Download Time Calculator: File Size and Speed to Time
Enter a file size and a connection speed to see how long the download takes in hours, minutes and seconds. File sizes can be decimal (MB, GB) or binary (MiB, GiB), speeds are in bits per second, and a table compares the same file across common speeds.
KB, MB, GB and TB are decimal here (1 GB = 1,000 MB). Choose KiB, MiB, GiB or TiB if the size was counted in 1,024s.
A download time calculator estimates how long a file takes to download by dividing the file size by the connection speed. File sizes are counted in bytes and internet speeds in bits per second, so the size is first multiplied by 8. A 1 GB file on a 100 Mbps connection takes 80 seconds at best.
Download Time Formula: Bits vs Bytes
Download time (seconds) = file size in bits ÷ speed in bits per second. The step people miss is the unit change: one byte is 8 bits, so a speed of 100 Mbps (megabits per second) moves at most 12.5 MB (megabytes) each second, not 100. Here is the calculation for a 1 GB file at 100 Mbps, exactly as the calculator above does it.
| Step | Calculation | Result |
|---|---|---|
| 1. Size in bytes | 1 GB × 1,000,000,000 | 1,000,000,000 bytes |
| 2. Size in bits | 1,000,000,000 × 8 | 8,000,000,000 bits |
| 3. Speed in bits per second | 100 Mbps × 1,000,000 | 100,000,000 bits/s |
| 4. Divide size by speed | 8,000,000,000 ÷ 100,000,000 | 80 seconds (1m 20s) |
Shortcut: seconds = size in MB × 8 ÷ speed in Mbps. For 1,000 MB at 100 Mbps that is 1,000 × 8 ÷ 100 = 80 seconds. If the same file is 1 GiB (1,073,741,824 bytes) the answer is 85.9 seconds, which is why the unit you pick matters.
Download Time Calculator Results for Common File Sizes
The table shows best-case download times for five file sizes at five speeds, using decimal units (1 GB = 1,000 MB). Every cell matches what the calculator returns for the same inputs.
| File size | 10 Mbps | 50 Mbps | 100 Mbps | 500 Mbps | 1 Gbps |
|---|---|---|---|---|---|
| 100 MB | 1m 20s | 16s | 8s | 1.6s | 0.8s |
| 1 GB | 13m 20s | 2m 40s | 1m 20s | 16s | 8s |
| 5 GB | 1h 6m 40s | 13m 20s | 6m 40s | 1m 20s | 40s |
| 50 GB | 11h 6m 40s | 2h 13m 20s | 1h 6m 40s | 13m 20s | 6m 40s |
| 100 GB | 22h 13m 20s | 4h 26m 40s | 2h 13m 20s | 26m 40s | 13m 20s |
Download time is inversely proportional to speed: double the speed and the time halves. Ten times the file size at the same speed takes ten times as long.
MB vs MiB and Mbps vs MB/s: Which Unit Is Which?
Two different mix-ups cause wrong download estimates. One is bits against bytes (a factor of 8). The other is decimal against binary prefixes: a gibibyte is about 7.4% larger than a gigabyte. The definitions below are from the NIST reference on prefixes for binary multiples.
| Unit | Equals | Where you see it |
|---|---|---|
| 1 byte (B) | 8 bits | File sizes |
| 1 MB (megabyte) | 1,000,000 bytes | Storage devices, this calculator's MB |
| 1 MiB (mebibyte) | 1,048,576 bytes | Software that counts in 1,024s |
| 1 GB (gigabyte) | 1,000,000,000 bytes | Storage devices, this calculator's GB |
| 1 GiB (gibibyte) | 1,073,741,824 bytes | Software that counts in 1,024s |
| 1 Mbps (megabit per second) | 1,000,000 bits/s = 0.125 MB/s | Internet plans and speed tests |
| 1 MB/s (megabyte per second) | 8 Mbps | Download progress windows |
NIST notes that telecommunications always uses the megabit per second to mean 1,000,000 bits per second, while "megabyte" has been used for both 1,000,000 and 1,048,576 bytes. Some programs display binary sizes but label them MB or GB; if your file size came from one of those, choose MiB or GiB in the calculator.
Why Real Downloads Take Longer Than the Estimate
The result is a best case: it assumes every bit of the speed you enter carries file data for the whole transfer. The calculator does not apply an overhead or "real-world" factor, because the true loss depends on your connection. In practice a download can run slower for these reasons:
- Packet headers. Each packet carries addressing information as well as data. An IPv4 header and a TCP header are at least 20 bytes each (RFC 791, RFC 9293), and an IP packet on Ethernet is at most 1,500 bytes (RFC 894), so at least 40 of every 1,500 bytes, about 2.7%, are not file data.
- The server. A file cannot arrive faster than the other end sends it, whatever your own line speed is.
- Sharing. Other devices and apps using the same connection take part of the speed.
- Wi-Fi. Distance, walls and interference can lower the speed between the router and your device below the speed of the line.
For a closer estimate, enter a speed you measured with a speed test while connected the way you will download, rather than the headline speed of your plan.
How Connection Speed Changes Download and Upload Time
In March 2024 the US Federal Communications Commission raised its benchmark for high-speed fixed broadband to 100 Mbps download and 20 Mbps upload, up from the 25/3 Mbps benchmark it set in 2015 (FCC news release, March 14, 2024). On a 50 GB file that change is the difference between 4h 26m 40s at 25 Mbps and 1h 6m 40s at 100 Mbps. The same formula works for uploads: type your upload speed into the speed box. Sending a 1 GB file at 20 Mbps takes 6m 40s, five times as long as receiving it at 100 Mbps.
Tips for Faster Downloads
- Use a wired Ethernet connection for large files when you can, so Wi-Fi signal quality is not the limit.
- Pause other downloads, streams and cloud backups on the same network while a large file transfers.
- If one server is slow, try a mirror or a different time of day; the limit may be at the sending end.
- Run a speed test first and enter the measured figure above, so the estimate reflects the speed you actually get.
Last updated: October 2026
Frequently Asked Questions
How is download time calculated?
Download time = file size in bits divided by speed in bits per second. File sizes are given in bytes and speeds in bits, so the calculator multiplies the size in bytes by 8 and then divides by the speed. Example: 1 GB is 8,000,000,000 bits, and at 100 Mbps (100,000,000 bits per second) that takes 80 seconds.
Why is my actual download slower than calculated?
The calculator gives the best case for the speed you enter and applies no overhead or slowdown factor. Real transfers lose time to packet headers, Wi-Fi signal quality, other devices sharing the connection, and servers that send more slowly than your line can receive. Enter a speed you measured with a speed test, not the headline speed of your plan, for a closer estimate.
What is the difference between Mbps and MBps?
Mbps is megabits per second and is how internet speeds are quoted. MB/s (sometimes written MBps) is megabytes per second and is what download windows usually show. One byte is 8 bits, so 1 MB/s = 8 Mbps and a 100 Mbps connection moves at most 12.5 MB each second.
How long does it take to download a 1 GB file?
With 1 GB taken as 1,000 MB, the best-case time is 13 minutes 20 seconds at 10 Mbps, 2 minutes 40 seconds at 50 Mbps, 1 minute 20 seconds at 100 Mbps and 8 seconds at 1 Gbps. A slow server or weak Wi-Fi adds to these times.
Does this calculator account for upload speed?
It uses whichever speed you enter. The formula is the same in both directions, so type your upload speed into the speed box to get an upload time. Many home plans upload more slowly than they download (the FCC broadband benchmark adopted in March 2024 is 100 Mbps down and 20 Mbps up), so the same file can take longer to send than to receive.
Is my speed data kept private?
Yes. All calculations run in your browser. No data about your internet speed or file sizes is sent to any server.
How long does it take to download 100 GB?
A 100 GB file is 800,000,000,000 bits. At best that takes 8 hours 53 minutes at 25 Mbps, 2 hours 13 minutes at 100 Mbps, 26 minutes 40 seconds at 500 Mbps and 13 minutes 20 seconds at 1 Gbps.
Is 1 GB equal to 1000 MB or 1024 MB?
In decimal (SI) units 1 GB is 1,000 MB, or 1,000,000,000 bytes. The binary unit is the gibibyte: 1 GiB is 1,024 MiB, or 1,073,741,824 bytes, about 7.4% larger. Some software shows binary sizes but labels them GB. This calculator treats GB as decimal and offers GiB as a separate unit.