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Bandwidth Calculator
This bandwidth calculator answers the two questions everyone asks about their internet connection: how long will this download take, and how much data will this stream use? Enter a file size and a connection speed to get the download time, or switch to data-per-hour mode and enter a bitrate to see how many gigabytes an hour of streaming, gaming, or video calls will eat. It works with kilobytes up to terabytes and kilobits up to gigabits, so it covers everything from a small photo to a full game download.
Sizes use 1 GB = 1,024 MB. Speeds are in bits per second — remember 8 bits make 1 byte, so a 100 Mbps line moves 12.5 MB per second.
How it works
Download time is plain division: file size divided by connection speed. The only catch is the units. File sizes are measured in bytes — kilobytes, megabytes, gigabytes — while connection speeds are measured in bits per second — kilobits, megabits, gigabits. There are 8 bits in every byte, so a speed of 100 Mbps moves 12.5 megabytes per second, not 100. Forgetting that factor of 8 is the most common mistake in download maths, and it makes the answer look eight times faster than it really is.
This calculator does the unit juggling for you. It converts the file size into megabits first: multiply gigabytes by 1,024 to get megabytes, then by 8 to get megabits. A 5 GB file is 5 × 1,024 × 8 = 40,960 megabits. Then it divides by the speed in megabits per second: 40,960 ÷ 100 = 409.6 seconds. The result is shown in hours, minutes, and seconds so it reads naturally — 409.6 seconds is 6 minutes 50 seconds. The breakdown table also shows the time at 50% and 90% of your advertised speed, because real connections rarely hold their full advertised speed for a whole download.
Data-per-hour mode runs the same maths in the other direction. A stream at a steady bitrate uses a fixed amount of data every second, so the data for one hour is the bitrate multiplied by 3,600 seconds and divided by 8 to turn bits into bytes. A 5 Mbps HD stream uses 5 × 3,600 ÷ 8 = 2,250 megabytes per hour, which is about 2.20 GB. A 25 Mbps 4K stream uses about 11 GB per hour, which is why a 4K habit can eat through a monthly data allowance fast: one hour of 4K a day for a month is roughly 330 GB.
A few things make real downloads slower than the calculator's ideal figure. The speed your provider advertises is a maximum, and real speeds are usually 70 to 90 percent of it when the network is busy, when you are on Wi-Fi rather than a cable, or when other devices are streaming at the same time. The server you are downloading from can also be the bottleneck: a slow server cannot fill a fast connection. That is why the breakdown table shows the time at reduced speeds — plan with the 70% figure and you will rarely be disappointed.
Worked example
You want to download a 5 GB video file on a 100 Mbps home connection and need to know whether it will finish before you leave. Here is how the calculator works it out.
Step 1: Leave the mode on Download / transfer time.
Step 2: Type 5 into the file size box and leave the unit on Gigabytes (GB).
Step 3: Type 100 into the connection speed box and leave the unit on Megabits / sec (Mbps).
Step 4: Convert the size: 5 GB is 5 × 1,024 = 5,120 MB, and 5,120 × 8 = 40,960 megabits.
Step 5: Divide by the speed: 40,960 ÷ 100 = 409.6 seconds, which is 6 minutes 50 seconds.
The tool gives exactly this result: 6 minutes 50 seconds — 5 GB at 100 Mbps. At 70% of the advertised speed the same file takes 9 minutes 45 seconds. Try the other mode too: switch to Data used per hour, enter 5 Mbps, and the tool gives 2.20 GB per hour.
FAQ
How long will it take to download a file?
Divide the file size by the connection speed, keeping the units matched. A 5 GB file is 40,960 megabits, so on a 100 Mbps connection it takes 40,960 ÷ 100 = 409.6 seconds, or about 6 minutes 50 seconds. This calculator does the unit conversion for you — just enter the size and the speed.
Why is a download slower than my advertised speed?
Because advertised speeds are a maximum, not a promise. Your real speed drops when the network is busy, when you are on Wi-Fi instead of a cable, when the server you are downloading from is slow, or when other devices are using the same connection. Expect real speeds of 70 to 90 percent of the advertised figure in normal use.
What is the difference between MB and Mbps?
MB means megabytes, a size, while Mbps means megabits per second, a speed. There are 8 bits in a byte, so a 100 Mbps connection moves 12.5 megabytes per second. Mixing the two up is the most common mistake in download maths, and it makes the answer eight times too fast.
How much data does streaming use per hour?
Multiply the bitrate in Mbps by 3,600 seconds, divide by 8 to turn bits into bytes, and divide by 1,024 to turn megabytes into gigabytes — about 0.44 GB per hour for each Mbps. A 5 Mbps stream uses about 2.20 GB per hour, a 25 Mbps 4K stream uses about 10.99 GB per hour, and a 1 Mbps music stream uses about 0.44 GB per hour. Over a month, one hour of 4K streaming a day adds up to roughly 330 GB.
What speed do I need for 4K streaming?
A single 4K stream needs about 25 Mbps of steady speed, so a 50 Mbps connection is comfortable for one 4K stream with room for other uses. For two 4K streams at once, aim for 100 Mbps. The download-time mode on this page can also show how long a 4K movie file takes to download at your speed.