IP and InternetHow to use it
- Type the size of the file and choose its unit. Game and film sizes are usually in GB, photos and songs in MB.
- Type your speed. Internet plans and speed tests give Mbps. If your browser or download program is showing a speed such as "6.2 MB/s", choose MB/s instead.
- Read the time. It updates as you type.
For an upload, type your upload speed, which on many connections is much lower than the download speed.
The arithmetic
Time = size ÷ speed, once both are in matching units. The catch is that sizes are in bytes and line speeds are in bits, and a byte is 8 bits.
seconds = (size in megabytes × 8) ÷ speed in Mbps
Example: a 4.7 GB file on a 50 Mbps line. 4.7 GB is 4,700 MB. 4,700 × 8 = 37,600 megabits. 37,600 ÷ 50 = 752 seconds, which is 12 minutes 32 seconds.
The calculator uses decimal units, as internet providers and storage makers do: 1 GB = 1,000 MB, 1 MB = 1,000 KB. Windows counts in units of 1,024 and so shows a "4.7 GB" file as about 4.38 GB. The file is the same; only the ruler differs.
Quick reference: megabytes per second
| Line speed | Moves each second | Moves each hour |
|---|---|---|
| 2 Mbps | 0.25 MB | 0.9 GB |
| 10 Mbps | 1.25 MB | 4.5 GB |
| 40 Mbps | 5 MB | 18 GB |
| 100 Mbps | 12.5 MB | 45 GB |
| 200 Mbps | 25 MB | 90 GB |
| 1 Gbps | 125 MB | 450 GB |
Why a real download takes longer
The result is the time at a perfectly steady speed. In practice:
- Speed varies from second to second, and usually starts slow before climbing.
- Other devices in the house share the line.
- Wi-Fi may be slower than the line itself. Compare a speed test beside the router with one where you sit.
- The server at the other end may send more slowly than your line can receive, especially at busy times or from far away.
- Overheads: a few percent of every connection is addressing and checking, not your file.
- Your disk: on very fast lines, an old hard disk or a busy phone may not write as fast as data arrives.
A fair rule is to add a tenth to a fifth to the calculated time, and more on Wi-Fi.
Using it the other way round
- Will the pack last? The "data moved in one hour" line tells you how much a steady stream at that speed uses. A video playing at 5 Mbps uses 2.25 GB an hour.
- Is my plan delivering? If your browser shows 3 MB/s on a 100 Mbps plan, choose MB/s and type 3: that is only 24 Mbps. See why results fall short of the plan.
- How long will the backup take? Type the total size of your photos and your upload speed. Large first backups often take days on slow upload lines, which is normal.
How long does 1 GB take at 10 Mbps?
About 13 minutes 20 seconds: 1,000 MB × 8 ÷ 10 = 800 seconds.
Is Mbps the same as MB/s?
No. Divide Mbps by 8 to get MB/s. A 100 Mbps line moves 12.5 MB each second at best.
Why does my download show KB/s?
The server or your connection is slow at that moment. 1,000 KB/s is 1 MB/s, which is 8 Mbps.