Why Your Broadband Is Slower Than You Paid For

You pay for 100 Mbps. Your download manager says 11 MB per second. Nothing is broken and nobody is lying to you.

The units are different

Connections are sold in megabits per second. Files, download managers and operating systems all work in megabytes. There are eight bits in a byte.

100 Mbps / 8 = 12.5 MB per second

That is the whole of the main discrepancy. A 100 Mbps connection downloads a 1 GB file in about 82 seconds at best, not the 10 seconds the number superficially implies.

The tell is the capital letter. Mbps is megabits. MBps is megabytes. One character, a factor of eight.

Nobody is being deceived exactly, but the choice of unit is not accidental either: megabits produce a bigger number for the same speed, and marketing departments know this.

Why even 12.5 is optimistic

Several things sit between the advertised figure and what arrives.

Protocol overhead. TCP/IP headers, acknowledgements and retransmissions typically consume 5 to 10%.

The server. You cannot download faster than the other end will send, and popular files are frequently rate limited.

Wifi. The advertised speed is to your router, not across your house. Walls, distance and interference all reduce it, often dramatically. A gigabit connection over poor wifi can deliver less than a tenth of it, and the connection is not the problem.

Contention. Home connections are shared. Evenings are slower than mornings, consistently.

Everything else on your network. Streaming, cloud backup and system updates all take a share, usually without telling you.

A realistic figure is around 80% of the theoretical, and lower over wifi at distance.

What speed you actually need

Less than you have probably been sold. Streaming is the usual justification and it needs surprisingly little:

Use	Roughly
Standard definition video	3 Mbps
1080p video	5 to 8 Mbps
4K video	25 Mbps
Video call	2 to 4 Mbps
Online gaming	Under 5 Mbps

A household streaming three 4K films simultaneously needs about 75 Mbps.

Beyond roughly 200 Mbps, most people are paying for a number rather than an experience. The money is usually better spent on a decent router, or on running a cable to wherever it actually matters.

Latency is not speed, and it is often the real problem

Bandwidth is how much data flows per second. Latency is how long a single packet takes to get there and back.

For downloading large files, bandwidth dominates. For video calls, gaming and how responsive browsing feels, latency matters far more.

A 1 Gbps satellite connection with 600 ms of latency is worse for a call than a 20 Mbps fibre line with 10 ms. The satellite wins every download comparison and loses every conversation.

This is why “upgrade your speed” is so often the wrong answer to a connection that feels slow. Test the latency before paying for more bandwidth, because more bandwidth will not fix it.

Wifi is usually the bottleneck

If your speed test is fine on a cable and poor on wifi, the connection you are paying for is working and the problem is inside your house.

Things that help, roughly in order:

• Move the router. Central, elevated, not in a cupboard or behind a television.
• Use 5 GHz for anything nearby. It is faster and less congested, with shorter range.
• Run a cable to the things that matter most. A desktop, a games console, a television.
• Mesh or a second access point for a large or awkwardly shaped house. Usually better value than a faster package.
• Check the router itself. An old one supplied years ago may not support the speed you now pay for.

Working out how long something will take

The download time calculator handles the bit-to-byte conversion and applies a realistic discount, which is usually much closer to what you will see than the theoretical figure.

For reference, at a realistic 10 MB per second:

• A 4 MB photo: instant
• A 100 MB album: 10 seconds
• A 4.5 GB system update: about 8 minutes
• A 100 GB game: nearly 3 hours

That last one is why game downloads feel like they take forever even on a fast connection. The files genuinely are enormous, and no plausible consumer speed makes 100 GB quick.