Why is my real download slower than the calculation?

Server limits, Wi-Fi retransmissions and other traffic share the link; the calculation assumes you get the full rate.

Does the calculator include disk write speed?

No, it only models the network transfer.

Network calculators

Enter file size and connection speed to get the real transfer time in seconds.

seconds = sizeMB × 8 × (1 + overhead/100) ÷ speedMbps

8 bits = 1 byte, so the megabyte size is multiplied by eight before dividing by the megabit rate.
Real throughput is lower than advertised: TCP, encryption and Wi-Fi overhead typically eat 5–15 %.

File size(MB)

Connection speed(Mbit/s)

Protocol overhead(%)

353.9

5 min 54 s

Formula: seconds = sizeMB × 8 × (1 + overhead/100) ÷ speedMbps
Example: File size: 4096 MB Speed: 100 Mbit/s Overhead: 8 % Result: ~354.9 s (5 min 55 s)

Example

File size: 4096 MB
Speed: 100 Mbit/s
Overhead: 8 %
Result: ~354.9 s (5 min 55 s)

Why is my real download slower than the calculation?: Server limits, Wi-Fi retransmissions and other traffic share the link; the calculation assumes you get the full rate.
Does the calculator include disk write speed?: No, it only models the network transfer.

Copies: 9,820 · Views: 21,330 · Updated: Sep 17, 2026

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