Free Bandwidth Calculator - File Size vs Speed in Mbps / Gbps

Bandwidth Calculator

Three ways to solve the same equation: size ÷ speed = time. Enter any two, and the calculator derives the third. Handles the common "MB vs Mbps" bits-vs-bytes trap automatically, and includes unit toggles for KB/MB/GB/TB (file size) and Kbps/Mbps/Gbps (bandwidth). Presets for common home and enterprise links.

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Transfer time8.00 s

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Bandwidth Calculator guide

How to use the Bandwidth Calculator accurately

The calculator rearranges the single relationship time = size / speed in three directions so you can solve for any missing value.

01 How The Bandwidth Calculator Works The calculator rearranges the single relationship time = size / speed in three directions so you can solve for any missing value.

02 Theoretical vs Actual Transfer Times The calculator reports ideal transfer time at 100% line efficiency. Real-world transfers lose 5-15% to TCP/IP overhead (headers, acks, slow-start), and more if the link has high round-trip latency, packet loss, or encryption.

03 Common Link Speeds And Their Real Transfer Rates For quick reference, at 100% efficiency: 25 Mbps downloads ~3 MB/s (a 4 GB game takes ~22 minutes); 100 Mbps does ~12.5 MB/s (same game in ~5.5 minutes); 300 Mbps does ~37.5 MB/s (~1.

04 Binary vs Decimal Units This calculator uses binary units: 1 KB = 1024 bytes, 1 MB = 1,048,576 bytes, matching how Windows and most file managers display sizes.

bandwidth calculator data transfer calculator mbps to mb/s file size to time upload time calculator network speed calculator

For quick reference, at 100% efficiency: 25 Mbps downloads ~3 MB/s (a 4 GB game takes ~22 minutes); 100 Mbps does ~12.5 MB/s (same game in ~5.5 minutes); 300 Mbps does ~37.5 MB/s (~1.8 minutes); 1 Gbps does ~125 MB/s (~33 seconds); 2.

Bandwidth Calculator FAQ

Common bandwidth calculator questions

Why does my 100 MB file take 8 seconds on 100 Mbps?

MB is megabytes; Mbps is megabits per second. 1 byte = 8 bits. 100 MB = 800 megabits. 800 megabits / 100 Mbps = 8 seconds. The bits-vs-bytes confusion is the #1 source of "my Internet is slow" complaints that are actually correct math.

Why is the real download slower than the calculator says?

Real transfers lose 5-15% to TCP/IP overhead, more for high-latency or lossy links. The calculator reports 100% efficient transfer. For realistic estimates, multiply by 1.15 for HTTPS, 1.3-1.5 for VPN, and 2x+ for cellular or congested Wi-Fi.

Does this handle KB vs KiB correctly?

The calculator uses binary KB (1 KB = 1024 bytes) because that is what Windows and most file managers display. If you need strict decimal (1 KB = 1000), the number will be off by ~2.4% per power of 1000 - noticeable only at TB scale.

Why don't LAN transfers match the calculator on gigabit?

They often do, actually. Modern NICs and SMB drivers routinely hit 95-98% of gigabit line rate on a wired local network. If you are seeing much less, the bottleneck is disk speed (a slow 5400-rpm HDD cannot feed gigabit) or a cheap switch dropping to 100 Mbps on one port.

Checklist

Utility checks to confirm

How The Bandwidth Calculator Works The calculator rearranges the single relationship time = size / speed in three directions so you can solve for any missing value.
Theoretical vs Actual Transfer Times The calculator reports ideal transfer time at 100% line efficiency. Real-world transfers lose 5-15% to TCP/IP overhead (headers, acks, slow-start), and more if the link has high...
Common Link Speeds And Their Real Transfer Rates For quick reference, at 100% efficiency: 25 Mbps downloads ~3 MB/s (a 4 GB game takes ~22 minutes); 100 Mbps does ~12.5 MB/s (same game in ~5.5 minutes); 300 Mbps does ~37.