Download Time Calculator
Enter a file size and a transfer rate — Mbps or MB/s — and get the download time with the bits-vs-bytes math shown, entirely on this device.
80- 8 bits = 1 byte — 100 Mbps is 12.5 MB/s
Press ? for shortcuts
Do it offline:$ node -p '1*8e9/100e6'
How to use it
- Type the file size and pick its unit — bytes to terabytes, decimal (GB) or binary (GiB).
- Enter the rate and choose Mbps or MB/s; the page opens on a 1 GB at 100 Mbps sample.
- Read the time in plain words and as a seconds figure, split into days, hours, minutes and seconds.
- Copy the result, save a .txt, or share a permalink that reopens the inputs.
- Watch the bits-versus-bytes chip restate your rate in the other unit.
Enter a file size and a transfer rate and read how long the download takes: size divided by rate, with the bits-versus-bytes step shown. A 100 Mbps line moves 12.5 MB/s, not 100, because eight bits make one byte — miss that and your estimate is off by a factor of eight. Pick megabits or megabytes, decimal or binary units, all on this device.
How it works
Size becomes bits, rate becomes bits per second, and the time is one division. A gigabyte is 1,000,000,000 bytes, or 8,000,000,000 bits; a 100 Mbps link carries 100,000,000 bits a second, so the file needs 8,000,000,000 over 100,000,000 — exactly 80 seconds. The intermediates stay exact fractions.
Megabits and megabytes are the common mix-up. Plans sell megabits per second, files are sized in megabytes, eight bits to a byte, so 100 Mbps is 12.5 MB/s. A one-gigabyte file over 100 Mbps then takes 80 seconds — eight times the ten you would expect if the units matched.
Units come in two systems: a decimal gigabyte is 1,000,000,000 bytes, a binary gibibyte 1,073,741,824, seven percent more. So 1 GiB at 100 Mbps is 85.899 seconds against 80. Uneven divisions round to three decimals. Every figure is the ideal; real transfers run slower.
Examples
1 GB at 100 Mbps1 minute 20 secondsThe headline case: one gigabyte on a 100 Mbps line. Eight bits to the byte make that 12.5 MB/s, so 8,000,000,000 bits over 100,000,000 per second is exactly 80 seconds — one minute twenty.
700 MB at 5 MB/s2 minutes 20 secondsA rate already in megabytes needs no conversion: 700 MB at 5 MB/s is 700 over 5, so 140 seconds. As a byte rate it shows no bits chip; its twin is 40 Mbps.
100 MB at 3 MB/s33.333 secondsNot every division is clean. 100 MB at 3 MB/s is 33.333… seconds without end, so it rounds half-up to 33.333 and a chip marks it rounded.
Every example on this page is executed against the same engine that powers the tool, on every build.
Gotchas worth knowing
Bits versus bytes: the ÷8 trap
A byte is eight bits, so a bit rate divides by eight for its byte rate: 100 Mbps is 12.5 MB/s, 1 Gbps is 0.125 GB/s, a 500 MB/s drive is 4,000 Mbps. The lowercase b is bits, capital B bytes; a chip prints the twin for bit-rate entries.
Decimal GB and binary GiB differ
A gigabyte is 1,000,000,000 bytes; a gibibyte is 1,073,741,824 — seven percent more. So 1 GiB at 100 Mbps takes 85.899 seconds against 80 for 1 GB, and a chip flags the binary choice.
A rate of zero is refused, not divided
Dividing by zero has no answer, so a zero or negative rate is refused with a plain message, not an infinity. A negative size is refused too; zero returns zero seconds.
A fraction of a second to many days
Small jobs keep the decimal — 5 MB at 100 Mbps is 0.4 seconds — and large ones break out fully: 5 TB at 50 Mbps is 9 days 6 hours 13 minutes 20 seconds.
Common errors
Transfer rate must be greater than zero — a rate of zero never finishes- A zero rate divides by zero and a negative one is meaningless, so both stop before any math. Enter a positive number.
Enter a file size as a number (for example 700 or 1.5)- The size field takes digits with at most one decimal point. A comma decimal like 1,5 is the usual culprit — retype it as 1.5.
Enter a transfer rate as a number (for example 100 or 5.5)- Same grammar as the size field: a plain number with one optional dot. Keep unit letters like Mbps out of the number — the menu carries the unit.
File size can't be negative- A file cannot be smaller than empty, so a leading minus sign is rejected. Zero is accepted and returns zero seconds.
Value has more than 30 significant digits — this calculator caps magnitudes there- Past thirty significant digits the value is refused rather than approximated. That ceiling is far beyond any real file size or connection speed.
FAQ
Why is my real download slower than this calculator says?
This is the ideal time — file size divided by raw speed. A real transfer also pays for the link ramping up, latency, competing traffic, server limits and disk writes, none modelled here. Read it as a floor for anything time-critical.
What is the difference between Mbps and MB/s?
A byte is eight bits, so dividing a megabit-per-second rate by eight gives megabytes per second. A 100 Mbps plan is really 12.5 MB/s, and a 5 MB/s copy is 40 Mbps. Speeds are quoted in bits, files sized in bytes.
Is a GB 1000 or 1024 MB here?
Both, at your choice. GB, MB and KB are decimal, where a gigabyte is 1000 megabytes; GiB, MiB and KiB are binary, where a gibibyte is 1024 mebibytes. Binary units make a file about seven percent larger, so its transfer time grows to match.
Keyboard shortcuts
- ⌘/Ctrl + Enter
- Recompute on demand; the result already updates on every valid edit.
- ⌘/Ctrl + C
- Copy the result when nothing is selected; a focused number field is left alone.
- ⌘/Ctrl + Shift + C
- Copy the result even when text is selected.
- ⌘/Ctrl + S
- Download the result as a .txt file instead of the browser's save-page dialog.
- t
- Cycle the color theme, unless a field currently has focus.
- ? or ⌘/Ctrl + /
- Open this page's keyboard-shortcut help.
- Esc
- Close the top dialog without changing the inputs.