Enter any two of file size, transfer speed, and time to solve for the third.
How to Use the Bandwidth Calculator
Pick a mode — Find Time, Find Speed, or Find Size — then fill in the two fields that stay editable; the third is calculated and grayed out. Each field has its own unit dropdown, so a 500 MB file at 100 Mbps doesn't need converting by hand first.
The single most common mistake in any bandwidth math is mixing up bits and bytes. File sizes are measured in bytes — a MB is a megabyte. Internet speeds are almost always advertised in bits per second — a Mbps is a megabit. One byte equals eight bits, so a connection rated at 8 Mbps moves roughly 1 megabyte per second, not 8.
An 8 MB File Doesn't Take 1 Second Over an 8 Mbps Line
Here's the trap in numbers: an 8 MB file over an 8 Mbps connection takes about 8 seconds, not 1. The file is 8 megabytes, which is 64 megabits, and 64 megabits divided by an 8-megabit-per-second connection is 8 seconds. Read the units and the "8 = 8" coincidence disappears.
8 MB × 8 = 64 megabits
64 megabits ÷ 8 Mbps = 8 secondsThis calculator converts everything to bits and seconds internally before doing any math, then converts back to whatever unit you picked for display — the bits-vs-bytes gap is handled for you rather than something to remember mid-calculation.
Decimal Units, Not Binary
File size units here use decimal (SI) prefixes — 1 MB = 1000 KB, 1 GB = 1000 MB — matching how ISPs and speed tests report numbers, rather than the binary 1024-based prefixes your operating system's file browser sometimes uses. That mismatch is a second, smaller source of "why don't these numbers match" confusion, even though it's not the main one.
Anyone estimating a backup window, a video upload, or how long a large game download will take is really doing this same three-variable relationship in their head — this just handles the unit conversion cleanly.