Your broadband provider promises "ultrafast speeds up to 900Mbps" and you nod along assuming your files will download quickly. Then a 4GB game update takes an hour. The gap between advertised speed and experience comes down to a few specific, entirely explainable factors.
Bits vs Bytes: The First Confusion
Internet speeds are measured in bits per second. File sizes are measured in bytes. 8 bits = 1 byte. A 100 Megabit per second (100 Mbps) connection transfers 12.5 Megabytes per second (MB/s). To convert: Mbps ÷ 8 = MB/s. Our data storage converter handles all these unit conversions. Our time calculator helps convert download time estimates to hours and minutes.
Download Time Formula
File size (bits) ÷ download speed (bits/second) = download time (seconds). Example: 5 GB file on 100 Mbps: 5 GB = 40,000 Mb ÷ 100 Mbps = 400 seconds ≈ 6.7 minutes (theoretical maximum under perfect conditions).
Why "Up to" Speeds Are Misleading
Your actual speed depends on: network congestion during peak hours | distance from the street cabinet (FTTC speeds degrade with distance) | Wi-Fi interference (often the real bottleneck, not the broadband line) | server capacity at the download source | quality of your router. ASA rules require ISPs to advertise speeds that at least 50% of customers achieve during peak hours — but the "up to" figure remains optimistic.
What Speed Do You Actually Need?
- HD streaming (Netflix): 5-10 Mbps per stream
- 4K streaming: 25 Mbps per stream
- HD video calls: 3-5 Mbps per person
- General browsing: 10-20 Mbps is comfortable
- Household of 4, multiple simultaneous streams: 80-150 Mbps is comfortable
Upload Speed: Often Forgotten
Most broadband is asymmetric — download is much higher than upload. For video calls, uploading large files, or working from home intensively, upload speed matters significantly. Check your plan's upload speed explicitly — it's not always advertised prominently.
Test Your Actual Speed
Run a speed test (Speedtest.net, Fast.com, or your ISP's tool) from a device connected by Ethernet cable — not Wi-Fi — for an accurate reading. If results consistently fall far below the quoted package speed, you may have grounds to complain or switch under Ofcom's Automatic Compensation Scheme.
Further reading: Ofcom covers consumer broadband rights, speed claims, and how to complain. Read Ofcom's guide to broadband speeds and your rights.