SuperDevTools
EN

Download time calculator and bandwidth calculator

The tool works from the speed you enter: it does not measure your connection. Everything is calculated in your browser.

Usable speed is lower than the advertised speed: network protocol headers, Wi-Fi and distance from the router, a slower remote server, other devices sharing the line. 90% suits a healthy wired connection; try 50 to 70% on Wi-Fi.

Find
Direction
File size result
kB, MB, GB, TB: multiples of 1,000 (1 GB = 1,000,000,000 bytes). KiB, MiB, GiB, TiB: multiples of 1,024 (1 GiB = 1,073,741,824 bytes), the unit some operating systems show under the name "GB".
Download speed result
Time result
Working

    Your last values stay in this browser.

    How long will this file take to download?

    This download time calculator links three values: file size, connection speed and time. Enter any two and it gives you the third, with the working shown, so it doubles as a bandwidth calculator when you need to know what speed a job requires. It also converts Mbps to MB/s, shows a table of examples and estimates the data used by streaming. One thing to know up front: it does not test your connection. It calculates from the speed you type in, and everything runs in your browser.

    How to use it

    1. Set "Real-world efficiency (%)": 90% by default, or pick a button from 100% down to 50%.
    2. On the "Time and speed" tab, choose after "Find": "the time", "the speed" or "the size". The box being worked out is marked "result".
    3. Pick a "Direction": "Download" uses the "Download speed", "Upload" uses the "Upload speed", which the tool keeps separately.
    4. Fill in the other two boxes. Time is entered in days, hours, minutes and seconds, and the answer comes back in the same form.
    5. "Copy link" creates an address that reopens the calculation with your values.

    Bits and bytes: the factor of 8

    One byte is 8 bits. Internet plans quote speeds in megabits per second (Mbps or Mbit/s), while files and download managers use megabytes (MB). A small "b" means bit, a capital "B" means byte. To go from Mbps to MB/s, divide by 8: 100 Mbps is 12.5 MB/s. The "Mbps ↔ MB/s" tab converts both ways.

    GB or GiB: decimal and binary prefixes

    kB, MB, GB and TB are multiples of 1,000: 1 GB = 1,000,000,000 bytes. KiB, MiB, GiB and TiB are multiples of 1,024: 1 GiB = 1,073,741,824 bytes. Some operating systems show GiB but label them "GB", which is why a drive sold as 1 TB appears as about 931 GiB (0.91 TiB).

    Formula and worked examples

    time (s) = size in bytes × 8 ÷ (speed in bit/s × efficiency)

    CalculationResult
    4 GB at 100 Mbps, 100%32,000,000,000 ÷ 100,000,000 = 320 s, i.e. 5 min 20 s
    4 GiB at 100 Mbps, 100%343.6 s
    4 GB at 100 Mbps, 90%355.6 s, i.e. 5 min 56 s
    1 TB at 1 Gbps, 100%8,000 s, i.e. 2 h 13 min 20 s
    10 GB in 10 minutes133.3 Mbps usable, 148.1 Mbps advertised at 90%

    The "Examples" tab runs the same sum for four typical files and five example speeds, from 8 Mbps to 8 Gbps.

    Why real speed is lower than advertised

    An advertised speed is a ceiling. Part of every packet carries network protocol headers, Wi-Fi loses a lot through walls and distance, and the server on the other end may be slower than your line. Hence the efficiency setting: 90% for a healthy Ethernet cable, often less on Wi-Fi.

    Download and upload

    Upload speed is often much lower than download speed, especially on cable, DSL and mobile networks. Sending a 20 GB backup to the cloud over a 20 Mbps upload at 90% takes 8,888.9 s, or 2 h 28 min 9 s.

    Streaming data use

    The "Streaming" tab multiplies a stream's bitrate by its duration: 5 Mbps for 2 hours is 5 × 7,200 ÷ 8 = 4,500 MB, or 4.5 GB, which is 2.25 GB per hour. As a rough guide, standard definition video often runs at around 1 to 3 Mbps, HD at around 5 Mbps and 4K between 15 and 25 Mbps, while music needs only a few hundred kbps. Actual figures vary by service and quality setting.

    FAQ

    Does this tool measure my internet speed?

    No. It runs no speed test: it calculates from the value you enter. Run a speed test first if you want your real figure, then type it in here.

    Why does my download show 12 MB/s on a 100 Mbps plan?

    That is expected: 100 Mbps ÷ 8 = 12.5 MB/s at most. The software counts bytes, the plan counts bits.

    Should I pick GB or GiB?

    Use the unit shown next to the file. If unsure, the gap is small for a time estimate: 4 GiB is 4.29 GB, 7.4% more.

    What efficiency should I enter?

    90% is a sensible starting point on a wired connection. If your speed test already gives the real speed, set 100% so losses are not counted twice.