Bandwidth Calculator

This calculator answers three everyday networking questions: how long a download or upload will take at a given speed, how big a file will be from its bitrate and duration, and how fast a connection you need to move a certain amount of data by a deadline. Presets cover common music, streaming, upload and video-call bitrates, and a chart compares results across typical speeds or bitrates.

It handles both decimal units (MB, GB) used by internet providers and drive makers, and binary units (MiB, GiB) used by many operating systems.

Time = file size (bytes) × 8 ÷ effective speed (bits per second)

File size (bytes) = bitrate (bits per second) × duration (seconds) ÷ 8

Internet speeds are quoted in bits per second, while file sizes are in bytes, and a byte is 8 bits. That factor of eight is the most common reason downloads take longer than expected: a 100 Mbps connection moves at most 12.5 megabytes per second. Real transfers also lose some capacity to protocol overhead, so the calculator lets you subtract a percentage.

A 4 GB game update at 100 Mbps with 6% overhead takes 5:40.

An hour of 4K streaming at 15 Mbps uses 6.75 GB of data, against 2.25 GB for HD at 5 Mbps.

A 50 GB backup overnight in 8 hours needs at least 14.8 Mbps of upload speed.

A gigabyte (GB) is 1,000,000,000 bytes, but Windows and some other software count in gibibytes (GiB) of 1,073,741,824 bytes while still labeling them GB. That is why a 1 TB drive shows up as about 931 GB on a Windows computer. Network speeds always use decimal units, so 1 Mbps is exactly 1,000,000 bits per second.

Add up what people do at the same time. Two 4K streams at about 15 Mbps each, two HD video calls at around 3 Mbps each and some browsing and background updates come to roughly 40 to 50 Mbps of sustained use, so a plan with comfortable headroom above that avoids slowdowns at busy times. Upload speed matters for video calls, cloud backup, livestreaming and sending large files, and on many cable and DSL plans it is a small fraction of the download speed. If you work with large files, use the deadline mode to check whether your upload speed can keep up.

On capped or mobile plans, the file size mode helps you budget. Streaming video is usually the largest use: an hour of HD video can use more than 2 GB, so a few hours a day adds up quickly. Many apps let you choose a lower streaming quality on mobile data, and music streaming uses only around a tenth of a gigabyte per hour.

Advertised speeds are maximums. WiFi interference and distance from the router, other devices sharing the connection, busy servers at the other end and network congestion at peak times all reduce throughput. Upload speeds on many home connections are far lower than download speeds. For a realistic estimate, run a speed test from the device you will use, close to the time you plan to transfer, and enter that measured figure here.