Why is 100 Mbps NOT 100 MB/s?
The most common confusion when shopping for internet plans. The ISP advertises "300 Mbps", but your 4 GB movie takes 2 minutes to download instead of 10 seconds. What went wrong?
Lowercase "b" means bit, uppercase "B" means byte. And 1 byte is 8 bits. ISP marketing uses bits (the bigger marketing number), files on your computer are in bytes. That's the 8× difference.
This tool converts every unit at once: bits, bytes, decimal, binary. Plus it computes a concrete download time for any file size at your connection speed.
How to use it
- Section 1, speed conversion: enter a value, pick a unit. The other units update automatically.
- The tool groups units in three blocks: bits (what ISPs advertise), bytes decimal (what browsers show), and bytes binary (what Windows shows).
- Click any tile to copy that value to clipboard.
- Section 2, file download time: enter file size and connection speed, get a concrete time.
- Use the presets: common files (photo, MP3, HD/4K movie, AAA game) and common speeds (LTE, fiber 100/300/1000 Mbps).
When this is useful
Classic questions this tool answers:
- "I have 300 Mbps fiber, why does a 4 GB movie take so long?". Because 300 Mbps is 37.5 MB/s, so 4 GB is about 2 minutes (in ideal conditions). Now it makes sense.
- Comparing ISP plans. "1 Gbps" sounds impressive. What's that in MB/s? 125 MB/s in ideal conditions, around 100 MB/s in practice.
- Show the difference to a friend (partner, kid, coworker). Lowercase b vs uppercase B is literally an 8× gap. The numbers don't lie.
- "Speedtest shows 95 Mbps, what does that mean?". Your downloads run at about 12 MB/s. A 1 GB file takes about 80 seconds.
- Decision to upgrade your plan. Switch from 100 to 300 Mbps for $10/month more? See how much time you'd actually save on real files (games, movies, backups).
- Planning a big game or update download. An 80 GB game on 100 Mbps takes nearly 2 hours. On 300 Mbps it's 35 minutes. Know that ahead so you don't plan a movie night right after.
If you want to convert other units (weights, lengths, temperatures), see our unit converter. And if you're just interested in file sizes (B vs KB vs MB vs GB), check the file size converter.
Questions and answers
Lowercase "b" means bit, the smallest unit of information. Uppercase "B" means byte, 8 bits joined together. ISPs advertise speed in bits (Mbps: megabits per second), because the number looks 8 times bigger. Computers and files are measured in bytes (MB: megabytes). Conversion: divide Mbps by 8 to get MB/s. 100 Mbps = 12.5 MB/s. 1 Gbps = 125 MB/s.