It has long been understood by the informed that the size of memory quoted when you buy your new shiny telephone will not be what you actually get. Rather it will be, but a proportion of that space will already be used by the operating system and whatever bloat the manufacturer and carrier choose to add. Most of this filled space will not be possible to reclaim.
Which, the British Customer reviews and advocacy organisation, looked into it and has produced the above infographic which perfectly illustrates the situation. The most interesting point is that the graphic makes it very clear where the majority of the problems are coming from – the manufacturers. The top three phones are made by Apple and Google who feel no need to differentiate with their own skins and extra apps and hence can provide the most free space. It also makes the point – if you need a lot of space on your phone get the biggest size you can afford – there’s no way to upgrade later.