Data Transfer Speed Calculator
Connection speeds are advertised in megabits per second while files are measured in megabytes, and the factor of eight between bits and bytes trips many people up. This calculator converts your file size to bits, divides by your connection speed, and applies an efficiency fraction for real-world overhead to estimate how long a download or upload will take. It returns the time in seconds and minutes and the effective throughput, so you can plan transfers and judge whether a connection is fast enough.
Data transfer formula
File megabits = file MB * 8
Effective speed (Mbps) = connection speed * efficiency / 100
Transfer time (seconds) = file megabits / effective speed
Transfer time (minutes) = transfer seconds / 60
One byte is eight bits, so a megabyte is eight megabits. Dividing the file in megabits by the effective speed in megabits per second gives the time in seconds. The efficiency fraction accounts for overhead so the estimate matches reality.
Data and bandwidth context
- The SI prefix mega means one million; ISPs advertise speeds in decimal megabits per second.
- One byte equals eight bits, so an 8 Mbps line moves at most 1 MB per second.
- Real throughput is reduced by protocol overhead, congestion and Wi-Fi loss.
- The FCC defines US broadband as at least 100 Mbps download and 20 Mbps upload.
- Upload is often slower than download on consumer connections; enter the relevant speed.
Data transfer: frequently asked questions
How do I convert Mbps to download time?
Internet speed is in megabits per second (Mbps), but file size is in megabytes (MB). One byte is 8 bits, so first convert the file to megabits (MB times 8), then divide by the speed in Mbps to get seconds. A 1,000 MB file on a 100 Mbps line takes 1,000 * 8 / 100 = 80 seconds at full speed.
Why is my real download slower than this?
Protocol overhead, congestion, server limits and Wi-Fi loss mean you rarely get the full advertised speed. Set the efficiency input below 100 percent (often 80 to 90 percent) to model effective throughput. The calculator divides by that fraction to give a realistic time.
What is the difference between MB and Mb?
A capital B means bytes; a lowercase b means bits. File sizes are quoted in megabytes (MB); connection speeds in megabits per second (Mbps). Because 1 byte equals 8 bits, an 800 Mbps connection moves 100 MB per second at best.
Does the calculator use 1000 or 1024?
Networking and storage marketing use decimal units, where 1 megabyte equals 1,000,000 bytes and 1 megabit equals 1,000,000 bits, as defined by the International System of Units. This calculator uses the decimal convention, matching how ISPs advertise speeds.
How is effective speed reported?
Effective speed is the advertised speed multiplied by the efficiency fraction. At 100 Mbps and 90 percent efficiency, effective speed is 90 Mbps, and download time is based on that figure. This makes the estimate closer to what you actually observe.
Official sources
- U.S. Federal Communications Commission: Broadband Speed Guide.
- National Institute of Standards and Technology: SI Prefixes.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.