Download Time Calculator
How long a file takes to download or upload at a given speed, after overhead, and the speed it needs to arrive in time.
The share of the line that carries none of the file: at least 5% for TCP over Ethernet, and more with resent packets, a busy line, Wi-Fi or a slow server.
10 GB at 100 Mbps, with 10% overhead
14 minutes,
888.9 seconds
- 10 GB is 10,000,000,000 bytes, or 9.313 GiB.
- At 100 Mbps, less 10% overhead, the file moves at 90 Mbps: 11.25 MB/s, or 10.73 MiB/s.
- With no overhead: 13 minutes, 20 seconds.
KB to TB count 1,000 bytes, and KiB to TiB 1,024. Windows counts a file's size in 1,024s, and Chrome and Firefox a download's size and speed, while each writes KB, MB and GB: pick GiB for a size read off any of them, and MiB/s for a speed read off a browser.
10 GB at common speeds, with 10% overhead
| Connection | Speed | Time |
|---|---|---|
| 2 Mbps | 12 hours, | |
| 24 Mbps | 1 hour, | |
| 50 Mbps | 29 minutes, | |
| 100 Mbps | 14 minutes, | |
| 300 Mbps | 4 minutes, | |
| 1 Gbps | 1 minute, | |
| 2.5 Gbps | 35.6 seconds | |
| 10 Gbps | 8.9 seconds |
Mobile speeds are typical ones, which vary by country, network and year; the rest are what the link is rated at. Select a connection to time the file at its speed.
The speed a deadline needs
To download 10 GB within 1 hour, with 10% overhead, the line needs at least 24.69 Mbps: 3.086 MB/s, or 2.943 MiB/s.
How long a download takes
A download takes its size in bits divided by the speed left for the file: time = size × 8 ÷ (speed × (1 − overhead)). 10 GB is 80,000,000,000 bits, so at 100 Mbps it takes 800 seconds with nothing lost, and 888.9 seconds, or 14 minutes and 49 seconds, with 10% overhead.
Overhead takes a share of the line, so it divides the speed rather than adding to the time: with 50% overhead the same file takes 1,600 seconds, not 1,200. Over Ethernet, a full packet takes 1,538 bytes of line time to carry 1,460 bytes of the file, so TCP loses about 5%; resent packets, a busy line, Wi-Fi and the server's own limits can cost more.
A GB here is 1,000,000,000 bytes, as a Gbps is 1,000,000,000 bits per second. Windows, Chrome and Firefox count sizes in 1,024s while they write KB, MB and GB, so pick GiB for a size read off them: 10 GiB is 10.74 GB. To convert a speed between units, see the Bandwidth Converter, and for the units in depth, Mbps vs MB/s: network speed units explained.
Built and maintained by Meet Shah · Last updated
What this tool is used for
- Estimating how long a large file will take on a known connection.
- Deciding whether a download will finish before you need to leave.
- Comparing two connection speeds on the same file.
- Working out the speed needed to finish within a window.
- Sanity-checking a progress estimate that looks wrong.
Frequently Asked Questions
- Why does the calculation need a bits-to-bytes conversion?
- Because connection speeds are quoted in bits per second and file sizes in bytes. A 100 Mbps line moves 12.5 MB/s at best, so a 1 GB file takes 80 seconds with nothing lost to overhead; dividing the megabytes by the megabits gives 10 seconds, an answer eight times too short.
- Why is a real download slower than the line speed?
- Because headers share the line. Over Ethernet a full packet takes 1,538 bytes of line time to carry 1,460 bytes of the file, so TCP moves at most 94.9% of the rate. Lost and resent packets, a busy line, Wi-Fi and the server's own limit can take it lower still, which is what the overhead setting is for.
- Does it use 1000 or 1024 for the prefixes?
- Both: KB to TB count 1,000 bytes, as speeds count 1,000 bits, and KiB to TiB count 1,024. Windows writes KB, MB and GB for sizes it counts in 1,024s, as Chrome and Firefox do for a download's size and speed, so a size read off any of them is in GiB. A GiB is 7.4% more than a GB.
- Does latency affect download time?
- Little for one large file, once the transfer is under way. More for many small files fetched one at a time, since each waits at least one round trip before its first byte arrives. This page's estimate is for one file moving at a steady rate.
- Why is my upload so much slower than my download?
- Because most home connections are asymmetric by design: ADSL and cable give far more of the line to downloads than to uploads, while many fibre plans run at the same speed both ways. Time an upload at the plan's upload speed, not its download speed.
Common errors and gotchas
- Confusing bits with bytes, a factor of eight.
- Using the advertised line speed as achievable throughput, which protocol overhead reduces.
- Adding the overhead to the time, when it takes a share of the line: 10% overhead makes a download 11.1% longer.
- Mixing decimal and binary size prefixes, where a gigabyte may mean 10^9 or 2^30 bytes.
- Assuming a steady rate, when real transfers fluctuate substantially.
- Ignoring that the server or the disk may be the bottleneck rather than the link.