Choose a size and a speed to see the transfer time, or a size and a deadline to see the speed required. Adjust real-world efficiency and parallel streams, and enter the round-trip time to check the TCP window limit.
Bandwidth and Transfer Time Calculator
How long will a transfer take, or how fast a link do you need? With real-world efficiency and TCP window limits.
Protocol overhead and congestion usually leave 85 to 95% of the line speed for data.
1 GB at 100 Mbps, 90% efficiency
1 min 29 s
Effective throughput 90.0 Mbps (11.3 MB/s)
Typical transfers at 100 Mbps
| Photo (4 MB) | 356 ms |
| Song (10 MB) | 889 ms |
| HD movie (4 GB) | 5 min 56 s |
| Game install (60 GB) | 1 h 28 min 53 s |
| Laptop backup (500 GB) | 12 h 20 min 44 s |
| Server backup (2 TB) | 2 d 1 h 22 min |
Sizes use decimal units (1 MB = 1,000,000 bytes) unless you pick the binary units KiB, MiB, GiB or TiB. Speeds are in bits per second; MB/s means megabytes.
About the bandwidth and transfer time calculator
Work out how long a file transfer will take at a given connection speed, or how fast a link you need to move data in a set time. This bandwidth calculator allows for real-world efficiency and parallel streams, and shows how round-trip time and the TCP window limit a single connection.
Also searched as: file transfer time calculator · download time calculator · data transfer calculator · bandwidth calculator · internet speed time calculator · upload time calculator · network throughput calculator
Bits, bytes and the factor of eight
Line speeds are quoted in bits per second (Mbps) and file sizes in bytes (MB). One byte is eight bits, so a 100 Mbps link moves at most 12.5 MB per second. The calculator converts between them and offers both decimal units (MB, GB) and binary units (MiB, GiB).
Why real transfers are slower
Headers, retransmissions and congestion mean a link rarely carries more than 85 to 95 percent of its rated speed as useful data. The efficiency slider models this, so the estimate matches what you will see instead of the theoretical best case.
Long-distance links and TCP windows
On a path with high latency a single TCP connection can only have one window of data in flight per round trip, so throughput is capped at window divided by round-trip time. A 64 KB window over 100 ms tops out near 5 Mbps however fast the link is. Enter the round-trip time to see the bandwidth-delay product and the limit; the cure is window scaling or several parallel streams.
How this tool works and how to read the results
Frequently asked questions
How long does it take to download 1 GB at 100 Mbps?
About 80 seconds in theory (1 GB is 8,000 megabits), and roughly 90 seconds with typical protocol overhead.
What is the difference between Mbps and MB/s?
Mbps is megabits per second, MB/s is megabytes per second. Divide Mbps by eight to get MB/s.
Why is my transfer slower than my line speed?
Overhead, server limits, Wi-Fi, a long round-trip time with a small TCP window, or a bottleneck elsewhere on the path. Test with several parallel streams to see whether latency is the limit.
What is the bandwidth-delay product?
Bandwidth multiplied by round-trip time: the amount of data that must be in flight to keep a link full. If your TCP window is smaller than this, the link cannot be filled by one connection.