Bandwidth Calculator
Convert a data-transfer size and duration into a throughput rate in megabits per second. Useful for sizing internet plans, backup windows, and streaming budgets.
Last updated: September 2026
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About this calculator
Bandwidth is data per unit time. In networking it is measured in megabits per second (Mbps) — note lowercase b for bits, not bytes. A megabyte (MB) is 8 megabits, so a 100 MB file is 800 megabits.
This calculator uses the direct definition: throughput = (dataSize × 8) / time. If the file is in MB and the time is in seconds, the answer is in Mbps. For GB and minutes, multiply GB by 1000 to get MB and minutes by 60 to get seconds first, then feed the numbers in.
Real-world throughput is always lower than the link speed because of protocol overhead (TCP/IP headers, acknowledgments, retransmissions) and physical-layer encoding. Sustained transfer over a residential 100 Mbps line usually tops out at 88–95 Mbps in practice; a 1 Gbps link at 900–940 Mbps. That is normal.
How to use
Example — measure a real transfer. You downloaded a 100 MB backup archive in 10 seconds. Enter Data size = 100 MB, Transfer time = 10 s. Result = (100 × 8) / 10 = 80 Mbps. That matches roughly a 100 Mbps plan after overhead. Example — size a nightly backup window. You need to move 50 GB (= 50 000 MB) offsite between 02:00 and 06:00 (14 400 seconds). Required bandwidth = (50 000 × 8) / 14 400 ≈ 27.8 Mbps. A 50 Mbps upstream fits comfortably; a 25 Mbps line does not.
Frequently asked questions
Why megabits and not megabytes?
Networking bandwidth is quoted in bits per second by convention (Mbps, Gbps) so that raw link capacity is decoupled from file-system byte sizes and from the 1000-vs-1024 ambiguity. File sizes use bytes (MB, GB). The factor of 8 is the bridge: 1 byte = 8 bits, so a 100 MB file at 100 Mbps takes 100 × 8 / 100 = 8 seconds in the ideal case.
MB or MiB?
This calculator treats 1 MB = 1 000 000 bytes (the SI definition), matching how ISPs and disk manufacturers quote sizes. If your source uses MiB (mebibytes, 1 MiB = 1 048 576 bytes), multiply by 1.048576 before entering. For most casual uses the ~5% difference is inside the noise of overhead anyway.
What throughput do I need for streaming?
Rough numbers from streaming platforms: 1080p at ~5 Mbps, 4K at ~15–25 Mbps, live 4K HDR at ~40 Mbps. Multiply by the number of concurrent streams in the household and add ~20% headroom for game updates and video calls. This calculator lets you check a given file/time example against those thresholds.
Why is my actual speed lower than my plan?
Two reasons: (1) protocol and physical-layer overhead eats 5–15% of the raw link rate; (2) the bottleneck may be anywhere between you and the server (Wi-Fi, in-home cabling, ISP peering, the remote server). Testing with a big file from a fast host (e.g. speedtest.net) isolates the ISP portion; testing between two devices on your LAN isolates the in-home portion.