The answer to this question depends entirely on a number of factors. The two most important are:

  • How large is your backup?
  • How fast is your upload speed (bandwidth) to the internet?

Determine Your Bandwidth and Backup Size

Upload Bandwidth

Unlike the commonly understood download speed, it is the upload speed that matters most for cloud backups.

It is always a good idea to measure your upload speed. It is common for the actual speeds to differ greatly from the speed advertised by your Internet Service Provider (ISP). Speeds can vary based on a number of factors, including time of day.

To test your bandwidth, use a third-party speed test application or website, such as

Backup Size

ZCB includes a built in backup size estimation tool. To use it:

  1. Create your backup set.
  2. Choose the files and folders you wish to back up.
  3. Save your backup set.
  4. Click "Estimate Backup Size", located underneath the file/directory tree found in Backup What.

"Estimate Backup Size" displays the size of your Full, uncompressed backup. The actual upload size can be much smaller if you enable compression in the Backup How section, depending on the type of data to be compressed. Incremental and/or Differential backups will be smaller, too.

Bandwidth vs Backup Size

This chart estimates how long it will take to upload different amounts of data with common office connection types.

Cable/DSL bandwidth varies greatly by area and by provider, so always check your actual speeds to see where you fall on this chart!

Connection Type

Upload Speed

Upload 1 GB

Upload 5 GBUpload 10 GBUpload 25 GBUpload 100 GBUpload 1,000 GB
Cable/DSL (slow)

1 Mbps

2.4 hours12 hours1 day2.5 days10 days100 days

1.5 Mbps

1.6 hours8 hours16 hours1.7 days6.6 days66 days
Cable/DSL (fast)

5 Mbps

30 minutes2.4 hours4.8 hours12 hours2 days20 days
Fiber Optic

10 Mbps

15 minutes1.2 hours2.4 hours6 hours1 day10 days

45 Mbps

3.2 minutes16 minutes32 minutes1.3 hours5.3 hours2.2 days

156 Mbps

< 1 minute4.5 minutes9 minutes23 minutes1.5 hours15 hours

If you have a flaky or slow internet connection, we recommend to not use the "Backup to Cloud" operation. A Backup to Cloud operation introduces a great dependency between the backup and upload operations. Therefore, any performance issues in the upload operation will quickly become bottlenecks for the backup operation too.

Please refer to Info: Limitations of the Backup to Cloud operation.