Bandwidth & Download Speed Calculator
Estimate how long a file takes to download at a given internet speed, and how quickly a monthly data cap runs out. Enter the file size in GB, your connection speed in Mbps, and your monthly data allowance, and the calculator returns the download time and how many days of continuous use your cap allows.
Formula
Download Time (s) = File Size (MB) × 8 / Speed (Mbps)
Days for Monthly Cap = Monthly GB × 8000 / Speed (Mbps) / 86400
- Speeds are quoted in megabits per second (Mbps) but file sizes are in megabytes (MB), so the size is multiplied by 8 to convert bytes to bits.
- Download time = file size in megabits ÷ connection speed in Mbps.
- Real-world speeds are usually lower than the advertised rate because of overhead, Wi-Fi, and network congestion, so treat the time as a best case.
- This uses 1 GB = 1000 MB (the decimal convention internet providers use), not 1024.
4 GB file at 50 Mbps, 100 GB monthly cap
Inputs
- File Size: 4 GB
- Download Speed: 50 Mbps
- Monthly Data Cap: 100 GB
4 GB = 4,000 MB = 32,000 megabits. At 50 Mbps that's 32,000 ÷ 50 = 640 seconds ≈ 10.7 minutes. A 100 GB cap at full speed would last about 4.6 days of continuous downloading.
Frequently asked questions
Why is download time longer than I expect?
Internet speeds are measured in megabits (Mbps) while files are in megabytes (MB), and 1 byte is 8 bits. Real speeds are also reduced by network overhead and Wi-Fi, so actual downloads are slower than the headline rate.
What's the difference between Mbps and MBps?
Mbps is megabits per second (how connections are advertised); MBps is megabytes per second (how file managers often show progress). Divide Mbps by 8 to get MBps.
How do I work out download time?
Multiply the file size in MB by 8 to get megabits, then divide by your speed in Mbps. This calculator does that conversion for you.
How long will my data cap last?
It depends on your usage rate. The calculator shows how many days of continuous downloading at your speed it would take to use the whole cap — normal browsing and streaming use far less.