Start from per-stream requirements, then multiply
A single 4K stream needs roughly 25 Mbps sustained; FHD needs 10-15 Mbps; HD needs less still. The mistake most households make is testing their internet speed once, seeing a healthy number, and assuming that number applies per device rather than being shared across everything running at once.
Worked example: a household running three screens
Two 4K streams plus one FHD stream simultaneously needs roughly 25 + 25 + 15 = 65 Mbps of actual sustained throughput, not counting other household internet use (video calls, downloads, smart home devices). A 100 Mbps plan handles this comfortably; a 50 Mbps plan will struggle the moment all three run together.
Why a fast speed-test result can still mislead you
A speed test measures peak burst speed for a few seconds, not sustained throughput over a two-hour movie or a live sports broadcast. Run a speed test on the actual device that's streaming, during the actual time of day you usually watch, for a more honest picture than a single daytime test on your phone.
Reducing total bandwidth need without upgrading your plan
- Drop secondary/background screens to HD or FHD instead of 4K
- Stagger simultaneous 4K viewing where possible rather than running three at once
- Prioritize your main screen's traffic with router QoS settings — see our router optimization guide
How connection count and bandwidth interact
Your plan's simultaneous connection limit and your actual internet bandwidth are two separate constraints — see our multi-device family guide for sizing connection count correctly alongside this bandwidth math.
If multiple screens are buffering at once, check the math above before assuming it's a service issue — and if you're still stuck, work through our full buffering fixes guide or message us with your setup.