Mbps | 22.2 hours | 27.8 hours |
The 80% column is a scenario, not a promise about a provider or connection. Effective transfer rates may be much lower, especially when another part of the process is the bottleneck.
Use upload speed
An internet plan’s prominent speed may refer to downloads. For sending files to cloud storage, the relevant direction is upload. If a transfer application reports MB/s, multiply by eight to express decimal megabytes per second as Mbps.
Account for the hours you can actually upload
At 20 Mbps and an 80% usable share, 1 TB requires about 138.89 active hours. With eight hours available each day, it needs 18 upload windows. Assuming it begins at the start of the first window, 17 gaps of 16 hours bring elapsed time to about 410.89 hours, or 17 days and three hours.
If the transfer can run all day, those idle gaps disappear. That does not mean it should consume all available bandwidth: household use and other work may need headroom.
Check progress against the estimate
After a representative period, compare bytes actually sent with active transfer time. Recalculate using that effective throughput and 100% usable share; otherwise you would subtract overhead twice. Keep scanning and preparation time separate if the application reports it separately.
The daily backup is a different problem
Once the initial copy is finished, changed data determines the next upload. Model that amount independently. Also consider how a restore would work: downloading and verifying data is a separate task with different constraints. Finishing an upload alone does not demonstrate that the backup is recoverable.
Sources
NIST explains decimal and binary prefixes; Backblaze describes connection speed and initial-backup timing. The table and schedule examples are calculated here and are not measurements of a backup service. Methods and editorial policy.