Bandwidth Calculator
Enter a file size and connection speed to find the download or upload time. Switch modes to reverse-solve for required speed or to estimate how much data a connection carries in a given period. The website bandwidth mode helps you plan server capacity from page views and page size. All units covered: bits and bytes, kbps through Gbps.
Formula
Worked example
A 700 MB file over a 100 Mbps connection: 700 MB x 8 = 5600 Mb = 5,600,000,000 bits. Speed = 100,000,000 bps. Time = 5,600,000,000 / 100,000,000 = 56 seconds.
How to use this calculator
Select a mode from the "Calculate" dropdown. For "Download / upload time" enter your file size and connection speed. For "Required speed" enter the file size and the maximum time you can afford, and the calculator finds the minimum connection speed. For "Data volume" enter the connection speed and a duration to see how much data moves. For "Website bandwidth" enter your expected page views, average page size and a redundancy factor (1.5 is a common safe margin), and the calculator returns the sustained bandwidth and monthly data transfer you need to plan for.
The bandwidth formula
Bandwidth is the rate at which data moves, measured in bits per second (bps) and its multiples: kbps, Mbps, Gbps. The core relationship is simple: Transfer time = File size (in bits) / Speed (in bps). Because file sizes are often quoted in bytes and speeds in bits, the most common mistake is forgetting the 8x factor. One byte = 8 bits, so a 100 MB file is 800 megabits. A 100 Mbps connection delivers 12.5 megabytes per second, not 100. This calculator handles all unit conversions automatically.
Bits vs. bytes: why the confusion matters
Internet speeds are advertised in megabits per second (Mbps) while file sizes are shown in megabytes (MB). The lowercase b in Mbps means bits; the uppercase B in MB means bytes. Because 1 byte = 8 bits, a 1 Gbps fibre connection delivers 125 megabytes per second. When you see "1 Gbps" advertised, you can actually transfer 1000 / 8 = 125 MB every second under ideal conditions. Real-world speeds are usually 70-90% of the rated figure due to TCP/IP overhead, routing latency and network contention.
Website bandwidth planning
For web servers and hosting plans, bandwidth is typically quoted as monthly data transfer (in GB) or as a sustained line speed (in Mbps). To estimate your needs, multiply your average page views per day by the average page size, then scale to a month (30 days) and add a redundancy margin. A site getting 10,000 page views per day with a 2 MB average page size transfers about 600 GB per month. Peak traffic can be 3-5x the daily average, so a 1.5x redundancy factor on the sustained bandwidth is a conservative minimum. CDNs (content delivery networks) can offload most static asset bandwidth at a fraction of the cost of raw origin bandwidth.
Common connection types and speeds
| Connection type | Speed | Time to transfer 1 GB |
|---|---|---|
| Modem / Dialup | 56 kbps | ~33 hours |
| ADSL1 | 8 Mbps | ~17 min |
| ADSL2+ | 24 Mbps | ~5.6 min |
| 4G LTE | 100-300 Mbps | 27-82 s |
| Fast Ethernet | 100 Mbps | ~80 s |
| 5G (mid-band) | 400-3000 Mbps | 2.7-20 s |
| Gigabit Ethernet | 1 Gbps | ~8 s |
| Wi-Fi 6 (802.11ax) | up to 9.6 Gbps | < 1 s |
| 10 Gigabit Ethernet | 10 Gbps | < 1 s |
Theoretical maximum speeds. Real-world throughput is typically 70-90% of these values.
Frequently asked questions
Why is my actual download speed slower than my broadband plan speed?
Advertised speeds are the theoretical maximum of the physical link. Real throughput is reduced by TCP/IP overhead (roughly 10%), the fact that you share the connection with neighbours on a shared medium (cable, DSL), distance from the exchange or cell tower, router quality, and congestion in the ISPs backbone during peak hours. A 100 Mbps plan commonly delivers 80-95 Mbps in a speed test, but closer to 50-70 Mbps at peak evening times.
What is the difference between bandwidth and speed?
In everyday use the terms are interchangeable: both describe the maximum rate at which data can travel across a link, measured in bits per second. Strictly, bandwidth is the capacity of the channel (analogous to the width of a pipe), while speed or throughput is what you actually achieve. Latency (ping) is a separate concept - it is the round-trip time for a small packet and matters for gaming and video calls more than raw bandwidth does.
How long does it take to download a 1 GB file on various connections?
At 10 Mbps: about 800 seconds (13 min). At 100 Mbps: about 80 seconds. At 1 Gbps: about 8 seconds. These are theoretical; real times are 10-30% longer due to overhead.
How much bandwidth does streaming video use?
Netflix recommends 5 Mbps for HD (1080p), 15 Mbps for 4K Ultra HD, and 25 Mbps for 4K with HDR. YouTube uses roughly 5 Mbps for 1080p and 20 Mbps for 4K. A household with several simultaneous 4K streams needs 50-100 Mbps just for video.
What is a redundancy factor in website bandwidth calculations?
Web traffic is not constant. A typical site sees traffic spikes 2-5 times the daily average during events or viral moments. A redundancy factor of 1.5 means your server has 50% headroom above the average sustained load. Most infrastructure architects use 1.5 to 2.0 for standard sites and 3.0 or more for anything likely to experience sudden viral traffic.
How do I convert Mbps to MB/s?
Divide by 8. Because there are 8 bits in a byte, 100 Mbps = 100 / 8 = 12.5 MB/s. Conversely, multiply MB/s by 8 to get Mbps. This is the single most common source of confusion in bandwidth calculations.