Download Time Calculator
How long will that download take? Enter the file size and your connection speed. The calculator handles the classic trap — internet speeds are in bits, file sizes in bytes, a factor of 8 that makes downloads feel slower than the marketing promised.
How to use this calculator
- Enter the file size and its unit (MB, GB, TB).
- Enter your connection speed — usually Mbps from your plan.
- Press Calculate. The 70%-efficiency row is closer to real-world experience than the theoretical time.
Formula used
The whole trick is unit consistency: ISPs advertise megabits per second (Mbps), files are measured in megabytes (MB), and 1 byte = 8 bits. So a 100 Mbps connection moves at most 12.5 MB/s — divide the advertised number by 8 to get real download speed.
Example calculation
A 5 GB file on a 100 Mbps connection: 5 GB = 40,000 megabits ÷ 100 = 400 seconds ≈ 6.7 minutes in theory.
At a realistic 70% efficiency, expect closer to 9.5 minutes — the gap between the marketed speed and lived experience.
Bits, bytes, and why downloads disappoint
The single most common confusion in networking: your "100 Mbps" plan is 100 megabits per second, but files are sized in bytes, and a byte is 8 bits. Divide by 8 and that 100 Mbps is really 12.5 MB/s at best — which is why a download that "should" be instant takes minutes.
Then reality shaves more off: protocol overhead, distant or throttled servers, Wi-Fi interference and shared bandwidth typically deliver 60–80% of the theoretical rate. The calculator shows both the ideal and the realistic figure so the estimate matches what you'll actually watch on the progress bar.
Why use this calculator?
- Estimate downloads, uploads and backups before committing to them.
- Stop being fooled by the bits-vs-bytes factor of 8.
- Get a realistic time, not just the theoretical best case.
Frequently asked questions
Why is my download speed 8 times slower than my plan?
It isn't — you're comparing bits to bytes. A 100 Mbps (megabit) plan delivers about 12.5 MB/s (megabytes), because 1 byte = 8 bits. Download managers show MB/s while ISPs advertise Mbps.
How long to download a 1 GB file?
On 100 Mbps, about 80 seconds in theory (~2 minutes realistically); on 1 Gbps, roughly 8 seconds; on 10 Mbps, around 13 minutes. Enter your exact numbers above.
Why don't I get my full advertised speed?
Overhead (TCP/IP framing), server-side limits, Wi-Fi vs wired connection, network congestion and distance to the server all reduce throughput. Getting 60–80% of the rated speed is normal; wired connections to fast servers do best.