Download time calculator

How long will your download take?

Enter the file size and your connection speed to see how long a download or upload takes.

File size

Size unit

Connection speed

Speed unit

Real-world speed

Overhead

Download time

2 minutes, 40 seconds

2 GB at 100 Mbit/s takes about 2 minutes, 40 seconds

Behind the time

Speed after overhead: 12.5 MB/s
Total time in seconds: 160 s

What this means

Packet headers alone take at least 2.7% of every full-size packet, so real downloads run a little slower than the line speed.

How to use

Type the file size and pick its unit, such as 2 GB.
Type your connection speed and pick its unit. Providers quote Mbit/s; download programs often show MB/s.
Optionally set a percentage for overhead to see a more realistic time.

Download time for 1 GB with no overhead

Speed (Mbit/s)	Time (seconds)
10	800
25	320
50	160
100	80
500	16
1,000	8

How it works

A download takes the amount of data divided by how much your connection moves per second. The catch is the units: files are measured in bytes, but connections are quoted in bits per second. A byte is 8 bits, so a 100 Mbit/s line moves at most 12.5 megabytes each second.

time = size ÷ (speed × (1 − overhead)). For example, a 2 GB film at 100 Mbit/s is 2 GB ÷ 12.5 MB/s = 160 seconds, about 2 min 40 s. Prefixes like GB mean 1,000-based units and GiB 1,024-based units (IEC 80000-13), which is why a GiB file takes about 7 % longer than a GB file.

Real downloads are slower than the line speed. Each full-size packet on Ethernet carries at most 1,500 bytes, of which 40 are the IP and TCP headers (RFC 894, RFC 9293), so headers alone cost at least 2.7 %. Wi-Fi, encryption, a busy server or a shared line cost more, and that varies too much for one figure, so use the overhead box if you know yours.

Frequently asked questions

Why is my download slower than my advertised speed?

Advertised speeds are bits per second on the line. Headers, encryption, Wi-Fi, a busy server and other devices on your network all take a share. Test your real speed and use that.

How do I convert Mbit/s to MB/s?

Divide by 8. 100 Mbit/s is 12.5 MB/s. A lowercase b means bits and an uppercase B means bytes.

Is it the same for uploads?

Yes, the maths is identical. Use your upload speed, which is often much lower than the download speed.

What is the difference between GB and GiB?

A gigabyte is 1,000,000,000 bytes and a gibibyte is 1,073,741,824 bytes. Drive makers and providers use GB; some operating systems show GiB.

Does this measure my internet speed?

No. It estimates transfer time from the speed you enter. Use a measured speed for a more useful estimate.

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