Data Transfer Calculator
Calculate how long a file transfer will take, how large a file a transfer will produce, or what speed a transfer averaged - handling both bit-based (Mbps) and byte-based (MB/s) units correctly.
Recommended Settings
Pro Tips
- •Internet speeds are almost always advertised in bits per second (Mbps), but file sizes are shown in bytes (MB) - divide a Mbps speed by 8 to get roughly MB/s
- •A '100 Mbps' connection downloads at about 12.5 MB/s in ideal conditions, not 100 MB/s - that mismatch is the most common source of transfer-time confusion
- •Real-world transfer speeds are usually lower than the rated maximum due to network overhead, so treat the result here as a best case
- •Use the Find Speed tab after a transfer finishes to see what your connection actually averaged, in both bit and byte form
Most Popular
Most people use Find Time with a file size in GB and a speed in Mbps to estimate a download
When to Use This Tool
Find out roughly how long a large file, backup, or media library will take to transfer at a given speed.
Check whether a network link is fast enough to move a given amount of data within a time window.
Convert an advertised Mbps plan into the byte-based MB/s figure that actually matches file sizes.
Estimate whether a nightly backup will finish before a maintenance window closes.
How It Works
Choose whether you want to find the time, the resulting file size, or the average speed
Enter the two known values, each with its own unit - file sizes in bytes (KB-TB), speeds in either bits or bytes per second
Everything is converted to a common unit (bits) internally before the calculation, so bit-based and byte-based units are never mixed up
The result is converted back into a readable unit automatically
100% Private
Files never leave your device. All processing happens locally in your browser.
Lightning Fast
Powered by Client-side JavaScript arithmetic for optimal performance on modern browsers.
Open Source
Built with verified, open-source libraries. Fully transparent.
Frequently Asked Questions
Why is my download slower than my internet plan's advertised speed?
Advertised speeds (like '100 Mbps') are in bits per second, while file sizes and download-manager readouts are usually in bytes per second - divide the advertised Mbps by 8 to get the comparable MB/s figure. Real-world speeds are also often lower than the rated maximum due to network overhead.
What's the difference between Mbps and MB/s?
Mbps is megabits per second; MB/s is megabytes per second. Since there are 8 bits in a byte, 1 MB/s equals 8 Mbps - mixing them up is the most common cause of transfer-time miscalculations.
How do you calculate data transfer time?
Divide the file size (converted to bits) by the transfer speed (in bits per second). This tool does that conversion automatically regardless of which units you enter.
Does this account for real-world network overhead?
No - it calculates the theoretical time or size based on the exact numbers entered. Actual transfers are usually somewhat slower due to protocol overhead, other network traffic, and hardware limits.
Is my data sent to a server?
No. Every calculation happens locally in your browser using JavaScript - nothing is transmitted anywhere.