How is download time calculated?

Multiply the file size in bytes by 8 to get bits, then divide by your effective speed in bits per second. Effective speed is the line rate reduced by protocol overhead — typically 10–20%.

Why is my real download slower than my advertised speed?

Advertised rates are line capacities. TCP/IP headers, TLS encryption, Wi-Fi losses, server limits, and shared congestion all take a cut, which is why 100 Mbps rarely exceeds 10–11 MB/s of visible payload.

How long does a 100 GB download take on gigabit?

About 16 minutes under ideal conditions — 100 GB is 8 × 10¹¹ bits, and a gigabit link with 15% overhead delivers roughly 850 Mbps of payload. Realistically, allow 20–30 minutes.

What is the difference between Mbps and MB/s?

Mbps is megabits per second — the ISP’s unit. MB/s is megabytes per second — what your browser reports. Divide Mbps by 8 to get MB/s, then subtract overhead for the true figure.

Should overhead be 15%?

It is a sensible default for TCP plus TLS over a healthy link. Local LAN transfers with large packets can dip under 5%, while congested Wi-Fi can exceed 30%. Adjust to match a measured transfer.

Download Time Calculator | Online Calculators Free

Why your 100 Mbps is not 100 MB/s

Line speeds sell in megabits (Mbps); files live in megabytes (MB) — eight bits to the byte, so 100 Mbps tops out at 12.5 MB/s before losses. On top sit protocol overheads: TCP/IP headers on every packet and TLS encryption on secure downloads. Budgeting 10–20% overhead turns an optimistic number into an honest one.

The transfer formula

Transfer time = file size × 8 ÷ effective speed in bits per second. This calculator uses decimal units — MB = 10⁶ bytes, GB = 10⁹ — matching how ISPs and most storefronts quote sizes. The readable line converts raw seconds into days, hours, minutes, and seconds so multi-hour transfers are obvious at a glance.

Diagnosing slow real-world transfers

If downloads consistently beat these estimates badly, the bottleneck is usually not raw bandwidth: Wi-Fi signal, an older router, server-side limits, DNS issues, or a busy shared link. Wired tests isolate the link before you blame the ISP — or upgrade for the wrong reason.

Worked example

A 5 GB file on a 100 Mbps connection with 15% overhead.
Effective speed = 100 × 0.85 = 85 Mbps ≈ 10.6 MB/s.
40,000,000,000 bits ÷ 85,000,000 bits/s = 470.6 seconds.
Readable result: 7m 51s.

How to use it

Enter the file size and pick MB, GB, or TB.
Type your advertised or speed-tested rate in Mbps.
Keep overhead at 15% unless you have measured your link.
Read the human-friendly duration and the MB/s throughput.