File Size & Download Time Calculator
Free file size and download time calculator. Convert bytes, KB, MB, GB, TB and estimate download time at your connection speed. No signup.
What the file size calculator does
It estimates how long a file will take to download at a given connection speed, and converts between file-size units. The reason a download often feels slower than the headline speed suggests is a units mismatch: file sizes are measured in bytes, but connection speeds are quoted in bits, and there are eight bits to a byte. This tool applies that factor for you.
How the calculation works
- File size: your value is converted to bytes using decimal units — 1 kB is 1,000 bytes, 1 MB is 1,000,000, and so on.
- Speed: the connection speed is converted to bits per second. 1 Mbps is 1,000,000 bits per second; 1 MB/s is 8,000,000 bits per second.
- Download time = file size in bytes × 8 ÷ speed in bits per second.
Note that this tool uses decimal size units. The unit converter and most operating systems use binary units, where 1 MB is 1,048,576 bytes. That difference is why a “750 MB” download can take slightly longer than a decimal calculation predicts.
A worked example
A 750 MB file on a 50 Mbps connection:
| Step | Calculation | Result |
|---|---|---|
| File size in bytes | 750 × 1,000,000 | 750,000,000 bytes |
| Speed in bits/s | 50 × 1,000,000 | 50,000,000 bps |
| Download time | 750,000,000 × 8 ÷ 50,000,000 | 120 s = 2m 0s |
Fifty megabits per second is only 6.25 megabytes per second, because of the factor of eight. That is the whole reason a fast-looking connection still takes minutes on a large file.
More download estimates
| File | Speed | Time |
|---|---|---|
| 750 MB | 50 Mbps | 2m 0s |
| 750 MB | 100 Mbps | 1m 0s |
| 5 GB | 100 Mbps | 6m 40s |
| 1.5 GB | 25 Mbps | 8m 0s |
Speed to throughput conversion
| Connection | Bytes per second |
|---|---|
| 10 Mbps | 1.25 MB/s |
| 50 Mbps | 6.25 MB/s |
| 100 Mbps | 12.5 MB/s |
| 1 Gbps | 125 MB/s |
Common mistakes
- Reading Mbps as MB/s. An 8× overestimate is the single most common download-time error.
- Confusing decimal and binary units. Drive makers use decimal; your operating system usually shows binary, so a “1 TB” drive displays less.
- Expecting the full advertised speed. Wi-Fi, congestion, server limits, and protocol overhead mean real throughput is usually below the plan speed.
- Forgetting overhead. Estimates are for the payload; real transfers carry some extra data.
Common files at 100 Mbps
| File | Size | Download time |
|---|---|---|
| Photo | 5 MB | 0.4 s |
| Song (high bitrate) | 10 MB | 0.8 s |
| Podcast episode | 50 MB | 4 s |
| SD movie | 700 MB | 56 s |
| HD movie | 4 GB | 5m 20s |
| Large game | 60 GB | 1h 20m |
Small files are effectively instant on a fast line, which is why the difference between 100 Mbps and 1 Gbps is only visible on large downloads and updates. The same maths covers uploads — just enter your upload speed, which is usually far lower than download.
Frequently asked questions
Why does 50 Mbps download slower than 50 MB/s?
Because the units differ by a factor of eight. 50 Mbps is 50 million bits per second, which is 6.25 million bytes per second. A 750 MB file therefore takes about two minutes, not fifteen seconds.
Is a kilobyte 1,000 or 1,024 bytes?
Both conventions exist. This calculator uses decimal (1,000); storage and memory often use binary (1,024). The number base converter shows why 1,024 — a power of two — sits naturally in digital systems.
Why is my real speed lower than the plan?
Wi-Fi interference, network congestion, the speed of the server you are downloading from, and protocol overhead all reduce throughput. A speed test measures a clear line at a good moment; a large download at peak time often runs well below it. Treat the estimate as a best case and allow extra time for anything important.
Does upload speed matter?
Yes, and it is usually much lower than download speed on home connections. Swap in your upload figure to estimate how long sending the same file will take.