The short answer
A 100 GB file has a theoretical minimum upload time of about 2 hours 13 minutes on a measured 100 Mbps upstream connection. A 1 TB file takes about 22 hours 13 minutes at the same speed. At 20 Mbps, those minimums become roughly 11 hours and 111 hours.
Those are arithmetic minimums, not promises. Protocol overhead, congestion, Wi-Fi quality, retries, browser resource limits, and rate limits can all make a real transfer slower. The most useful estimate starts with your measured upload speed—not the download number in your broadband advertisement.
Upload-time calculator
Estimate the theoretical minimum upload time
Real transfers take longer because of protocol overhead, retries, congestion, and provider limits.
Upload-time table
The table uses decimal units: 100 GB means 100,000,000,000 bytes and 1 TB means 1,000 GB. Times are rounded and exclude overhead.
| Measured upload speed | 100 GB theoretical minimum | 1 TB theoretical minimum |
|---|---|---|
| 10 Mbps | 22h 13m | 9d 6h 13m |
| 20 Mbps | 11h 7m | 4d 15h 7m |
| 50 Mbps | 4h 27m | 1d 20h 27m |
| 100 Mbps | 2h 13m | 22h 13m |
| 500 Mbps | 26m 40s | 4h 27m |
| 1,000 Mbps | 13m 20s | 2h 13m |
The calculation
Network speed is normally expressed in bits per second, while file size is normally expressed in bytes. Eight bits make one byte, so the basic calculation is:
seconds = file size in bytes × 8 ÷ upload speed in bits per secondFor a 100 GB file at 100 Mbps:
100,000,000,000 × 8 ÷ 100,000,000 = 8,000 seconds
8,000 seconds = 2 hours 13 minutes 20 secondsGB and GiB are not interchangeable. A decimal GB is 1,000,000,000 bytes; a binary GiB is 1,073,741,824 bytes. Check which unit your operating system and transfer provider display before comparing a calculated time with a real upload.
Why the real upload takes longer
Your upstream speed may be much lower
A connection sold as 1 Gbps may advertise its downstream capacity. Run a wired speed test at the place and time you will upload, and use the upstream result. If the speed fluctuates, plan with a conservative sustained figure rather than the best single sample.
Wi-Fi adds another variable
Distance, walls, interference, power-saving behavior, and other devices can interrupt a long browser upload. Ethernet does not make the internet connection faster than its upstream limit, but it removes several local sources of instability.
Encryption and packaging take time
If files are compressed, checksummed, or encrypted before upload, that work consumes CPU and local disk or memory. It may overlap with network transfer, but it should not be treated as free. Test the workflow with a representative smaller package when the deadline is tight.
Retries and protocol overhead are real
Every network protocol carries control data in addition to file bytes. Failed requests also have to be retried. A small percentage of overhead matters when the arithmetic minimum is already measured in hours or days.
Resumability changes the risk, not the line speed
A resumable upload does not make a 100 Mbps connection exceed 100 Mbps. It reduces the amount of completed work that must be repeated after an interruption.
Cloudflare's official R2 documentation distinguishes a single upload, which must restart as a whole after failure, from multipart upload, where failed parts can be retried. It recommends multipart upload for large files or when parallelism and resumability matter: Cloudflare R2 upload methods. Google Cloud documents the same broad recovery principle for resumable sessions: Google Cloud resumable uploads.
VaultDrop account uploads at or above 100 MiB use a multipart path. Recovery metadata is kept locally for up to seven days. After a refresh, the unchanged local file must be selected again and the account's encryption key unlocked before the browser can continue. Parts already accepted by storage do not need to be sent again.
A practical preflight
- Measure upstream speed over Ethernet when possible.
- Confirm the service's largest-file, storage, and recipient-download limits separately.
- Keep the source file unchanged until the upload completes.
- Prevent the computer from sleeping during the transfer.
- Leave local working space for packaging and verification.
- Use a checksum when byte-for-byte integrity matters.
- Tell the recipient the package size and expected download time.
When shipping a drive is the honest answer
Online transfer is not automatically the best choice. At 10 Mbps, the theoretical minimum for 1 TB is more than nine days. If the deadline is shorter, the connection is unreliable, or several terabytes must move once, an encrypted physical drive with tracked delivery may be more predictable. Account for preparation time, courier time, loss risk, and the need to exchange the decryption secret separately.
For an online workflow, compare the calculated duration with the cost of a restart. The longer the transfer, the more valuable multipart recovery becomes—even though it cannot change the underlying connection speed.