The standard size for a freestanding dishwasher is 85h x 60w x 60d. You can find smaller ones that are made to fit in a more confined space but the majority of dishwashers you see will be the above dimensions. The main difference between them all will be the amount of additional programs and the place settings available.
Place settings refers to the capacity of the dishwasher, with 1 place setting being 1 persons cutlery amount for one meal. This is made up of a knife, fork, soup and tea spoon, dinner, soup plate and dessert plates, a glass, tea cup and saucer.
On top of the various size place settings you can also find different machines having different wash programmes and temperatures, energy ratings, water consumption and availability of delay start and half load programmes. These variations allow you to find a machine that will be perfect for what you require.