File transfer time calculator
Enter a file size and a connection speed to see roughly how long a transfer will take, and learn why it is often slower than the number on your internet bill.
The calculator multiplies the file size by eight to turn bytes into bits, then divides by your connection speed. The efficiency field allows for real-world overhead. Protocol headers, encryption, Wi-Fi interference and other traffic on the line mean a transfer rarely runs at the advertised speed. 80% is a reasonable starting point for a good home connection, 50 to 60% for busy Wi-Fi or a weak mobile signal. Treat the result as an estimate, not a promise.
Mbps is not MB/s
This is the most common source of confusion. Internet speeds are sold in megabits per second (Mbps, lowercase "b"). File sizes are shown in megabytes (MB, capital "B"). One byte is eight bits, so a "100 Mbps" connection moves at most 12.5 megabytes per second. A 1 GB file on that line takes at least 80 seconds, not 10.
| Advertised speed | Maximum MB/s | 1 GB file | 10 GB file |
|---|---|---|---|
| 10 Mbps | 1.25 MB/s | ~13 min 20 s | ~2 h 13 min |
| 50 Mbps | 6.25 MB/s | ~2 min 40 s | ~27 min |
| 100 Mbps | 12.5 MB/s | ~1 min 20 s | ~13 min 20 s |
| 300 Mbps | 37.5 MB/s | ~27 s | ~4 min 27 s |
| 1 Gbps | 125 MB/s | ~8 s | ~1 min 20 s |
The table assumes a perfect line and decimal units (1 GB = 1,000 MB). Windows reports sizes in binary units (1 GiB = 1,073.7 MB), labelled as "GB". So a file Windows calls 10 GB is about 7% larger than the table assumes.
Which speed should I enter?
Enter the slowest link in the chain. For any transfer between two people, that's usually the sender's upload speed. Most home broadband, cable and mobile plans are asymmetric: download is fast and upload is a fraction of it. A plan sold as "500 Mbps" might upload at only 20 to 50 Mbps. Fibre plans are more often symmetric.
- Uploading to a cloud service (WeTransfer, Google Drive and so on): the sender's upload speed sets how long the upload takes. The receiver then downloads separately, using their own download speed.
- Direct peer-to-peer transfer (such as TransferFiles.net): there's one combined step. Data moves at the lower of the sender's upload and the receiver's download, so enter whichever is smaller. If the connection has to go through a relay server, the relay's capacity can also become the bottleneck.
- Between devices on the same Wi-Fi: a local-network tool can be much faster than your internet plan, because data doesn't leave your router. Expect real Wi-Fi throughput to be well below the router's headline figure.
To find your real numbers, run a speed test such as fast.com (click "Show more info" to see upload) or speedtest.net on the device you'll be sending from, on the network you'll actually use.
Why transfers are slower than the estimate
- Wi-Fi conditions. Distance from the router, walls, the 2.4 GHz band and neighbouring networks can cut throughput sharply. A cable, or simply moving closer, often helps more than anything else.
- Other traffic. Video calls, streaming, cloud backups and game downloads on either network share the same bandwidth.
- Distance and latency. Over long distances, round-trip delays limit how fast a single connection can ramp up, especially on lossy links.
- Device limits. Older phones and computers can be limited by storage write speed or the CPU work needed for encryption.
- Throttling. Some services slow free accounts, and some mobile plans slow traffic after a data allowance is used up. See what really limits transfer speed.
Worked example
You want to send 12 GB of wedding footage. Your fibre plan is 300 Mbps down and 50 Mbps up. Your client's cable connection is 200 Mbps down.
- Cloud upload, then download: your upload at 50 Mbps and 80% efficiency takes about 40 minutes. Their download at 200 Mbps takes about 10 more minutes, whenever they get round to it.
- Direct transfer: limited by your 50 Mbps upload, so about 40 minutes in total. You both need to stay online for those 40 minutes, but the client has the files the moment the transfer finishes.
Neither method is always better. The guide to sending large files to clients covers how to choose. If you'll be using mobile data, check how much data a transfer uses first.