Bandwidth Calculator - Download Time, Speed & File Size
Enter any two of file size, connection speed, and transfer time to instantly solve for the third. Switch modes to calculate required bandwidth for a target download window, or estimate how much bandwidth your website needs based on daily page views. All common units are supported, from bps to Gbps and bytes to terabytes.
What is bandwidth?
Bandwidth is the maximum rate at which data can travel across a network link, measured in bits per second (bps). Think of it as the width of a pipe: a wider pipe can carry more water at once, just as a higher-bandwidth connection can carry more data. Common units are kilobits per second (Kbps), megabits per second (Mbps), and gigabits per second (Gbps). Note that internet speeds are quoted in megabits, while file sizes are usually shown in megabytes: there are 8 bits in 1 byte, so a 100 Mbps connection can transfer roughly 12.5 MB of data every second.
How to calculate download time
The core formula is straightforward: Transfer Time (seconds) = File Size (bits) / Speed (bps). To apply it, first convert your file size to bits by multiplying the byte count by 8. Then convert your speed to bits per second (a 50 Mbps connection is 50,000,000 bps). Dividing gives the theoretical minimum time. In practice, expect 10-20% overhead from TCP/IP protocol headers, TLS encryption, and retransmission of lost packets, so real-world times will be slightly longer. This calculator uses the raw formula; for a practical estimate, add about 15% to the result.
Reverse calculations: finding required speed or file size
The same formula rearranges to solve for any of its three variables. If you need to download a 50 GB file within 1 hour, rearrange to Required Speed = File Size (bits) / Time (seconds): that is 50 x 1024 x 1024 x 1024 x 8 / 3600 = approximately 111 Mbps. If you know your speed and how long you have, you can also calculate the maximum file size you can transfer in that window: File Size (bits) = Speed (bps) x Time (seconds). Use the mode selector above to access all three variations.
Website bandwidth requirements
A website's bandwidth need depends on page views and average page size. Monthly Data = Page Views x Average Page Size. For example, 50,000 page views per month at 2 MB per page = 100 GB per month of data delivered to visitors. Dividing by the seconds in a month and multiplying by 8 gives the average continuous bandwidth in bps. A redundancy factor of 1.5-3 accounts for traffic spikes: if your busiest hour draws 5x the average traffic, your hosting plan must handle that peak rather than just the monthly mean. Most hosting providers quote a monthly data allowance rather than a bandwidth cap, so compare your monthly GB figure against that allowance.
Common internet connection speeds
| Connection type | Typical download speed | Notes |
|---|---|---|
| Dialup modem | 56 kbps | Obsolete; still used in remote areas |
| ADSL / DSL | 1-25 Mbps | Speed declines with distance from exchange |
| Cable broadband | 25-500 Mbps | Shared neighbourhood capacity |
| Fiber (FTTP) | 100-10,000 Mbps | Fastest residential option |
| Wi-Fi 802.11n (2.4/5 GHz) | Up to 300 Mbps | Practical range 50-150 Mbps indoors |
| Wi-Fi 6 (802.11ax) | Up to 9,600 Mbps | Practical 500-1,500 Mbps on modern hardware |
| 3G mobile | 1-10 Mbps | Widely supported fallback network |
| 4G LTE | 10-150 Mbps | Typical average 20-50 Mbps in urban areas |
| 5G (mid-band) | 100-900 Mbps | Best urban coverage; sub-6 GHz band |
| 5G (mmWave) | 1,000-3,000 Mbps | Dense urban only; short range |
| Gigabit Ethernet | 1,000 Mbps | Standard wired LAN backbone |
| 10 Gigabit Ethernet | 10,000 Mbps | Data-centre and high-end NAS connections |
Typical real-world throughput for common technologies. Actual speeds vary by provider and location.
Frequently asked questions
Why is my actual download speed slower than my plan speed?
Your stated plan speed is a theoretical ceiling, not a guarantee. Real-world throughput is reduced by TCP/IP and TLS protocol overhead (roughly 5-10%), congestion on your local network or the ISP backbone during peak hours, Wi-Fi interference and signal loss, and the speed of the remote server you are downloading from. A 100 Mbps plan typically delivers 80-95 Mbps on a wired connection and somewhat less over Wi-Fi. Run a speed test at fast.com or speedtest.net to measure your actual current throughput.
What is the difference between Mbps and MBps?
Mbps (megabits per second) and MBps (megabytes per second) differ by a factor of 8, because there are 8 bits in 1 byte. Internet providers advertise speeds in Mbps, while file sizes and download managers typically show progress in MB or MBps. A 100 Mbps connection transfers 12.5 MB of data per second. When comparing your plan speed with download progress, divide the Mbps figure by 8 to get the equivalent in MBps.
How much bandwidth does streaming video use?
Video streaming bitrates vary by quality. Standard definition (480p) requires about 3 Mbps, HD (1080p) needs 5-8 Mbps, 4K Ultra HD needs 15-25 Mbps, and 4K HDR streams from services like Netflix or Apple TV+ can reach 40 Mbps. These are sustained bandwidth requirements, so if multiple people in your household stream simultaneously, add the individual requirements together to estimate your peak household need.
What is the redundancy factor in the website bandwidth calculator?
The redundancy factor accounts for traffic peaks above your monthly average. If your site has a product launch or a news spike, traffic can be 3-10 times the usual hourly rate. A redundancy factor of 1.5 adds a 50% buffer above the flat monthly average, meaning your hosting or CDN needs to handle that headroom without slowing down. A factor of 2 is common for most sites; high-traffic or viral-prone content should use 3 or higher.
How long does it take to download 1 GB?
At common connection speeds: on dialup (56 kbps), a 1 GB download would take over 35 hours. On a 10 Mbps DSL line, about 14 minutes. On a 100 Mbps cable or fiber connection, about 1.3 minutes. On a 1 Gbps fiber line, around 8 seconds. On a 10 Gbps enterprise link, under 1 second. Use the calculator above with 1 GB and your actual speed to get a precise figure.