What the Download Time Calculator does
This calculator estimates how long a file takes to download or upload at your connection speed - a 100 GB game, a 4K film, a phone backup, a work folder. Enter the size and the speed and it gives the time, the real transfer rate in MB/s and a table of the same transfer across common broadband speeds.
It sorts out the two things that make download times confusing: speeds are sold in megabits while files are measured in megabytes (8 bits to a byte), and some software counts a gigabyte as 1,000,000,000 bytes while Windows counts 1,073,741,824. A realistic efficiency setting allows for the overhead every connection loses.
How to use it
- Enter the file size and pick its unit. Game stores, phone makers and drive labels use decimal GB; Windows Explorer shows binary sizes (it says GB but means GiB), so choose GiB if you are reading the number from Windows.
- Enter the connection speed. Broadband and mobile plans are quoted in Mbps; a download manager or Steam may show MB/s instead - pick whichever you are reading. For uploads, use your upload speed, which is often much lower.
- Leave efficiency at 90% for a good wired connection, lower it to 60-80% for busy Wi-Fi or a distant server, or set 100% to see the theoretical best.
- Read the time in the big panel, the real speed in MB/s and the comparison table, and copy or download the result.
Reading the results
Divide a speed in Mbps by 8 to get megabytes per second: 100 Mbps is 12.5 MB/s at most, and about 11.25 MB/s at 90% efficiency. That single conversion explains most "why is my download so slow" surprises.
Efficiency covers protocol overhead and real-world losses. On Ethernet with standard 1500-byte packets, TCP/IP headers and framing alone leave at most 94.9% of the line for your data; Wi-Fi interference, other devices on the same connection, VPNs and the server's own limits take more. Your provider's advertised speed is also usually a best case.
The result is an estimate of a steady transfer. Real downloads often start slowly, vary through the day and may be capped by the server or game store; run a speed test to check what you actually get and type that in.
Worked example: a 100 GB game on a 100 Mbps line
100 GB is 100 x 10^9 x 8 = 800,000,000,000 bits. At 100 Mbps and 90% efficiency the file moves at 90,000,000 bits a second, so it takes 800,000,000,000 / 90,000,000 = 8,889 seconds - about 2 hours 28 minutes.
If Windows shows the folder as "100 GB", it is really 100 GiB = 107.4 GB, and the same download takes about 2 hours 39 minutes. On a 500 Mbps line it falls to about 30 minutes, which the table shows without retyping anything.
Formulas and scoring rules
- Transfer time
time (s) = size in bytes x 8 / (speed in bit/s x efficiency / 100)- Units
1 Mbps = 1,000,000 bit/s; 1 MB = 1,000,000 bytes; 1 MiB = 1,048,576 bytes; 1 GiB = 1,073,741,824 bytesDecimal and binary prefixes as defined in IEC 80000-13. A speed in MB/s is multiplied by 8,000,000 to get bit/s.- Best-case protocol efficiency
1460 / 1538 = 94.9%1500-byte Ethernet frames: 1460 bytes of TCP payload out of 1538 bytes on the wire (20-byte IPv4 and 20-byte TCP headers, 14-byte Ethernet header, 4-byte checksum, 8-byte preamble and 12-byte gap).
Limitations: what the result does not prove
- It does not measure your connection. Use a speed test, and remember results vary with time of day, Wi-Fi signal and the server you download from.
- Game stores and cloud services often compress downloads and then unpack them, so the download can be smaller than the installed size and installation adds time after the download ends.
- Several downloads at once share the connection; the time shown is for one transfer using all of it.
- Mobile data speeds change from minute to minute; treat a mobile estimate as a rough guide.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- IEC 80000-13 - Information science and technology quantities (KiB, MiB) - checked 19 Sep 2026
- NIST - Prefixes for binary multiples
- IETF RFC 9293 - Transmission Control Protocol (TCP)
Frequently asked questions
How long does it take to download 1 GB at 100 Mbps?
About 80 seconds at the full line rate, or about 89 seconds at a realistic 90% efficiency. 1 GB is 8,000 megabits, and 8,000 / 100 = 80 seconds.
What is the difference between Mbps and MB/s?
Mbps is megabits per second, the unit broadband is sold in; MB/s is megabytes per second, the unit many download managers show. One byte is 8 bits, so divide Mbps by 8: a 200 Mbps plan delivers at most 25 MB/s.
Why is my download slower than my internet speed?
Part of every connection goes on protocol overhead (about 5% on wired Ethernet), and Wi-Fi, other devices, the server's own limit and evening congestion take more. A sold speed is usually a maximum, so 70-90% of it is a normal real-world result.
How long will a 100 GB game take to download?
About 2.5 hours at 100 Mbps, 1 hour 15 minutes at 200 Mbps, 30 minutes at 500 Mbps and 15 minutes at 1 Gbps, all at 90% efficiency. Enter your own speed for your figure.
Why does Windows show a different size from the game store?
Stores use decimal gigabytes (10^9 bytes) and Windows uses binary ones (2^30 bytes) while still writing GB. The same file is 100 GB in the store and about 93 GB in Windows; choose the unit that matches where you read the number.
How do I calculate upload time for a backup?
Use the same formula with your upload speed, which on many home plans is a fraction of the download speed. A 64 GB phone backup at 20 Mbps upload and 85% efficiency takes about 8 hours 21 minutes.
What does the efficiency setting mean?
It is the share of your connection speed that actually carries file data. 90% is a fair figure for a good wired connection; set it lower for crowded Wi-Fi or a slow server, or to 100% to see the theoretical minimum time.
Last reviewed by the A2Z.Tools team against the sources listed above.
