Bandwidth and download-time calculator
Find how long a file takes to transfer, or the link speed you need to move it in time.
Calculated in your browser. Nothing is sent to our servers.
Enter a file or backup size and a link speed to see how long the transfer will take. Add a target time to find the speed you would need instead. Use it to size an internet link, check whether a nightly backup will finish before morning, or explain to users why a 10 GB file takes as long as it does.
Bits versus bytes
Link speeds are quoted in bits per second, file sizes in bytes. One byte is eight bits, so a 100 Mbps link moves at most 12.5 megabytes per second. That is why a 1 GB file takes about 80 seconds on a perfect 100 Mbps link.
Why real transfers are slower
TCP/IP headers, encryption, Wi-Fi contention and latency all reduce throughput. The overhead field accounts for this: around 5–10% on a clean wired link, 20–40% on busy Wi-Fi or long-distance VPNs. Long-distance links also suffer from TCP window limits, so a single stream may never fill a fast link.
Decimal and binary units
Storage vendors use decimal units (1 GB = 1,000,000,000 bytes) while operating systems often show binary units (1 GiB = 1,073,741,824 bytes). Pick the unit that matches the number you have.
Common questions
How long does 1 GB take on 100 Mbps?
About 80 seconds at full line rate, or roughly 90 seconds with 10% protocol overhead.
Why is my download speed in MB/s lower than my plan?
Plans are sold in megabits per second. Divide by eight to get megabytes per second: a 200 Mbps plan downloads at up to 25 MB/s.
What overhead should I use?
Use 5–10% for wired Ethernet and fibre, 20–30% for Wi-Fi and 15–25% for IPsec or SSL VPN tunnels.
