Add the activities that overlap, allow spare capacity, and check upload separately. A 4K stream, a video meeting and a large download have different requirements. Device counts alone cannot tell you which package to buy.
Once you know the speed you need, use our London broadband overview to compare local coverage and networks.
Build a picture of the busiest hour
List what is genuinely happening at the same time. Include streaming screens, work calls, cloud gaming, backups and large downloads. Do not count the same person twice unless they really use two demanding services at once.
Then decide which activities can wait. Scheduling an overnight backup or pausing a game download during a meeting can change your requirements without changing your subscription.
Use service requirements as inputs
Netflix recommends a stable 15 Mbps connection for one 4K stream. Zoom lists approximately 3 Mbps download and 3.8 Mbps upload for a 1080p video call, with actual needs affected by the meeting mode and video quality. These are service-specific figures, not universal requirements for every platform.
Our estimator uses openly stated allowances and an additional capacity margin. Treat the result as a planning range: applications change their usage, and the broadband connection is only one part of the path.
Work through a household example
Imagine two Netflix 4K streams plus two 1080p Zoom calls. Using the published figures gives 2 × 15 + 2 × 3 = 36 Mbps of downstream demand. Adding an illustrative 25% planning margin gives 45 Mbps. The two calls separately imply 7.6 Mbps upstream before allowing for other uploads.
That arithmetic does not mean a 45 Mbps service is guaranteed to work perfectly. It omits browser bursts, software downloads and fluctuations. It does show why an ordinary streaming household should examine its workload before assuming it needs a gigabit.
Large downloads change waiting time
A video stream mainly needs enough sustained capacity to keep playing. A large download can use spare capacity to finish sooner. A decimal 50 GB file contains 400,000 megabits, so dividing 400,000 by the achieved Mbps gives an ideal transfer time in seconds.
At 100 Mbps that calculation is 66 minutes 40 seconds; at 500 Mbps it is 13 minutes 20 seconds; at 1,000 Mbps it is 6 minutes 40 seconds. Real downloads take longer when servers, Wi-Fi, overheads, storage or other traffic constrain the transfer.
Buy for the problem you want to solve
If your current service handles simultaneous activity but downloads feel slow, a higher tier primarily buys back waiting time. If calls break up when files are uploaded, investigate upstream capacity and competing traffic. If just one room is poor, test the indoor connection.
Choose the next available package above a sensible planning range, then compare its total cost with the lower tier. The site does not receive a live quote for your address and cannot guarantee a particular household experience.
Your questions, answered.
How many devices can 100 Mbps support?
There is no reliable single number. Many idle devices may use very little bandwidth, while a few active video streams or downloads can use much more.
Is the estimator a speed test?
No. It calculates a planning estimate from selected activities. It does not measure your connection or verify availability at your address.
Sources & further reading
Official information behind this guide. Links checked 29 October 2026; individual datasets retain their stated reference dates.