Enter a file size and time.
Speed & transfer
Download Speed Calculator
Worked out how long a file took to download? Get your real speed in Mbps and MB/s, and see how it compares with your plan.
Short answer: download speed in Mbps equals file size in megabytes times 8, divided by the seconds it took. This calculator does that maths for you and also shows the MB/s number your browser uses.
Why measure it this way?
Speed test websites use their own servers and often finish in a few seconds. A real download shows how your connection behaves with the file you actually care about, from the server you actually use. That is a useful second opinion when a game update or a movie feels slow.
The formula
Mbps = MB × 8 ÷ seconds. The 8 is there because every byte holds eight bits and providers sell speed in bits. Divide the Mbps figure by 8 and you are back to MB/s, the number shown in most download windows.
Example
A 500 MB file that arrives in 45 seconds works out to 500 × 8 ÷ 45, about 88.9 Mbps or 11.1 MB/s. If your plan is 100 Mbps, you received roughly 89% of it, which is a very healthy result.
Why you may get less than your plan
Plans are sold as “up to” a number. Wi-Fi distance, busy servers, other devices and a bit of protocol overhead all take a slice. Try the optional plan box: it shows your result as a percentage so you can tell normal from worrying.
- Over 80% of the plan: everything is fine.
- 50 to 80%: normal on Wi-Fi or at busy hours. Try a cable.
- Under 50% on a cable at a quiet time: worth contacting your provider.
Going the other way? The Download Time Calculator tells you how long a file will take at a given speed.
FAQ
Frequently asked questions about the Download Speed Calculator
How do I calculate download speed from file size and time?
Multiply the file size in megabytes by 8 to get megabits, then divide by the time in seconds. A 100 MB file in 10 seconds is 100 × 8 ÷ 10 = 80 Mbps.
What is the difference between Mbps and MB/s?
Mbps is megabits per second, used for plans. MB/s is megabytes per second, used by downloads. One byte is eight bits, so 80 Mbps is about 10 MB/s.
Why is my real download slower than my plan?
Plans quote a maximum. Wi-Fi quality, the other end of the download, shared use at home and overhead all reduce it. Test over a cable at a quiet hour to see the true ceiling.
Should I use a big file or a small one?
Bigger is better. Very small files finish before the connection reaches full speed, which makes the result look lower than it really is. Aim for a file that takes at least 20 seconds.
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Use this toolResults are estimates for planning. Last reviewed 2 October 2026.