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Bandwidth Calculator

Available

Calculate how long a download or transfer takes, how much data moves in a given time, or how much bandwidth you need to move data within a deadline — with formulas and optional efficiency.

Calculate

Mode

How long does it take to move this much data?

Accounts for protocol overhead and other traffic. Your assumption — results show both the theoretical and the adjusted value.

Download presets:

Result

The same transfer at common speeds

Throughput only — latency, packet loss, Wi-Fi, server capacity and TCP window limits can keep real downloads below the line rate. Related: Data Storage Converter · Bits & Bytes Explainer

How it works

All three modes use one relation: data volume = bandwidth × time × efficiency. Given any two, the third follows. Volumes are converted to bits and bandwidth to bits per second exactly before calculating; the efficiency percentage (optional) accounts for protocol overhead and is reported separately from the theoretical result.

Frequently asked questions

What is a realistic efficiency?

It depends on the protocol and path. TCP over Ethernet typically delivers roughly 90–95% of the line rate under ideal conditions; VPNs, Wi-Fi and long-distance links can be much lower. Measure your own throughput for planning.

How do I size a link for nightly backups?

Use “Required bandwidth”: enter the backup size and the time window. Add headroom for growth and other traffic on the same link.

Does this account for latency?

No. It calculates throughput only. High latency can limit a single TCP connection below the line rate; parallel streams or tuning may be needed.

Why is my real download slower than the estimate?

The theoretical time assumes the full line speed is available. TCP/IP and TLS overhead, Wi-Fi, other devices, server limits and congestion all reduce it. Use the efficiency option for a rough allowance, or divide your measured throughput by your plan speed.

Mbit/s or MB/s?

ISPs advertise megabits per second (Mbit/s); browsers and download managers usually show megabytes per second (MB/s). Divide Mbit/s by 8 for MB/s — 100 Mbit/s is at most 12.5 MB/s.