Download Time Calculator
Estimate file download time from its size and your connection speed. Compare the theoretical minimum with an adjustable real-world transfer estimate.
Theoretical transfer time
Decimal units: 1 GB = 1,000 MB; 1 byte = 8 bits. The theoretical time uses the full entered speed. The estimate uses your usable-speed percentage; neither includes installation time.
Compare connection speeds
Same file size at 85% sustained throughput. Installation and server waiting time are excluded.
| Connection speed | Estimated transfer time |
|---|---|
| 100 Mbps | 2h 36m 52s |
| 300 Mbps | 52m 18s |
| 600 Mbps | 26m 9s |
| 1000 Mbps | 15m 42s |
Formula checked · NumberSwift · Review process
How long does it take to download 100 GB?
Decimal 100 GB at a constant speed. The comparison assumes 85% usable throughput; server limits, Wi-Fi and installation can add time.
| Connection speed | Theoretical transfer time | Real-world estimate |
|---|---|---|
| 25 Mbps | 8h 53m 20s | 10h 27m 28s |
| 50 Mbps | 4h 26m 40s | 5h 13m 44s |
| 100 Mbps | 2h 13m 20s | 2h 36m 52s |
| 300 Mbps | 44m 27s | 52m 18s |
| 500 Mbps | 26m 40s | 31m 23s |
| 1000 Mbps | 13m 20s | 15m 42s |
How this calculator works
File size and connection speed use different units. Convert the file from bytes to bits, then divide by bits per second. A connection advertised at 300 Mbps can theoretically carry 37.5 MB each second. The real-world estimate allows for reduced sustained throughput; it is a planning scenario rather than a measured prediction.
Formula
seconds = size in bytes × 8 / bits per second
Assumptions & limitations
Decimal units: 1 GB = 1,000 MB; 1 byte = 8 bits. The theoretical time uses the full entered speed. The estimate uses your usable-speed percentage; neither includes installation time.
Sources & reference material
- NIST: binary prefixes and bits/bytes ↗
Reference for unit definitions; not a validation of actual transfer speed.
Worked example
A 100 GB file contains 800,000 megabits. At 300 Mbps, 800,000 ÷ 300 = 2,666.67 seconds: 44 minutes 27 seconds. At 85% usable speed (255 Mbps), the estimate is 52 minutes 17 seconds. Server waiting time is not included.
If your download app reports MB/s, use the Mbps to MB/s Converter to enter the same transfer rate in Mbps.
Our approach to calculations ↗Common questions
Does 1 GB mean 1,000 MB or 1,024 MB?
This tool uses decimal GB: 1 GB is 1,000 MB. If a program reports GiB, convert that binary size before entering it.
Why is my real download slower?
Server limits, Wi-Fi, congestion and simultaneous transfers affect sustained speed. Adjust usable connection speed to compare assumptions; the default 85% is not a measured guarantee.
How do I use a speed reported in MB/s?
Multiply MB/s by eight to obtain Mbps, or use the Mbps to MB/s converter below.