Download Time Calculator
Exact download time from file size and connection speed.
What it does
Download time divides file bits by line bits per second. The classic puzzle is units: providers sell megabits per second while browsers count down megabytes, and eight bits make each byte, so a 100 Mbps line moves about 12.5 MB/s at best.
The tool above takes the file size in MB, GB, or TB with the speed in Mbps. It returns the duration in plain words with total seconds and the file size in megabits beside it.
The default of 1 GB (1000 MB decimal) at 100 Mbps is 8000 megabits over 100 per second: 80 seconds, or 1 min 20 s. Halving the speed doubles the wait; doubling the file does the same.
The decimal gigabyte follows NIST SI prefix references with the FCC broadband guides measuring consumer speeds the same way. Real transfers add protocol overhead plus wifi and server limits on top of this line rate.
How to use
- Enter the file size number.
- Pick MB, GB, or TB to match the file.
- Enter the connection speed in Mbps from a speed test.
- Read the duration first for the plan.
- Add margin for wifi and busy hours before promising a time.
Formula
- 8
- Bits per byte bridging file and line units.
- 1000
- Decimal MB per GB used here, matching line rates.
- Mbps
- Megabits per second of usable line speed.
Decimal gigabytes assumed (1 GB = 1000 MB), consistent with provider rates and the data storage page. Operating systems reporting GiB will show slightly smaller files than entered here.
Worked example
Example: 1 GB at 100 Mbps
Size 1 GB, speed 100 Mbps.
- Megabytes: 1 x 1000 = 1000 MB.
- Megabits: 1000 x 8 = 8,000 Mb.
- Seconds: 8000 / 100 = 80 s.
- Words: 80 s = 1 min 20 s.
- Tool shows 1 min 20 s, 80 s, 8,000 Mb.
Reference table
| Speed | Seconds | Duration |
|---|---|---|
| 25 Mbps | 320 s | 5 min 20 s |
| 100 Mbps | 80 s | 1 min 20 s |
| 1000 Mbps | 8 s | 8 s |
Limits
- Line rate only; overhead, wifi, and servers slow reality.
- Decimal GB assumed; GiB based sizes differ by about 7%.
- Speed tests vary by minute; retest for promises.
- Uploads use the slower upstream rate, not this one.
Common mistakes
- Dividing megabytes by megabits without the times 8.
- Reading MB/s browser figures as provider Mbps.
- Mixing decimal GB with binary GiB.
- Trusting one speed test at peak hours.
- Forgetting other devices share the line.
Try it yourself
Quick checks. Answers sit tucked under each question.
500 MB at 50 Mbps?
4000 / 50 = 80 s, 1 min 20 s.
2 GB at 25 Mbps?
16000 / 25 = 640 s, 10 min 40 s.
File megabits in 1 GB?
1000 x 8 = 8,000 Mb.
Questions
How long to download 1 GB at 100 Mbps?
80 seconds (1 min 20 s) at line rate: 8000 megabits over 100 per second.
Mbps vs MB/s?
Eight bits make a byte, so 100 Mbps moves at most 12.5 MB/s.
GB or GiB?
This page uses decimal GB (1000 MB) like providers. Systems showing GiB read about 7% smaller.
Why slower in reality?
Protocol overhead, wifi loss, busy servers, and shared lines all take a cut.
What about uploads?
Same math with the upstream rate, which usually runs far below download.
Does speed vary?
Yes by minute and hour. Test twice, then plan on the lower figure.