Fan trained plum trees grow to an eventual height of around 2 m (7 ft). Although the shortest of all the forms, they will grow to a width of around 3 m and are really only a practical proposition when grown against a wall (not north-facing). If you have that sort of wall space available, this is the form for you.

Bush trained plum trees are free-standing and are taller than the pyramid form - around 4m when mature. They do have one advantage over the pyramid form however, the branches and foliage is held around 1 m (3 ft) high from the ground - this makes mowing around the tree  much easier. The downside is that some of the fruit will be too high to pick without the use of a ladder. 

Half Standard trained plum trees are again free- standing and will grow to a height of around 6 m (20 ft). This is a largish tree and only suitable for medium to large gardens. It will produce a mass of plums each year, most of them needing a ladder to harvest.

Standard plum trees reach a height of around 8 m (28 ft) at maturity - on your own head be it if you plant one of these in anything but a large garden. They will produce enough fruit to feed your entire neighbourhood and you will definitely need a decent sized ladder to pick most of the fruit.