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Download Speed Calculator
Use this download speed calculator to find out how fast a file actually downloaded. Enter the file size and how long the download took, and the tool gives your speed in Mbps, MB/s, KB/s and GB per hour — plus how long common downloads would take at that speed.
Time a real download with a stopwatch, or use the worked example below. Direction only changes the label — the maths is the same for uploads and downloads.
How it works
Download speed is simply size divided by time. If a file of a known size took a known time to arrive, dividing the two tells you the average speed of that transfer. This calculator does that division, then expresses the answer in the four units people actually meet: megabits per second (Mbps), megabytes per second (MB/s), kilobytes per second (KB/s) and gigabytes per hour (GB/hour).
The tricky part is bits versus bytes. A bit is a single 0 or 1, and a byte holds 8 bits. Internet providers advertise speeds in megabits per second (Mbps), with a small "b", while browsers and download managers usually show megabytes per second (MB/s), with a capital "B". The two numbers for the same connection differ by a factor of 8: 40.96 Mbps is the same speed as 5.12 MB/s. Mixing them up is the most common reason a speed test seems to disagree with a download window — they are both right, in different units.
The steps are: turn the file size into megabytes (multiply gigabytes by 1,024, or terabytes by 1,048,576), multiply by 8 to get megabits, and divide by the total time in seconds. Then MB/s is the Mbps figure divided by 8, KB/s is MB/s times 1,024, and GB per hour is the file size divided by the time in hours. The table under the result applies the same speed to three everyday downloads — a 100 MB app, a 1.5 GB movie and a 5 GB game — so you can judge what the number means in practice.
Direction does not change the maths. An upload of the same size in the same time gives the same speed, so the direction dropdown only changes the label on the result. What does change the result is the connection itself: Wi-Fi signal, other devices using the network, the time of day, and how busy the server is all affect a real download. For a fair check, close other downloads, test more than once, and use a large file, because a tiny file finishes before the connection reaches full speed.
Worked example
A 1.5 GB movie file finishes downloading in 5 minutes. How fast was the download?
Step 1: Turn the size into megabytes. 1.5 GB × 1,024 = 1,536 MB.
Step 2: Turn megabytes into megabits. 1,536 MB × 8 = 12,288 Mb.
Step 3: Turn the time into seconds. 5 minutes × 60 = 300 seconds.
Step 4: Divide size by time. 12,288 ÷ 300 = 40.96 Mbps.
Step 5: Convert to megabytes per second. 40.96 ÷ 8 = 5.12 MB/s. In kilobytes that is 5.12 × 1,024 = 5,242.88 KB/s, and over an hour the same pace would move 1.5 GB every 5 minutes, or 18 GB/hour.
Try it yourself: enter a file size of 1.5 GB and a time of 5 minutes, and press Calculate. The tool gives exactly the same answer — 40.96 Mbps (5.12 MB/s). At that speed a 100 MB app takes about 20 seconds, the 1.5 GB movie itself takes 5 minutes, and a 5 GB game takes about 16 minutes 40 seconds.
FAQ
How is download speed calculated from file size and time?
Divide the file size by the time it took to download. First turn the size into megabits: multiply megabytes by 8, or gigabytes by 8,192, because one byte holds 8 bits and one gigabyte holds 1,024 megabytes. Then divide by the time in seconds. A 1.5 GB file is 12,288 megabits, and over 300 seconds that is 12,288 divided by 300, or 40.96 Mbps.
What is the difference between Mbps and MB/s?
Mbps means megabits per second and MB/s means megabytes per second, and one byte holds 8 bits, so the numbers differ by a factor of 8. A speed of 40.96 Mbps equals 5.12 MB/s, because 40.96 divided by 8 is 5.12. Internet providers advertise in megabits per second, while browsers and download managers usually show megabytes per second, which is why the same connection can look like two different numbers.
Why is my real download slower than my advertised speed?
Advertised speeds are maximums under ideal conditions, not a promise for every download. The server you download from, the time of day, Wi-Fi signal strength, other devices on your network, and the overhead of the connection itself all cut into the result. A plan advertised at 100 Mbps often delivers 70 to 90 Mbps in practice, and a single busy server can be slower still. Test more than once and at different times to get a fair picture.
Is 1 GB equal to 1,000 MB or 1,024 MB?
This calculator uses 1 GB = 1,024 MB, the binary definition that operating systems and file managers use, so a file shown as 1.5 GB on your computer is 1,536 MB here. Some storage makers and internet providers use 1 GB = 1,000 MB instead, which makes their numbers look slightly bigger. The difference is about 2.4 percent, so it matters for exact work but not for a rough check of your connection.
What download speed do I need for streaming and gaming?
Standard video streaming needs about 5 Mbps, high-definition video needs about 10 to 15 Mbps, and 4K video needs about 25 Mbps. Online gaming itself uses very little bandwidth, usually under 5 Mbps, but game downloads are large, so a 5 GB game takes about 17 minutes at 40 Mbps and about 7 minutes at 100 Mbps. If several people stream at once, add their needs together and aim for a plan comfortably above the total.