Mbps vs MB/s: How Fast Will My Download Actually Be?
Internet plans are sold in megabits (Mbps) but downloads show megabytes (MB/s). Divide by 8 to convert, then estimate how long a file will take to download.
The short answer
Mbps means megabits per second; MB/s means megabytes per second. There are 8 bits in a byte, so divide Mbps by 8 to get MB/s. A 100 Mbps connection can download at most about 12.5 MB/s, and a browser or game launcher that counts in binary units will show about 11.9. You can check any figure with the Data Storage Converter by converting Megabit to Megabyte.
Bits vs bytes in one minute
- A bit (lowercase b) is a single 0 or 1. Network speeds are measured in bits per second: Kbps, Mbps, Gbps.
- A byte (uppercase B) is 8 bits. File sizes and download progress are measured in bytes: KB, MB, GB.
So "100 Mbps" and "100 MB/s" are very different. The second is eight times faster. Internet providers advertise in megabits; your downloads folder, Steam, a browser or a phone's app store usually show megabytes.
Conversion table
The middle column uses decimal megabytes (1 MB = 1,000,000 bytes). The right column uses binary megabytes (1 MB = 1,048,576 bytes), which is what the Lazyblink converter and many operating systems use.
| Plan speed | MB/s (decimal) | MB/s (binary) |
|---|---|---|
| 10 Mbps | 1.25 | 1.19 |
| 40 Mbps | 5.00 | 4.77 |
| 50 Mbps | 6.25 | 5.96 |
| 100 Mbps | 12.50 | 11.92 |
| 200 Mbps | 25.00 | 23.84 |
| 300 Mbps | 37.50 | 35.76 |
| 500 Mbps | 62.50 | 59.60 |
| 1 Gbps (1,000 Mbps) | 125.00 | 119.21 |
These are the theoretical maximums. Real downloads are slower, for the reasons below.
How to convert with the Data Storage Converter
The converter treats Kbit, Mbit and Gbit as decimal units (1 Mbit = 1,000,000 bits) and KB, MB and GB as binary units (1 MB = 1,048,576 bytes). That matches how speeds are usually advertised and how Windows reports file sizes, but it is why its answer is 11.92 rather than 12.5. If your download manager shows decimal megabytes, simply divide the Mbps figure by 8. For why the two kinds of megabyte exist, see Why a 1 TB Drive Shows 931 GB.
How long will a download take?
Use this formula with decimal units:
Time in seconds = file size in GB × 8,000 ÷ speed in Mbps
The 8,000 converts gigabytes to megabits (1 GB = 1,000 MB = 8,000 megabits).
| File | Speed | Best-case time |
|---|---|---|
| 1.5 GB film | 50 Mbps | 240 seconds (4 minutes) |
| 5 GB game update | 100 Mbps | 400 seconds (about 6 minutes 40 seconds) |
| 50 GB game | 300 Mbps | about 1,333 seconds (about 22 minutes) |
Treat these as minimum times. In practice expect longer.
The same maths for uploads
Uploads work the same way, but many plans have a lower upload speed than download speed, so check the upload figure on your plan or speed test. Sending a 2 GB video to cloud storage on a 20 Mbps upload takes at least 2 × 8,000 ÷ 20 = 800 seconds, about 13 minutes 20 seconds, even though the same file would download in under 3 minutes on a 100 Mbps download line.
A shortcut to remember
Divide by 8, then knock off a little. A 1 Gbps plan tops out around 125 MB/s, a 300 Mbps plan around 37 MB/s, and a 40 Mbps plan around 5 MB/s.
Why real downloads are slower than your plan
Even if your connection is working perfectly, several things reduce the speed you see:
- Wi-Fi. Distance from the router, walls and interference from neighbouring networks can cut speed sharply. A wired connection, or standing near the router, gives a fairer test.
- Other devices. A TV streaming in 4K or a phone backing up photos shares the same connection.
- The server. A download is limited by the slower end. A busy game server or website may send data more slowly than your line can receive it.
- Protocol overhead. Some of each transfer is used for addressing and error checking rather than your file, so usable throughput is a little below the raw line rate.
- Upload vs download. Many plans have a lower upload speed. Sending a large file can take much longer than downloading the same file.
A quick check
If your download shows roughly your plan speed divided by 8, minus a modest margin, your connection is doing what it should. If it is far lower even on a wired connection with nothing else running, test at different times of day and contact your provider with the results.
Common mistakes
- Reading Mbps as MB/s. Expecting a 100 Mbps plan to download 100 MB every second leads to the belief that the internet is "eight times too slow".
- Multiplying instead of dividing. Going from megabits to megabytes, the number gets smaller. If it got bigger, you went the wrong way.
- Mixing decimal and binary. 12.5 and 11.9 are both correct answers for 100 Mbps; they use different definitions of a megabyte. Compare like with like.
- Ignoring the capital letter. Mb and MB look similar. On routers, speed tests and plan brochures, check whether the b is lower or upper case.
Related tools and guides
- Convert file sizes between KB, MB, GB and TB with the Data Storage Converter.
- Shrinking a photo to fit an upload limit: Compress Image to KB.
Frequently asked questions
What is 100 Mbps in MB per second?
100 Mbps is 12.5 MB/s using decimal megabytes, or about 11.92 MB/s using binary megabytes. Divide megabits by 8 to get megabytes.
Is Mbps the same as MB/s?
No. Mbps is megabits per second and MB/s is megabytes per second. One byte is 8 bits, so MB/s is eight times larger than the same number in Mbps.
How long does it take to download 5 GB at 100 Mbps?
At best about 400 seconds, roughly 6 minutes 40 seconds: 5 × 8,000 ÷ 100. Real downloads usually take longer.
Why is my download speed lower than my internet plan?
Plans are sold in megabits while downloads show megabytes, and Wi-Fi, other devices, the server and protocol overhead also reduce real speed.
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