How long will that download take?
A new game, a system update, a 4K movie or a cloud backup can run to tens or hundreds of gigabytes. Your internet plan’s speed tells you how fast data can flow, but it is quoted in a different unit from the file size, and real connections rarely hit their advertised peak. This calculator converts both and adds a realistic allowance for overhead.
Bits and bytes
Internet speeds are measured in megabits per second (Mbps). File sizes are measured in megabytes (MB) and gigabytes (GB). One byte is 8 bits, so:
- 100 Mbps moves at most 12.5 MB per second.
- 1 Gbps moves at most 125 MB per second.
Here a gigabyte is 1,000 megabytes, the convention used by internet providers and storage makers. Windows and some apps report sizes in binary gibibytes, which are about 7 percent larger.
The formula
- Effective speed = connection speed × (1 − overhead).
- Time in seconds = file size in megabytes × 8 ÷ effective speed in Mbps.
The overhead covers network protocols, Wi-Fi losses and other traffic. About 10 percent is typical on a good wired connection; use 20 to 40 percent on Wi-Fi far from the router.
Worked example: a 50 GB game on a 300 Mbps plan
- File size: 50 GB = 50,000 MB = 400,000 megabits.
- Effective speed: 300 × 0.90 = 270 Mbps, or 33.8 MB/s.
- Time: 400,000 ÷ 270 = 1,481 seconds = 24 minutes 41 seconds.
- At that pace, you download about 121.5 GB an hour.
The same 50 GB at other speeds
| Connection | Download time | Effective speed |
|---|---|---|
| 25 Mbps | 4:56:18 | 2.8 MB/s |
| 100 Mbps | 1:14:04 | 11.3 MB/s |
| 300 Mbps | 24:41 | 33.8 MB/s |
| 500 Mbps | 14:49 | 56.3 MB/s |
| 1 Gbps | 7:24 | 112.5 MB/s |
| 2 Gbps | 3:42 | 225.0 MB/s |
Why real downloads can be slower
- The server sets a ceiling. Game stores, cloud services and websites limit the speed of each download, especially on launch days.
- Wi-Fi. Walls, distance and interference often cut speed by half or more. A wired Ethernet connection gives the most reliable result.
- Your other devices. Streaming, video calls and backups share the same line.
- Your storage. An old hard drive can be slower than a gigabit connection, so installs may lag behind downloads.
Uploads and backups
Upload speeds are often much lower than download speeds on cable and DSL plans, sometimes 10 to 20 times lower. Fiber plans tend to be symmetrical. To estimate how long a first cloud backup will take, enter your upload speed from a speed test. A 1 TB backup at 20 Mbps upload takes more than five days of continuous transfer, which is why many backup services offer to ship a drive for the first copy.