What internet speed you actually need for 4K streaming

The numbers that matter

For a single stream, roughly 8 Mbps is enough for reliable HD, 15 Mbps makes it comfortable, and 25 Mbps or more is what you want for 4K. Those figures are per simultaneous stream, so two 4K televisions running at once means planning for around 50 Mbps of genuinely available bandwidth.

Note the word available. If somebody is uploading a large backup or a games console is downloading a patch, that capacity is not there for you, no matter what your package says.

Those numbers are deliberately a little above the theoretical minimum. The minimum is the speed at which a stream plays if nothing else ever goes wrong, and something always goes wrong, whether a brief wireless dropout, a neighbour's router or another device waking up. Budgeting a margin is what turns "it works" into "it works every evening".

Where the bitrate figures come from

It is worth understanding the arithmetic, because it makes the recommendations predictable rather than arbitrary.

A video stream has a bitrate: the amount of data per second needed to reproduce it. Typical live broadcast encodes land roughly as follows.

• SD is generally in the region of 1 to 3 Mbps.
• HD at 1080p, encoded with H.264 as most live channels still are, typically sits between 5 and 8 Mbps.
• 4K, which almost always uses the more efficient HEVC codec, typically runs between 15 and 25 Mbps depending on how much motion is in the picture.

Those ranges are typical rather than fixed. A football match, with its fast motion and its crowd of moving detail, needs a higher bitrate to look clean than a studio news programme, and encoders allocate accordingly. It is why sport is where marginal connections reveal themselves.

Your connection needs to exceed the stream's bitrate with headroom, not match it. A 20 Mbps stream on a 20 Mbps line will stutter, because the line never delivers exactly its rated speed for every second of an hour.

8K, and what the name actually means

We should be straight about this, given what we are called. Genuine 8K live broadcast content is rare today; the name signals the headroom the service is built with rather than a promise that every channel is 8K. Where 8K does exist, typical encodes are in the region of 50 to 100 Mbps per stream, which is why it will remain a specialist proposition for some time.

The practical value of that headroom is in the tier below it. A platform engineered to carry very high bitrates comfortably is a platform that does not strain when the 4K channels are busy, which is the part you actually benefit from this year.

Budgeting for a household, not a screen

The mistake people make is treating bandwidth as a household figure. It is not; the requirement is per simultaneous stream, and it adds up.

A useful way to plan is to add up the worst realistic evening in your house. One 4K television and one HD stream in a bedroom is roughly 25 plus 15, so 40 Mbps of viewing. Add whatever else runs at the same time: a games console downloading in the background can occupy a great deal of a connection, and smart home devices, phones and laptops each take a small share.

Then leave a margin of perhaps a third on top. A line that is running at ninety per cent of capacity every evening is a line that will buffer the moment anything unexpected happens.

Remember too that each simultaneous stream on an IPTV subscription needs its own device slot, chosen when you order on the pricing page. Bandwidth and slots are separate limits, and running out of either produces stopping and stuttering; see adding a second device if you are not sure which one you are hitting.

Upload speed is almost irrelevant

Watching television is a download activity. The upstream traffic is a trickle of acknowledgements and requests, measured in tens of kilobits, and no streaming service has ever been limited by a viewer's upload capacity.

The one way upload matters is indirectly. On most home connections, saturating the upstream link degrades the downstream one, because the acknowledgements your device needs to send get stuck in a queue behind your outgoing data. A cloud backup running at full tilt, a large file being shared, or a video call can therefore cause buffering that looks exactly like a download problem. If your stream falls apart at the same time every night, check whether a backup is scheduled then.

Why stability beats speed

A stream is a continuous conversation. Each brief interruption forces the player to refill its buffer, and if interruptions arrive faster than the buffer refills, playback stops.

This is why a consistent 20 Mbps connection can outperform a 200 Mbps one that experiences packet loss. Speed tests do not measure this at all, which is why they so often show a healthy result on a connection that streams badly.

Packet loss is the specific villain. A lost packet must be detected and re-sent, which takes time the player does not have. Loss of even a fraction of a per cent, sustained, is enough to make a stream unwatchable while leaving a speed test looking perfectly respectable.

Latency and jitter versus bandwidth

Three different measurements get confused constantly, and separating them is the most useful thing on this page.

• Bandwidth is how much data per second the line can carry. It is the number your package advertises.
• Latency is how long a single packet takes to arrive. For streaming, ordinary latency barely matters; a fraction of a second of delay before a channel starts is invisible.
• Jitter is how much latency varies from packet to packet, and this is the one that ruins streams. A connection delivering data at a steady rhythm keeps the buffer full. One delivering in irregular bursts empties it, even when the average over a minute looks fine.

Speed tests report bandwidth and sometimes latency. Almost none report jitter or packet loss, which is precisely why a good test result so often accompanies a bad picture.

Testing the right thing

Instead of another speed test, run a continuous ping to a well-known address for a few minutes while streaming. Steady low numbers mean a healthy line. Numbers that spike into the hundreds, or replies that go missing entirely, tell you exactly where your buffering comes from.

Do this test over Ethernet and again over Wi-Fi. If Ethernet is clean and Wi-Fi spikes, you have found your problem and it is not your provider.

Two refinements make the test far more informative. Run it at the hour when the problem occurs rather than at a convenient time; an afternoon test on an evening problem tells you nothing. And run it while streaming rather than on an idle connection, because a line that looks flawless at rest and falls apart under load is an extremely common pattern, and one that only a test under load will reveal.

Wi-Fi realities

The speed your router advertises and the speed your television receives are different things, and often dramatically so.

Wireless capacity is shared among everything connected, drops with distance, and drops further with every wall. A device showing three of five bars is frequently receiving a fraction of what the router can deliver. Worse, wireless throughput is variable in a way wired connections are not: it fluctuates second by second as interference comes and goes, which is jitter by another name.

The practical implication is that a household with a fast connection can still fail to deliver 25 Mbps steadily to a television in a back bedroom. Before concluding that your internet package is inadequate, test at the device rather than beside the router. If those two numbers differ substantially, the problem is your wireless, and upgrading your broadband will change nothing at all.

Where you can, wire the main television. Where you cannot, use 5 GHz rather than 2.4 GHz, and consider powerline adapters, which are usually a bigger improvement than a new router. There is more on that in why streams buffer and how to fix it.

Recommended plans by household

These are guidelines rather than rules, and they assume a connection that delivers its rated speed reasonably consistently.

• One person, one HD television. Around 25 Mbps is comfortable. Below about 15, you will want the SD variants of busy channels during peak hours.
• A couple with one 4K set and occasional phone viewing. Around 50 Mbps gives you room to breathe.
• A family with two televisions, one of them 4K, plus phones and a games console. Plan for 100 Mbps or more, chiefly because of what everything else in the house is doing rather than what the televisions need.
• A busy household with three or more simultaneous streams, or anyone regularly watching sport in 4K. Above 150 Mbps, and wire the main screens.

If your line is well below these figures but stable, you will still have a perfectly good experience on HD. Stability is the variable that decides whether you are happy; the headline number only decides how many screens you can run at once.

When upgrading is worth it

Upgrading your package helps when several people genuinely stream at once, or when your current line cannot sustain a single HD stream cleanly. It does not help at all when the bottleneck is wireless interference, an overheating streaming stick, or peak-hour throttling.

Diagnose before you spend. It is common to pay for a faster package and see no improvement whatsoever, because the extra capacity was never the limiting factor.

If you are choosing between spending on a faster package and spending on an Ethernet adapter for the main television, buy the adapter first. It costs a fraction as much and, in our support experience, fixes far more streaming complaints than a faster line does.

Next steps

Run the ping test described above, at the hour your problem occurs, on the device that has it. That one measurement will tell you more than a fortnight of speed tests, and it is the number our support team finds most useful when someone reports buffering.

If the result looks healthy and the picture still stops, work through why streams buffer and how to fix it, which sets out the remaining causes in the order worth checking. If you are still stuck after that, send us your order number, your device, whether it is wired or wireless, and whether the problem affects one channel or all of them. That combination of details is usually enough for a diagnosis rather than a questionnaire.