When it comes to buying a skateboard, there are a lot of different factors to consider, but the most important one is obviously the deck size. The skateboard deck is the actual board itself - it's where you stand on when riding. With that being said, its size can really affect the way you skate and dictate the range of tricks you can do.
Therefore, deciding which skateboard size works best for you, obviously should obviously down to your preferred skating technique. But be careful, as deck size is not referred to by a single measurement. In fact, it's a combination of several measurements: length, width, and wheel base. To make it easier for you, here's a quick explanation.
Width
When you're a beginner, it's advisable to choose your deck according to the width, not the length. Most adult skateboard decks have a width between 7.5'' and 8.75''. If you like to be able to perform vert riding, or in other words, going off ramps and shredding the pool, it's best to focus your search on 8 inch skateboards. If you're a big person and need more room for your feet, a wider deck such as 8 inch skateboards have will give you more surface area to balance yourself. On the other hand, if you're into riding street or making tricks such as kickflips, a board with a smaller width can help you perform better.
Length
The length of the skateboard deck is the distance from the tail and the nose. Usually, it falls between 28'' and 32''. The length of the board grows exponentially to its width. In other words the longer the board the wider it's likely to be. Therefore, the same suggestions referring to width, apply to length as well. It's important to note that there are also longboards which can be much longer than 32''. If you'd like to simply cruise around, a longboard or a much larger board will help you maintain your stability and balance better.
Wheelbase
An often overlooked factor in choosing a skateboard deck is the wheelbase. The wheelbase is basically the distance between the two sets of mounting holes in the back of the deck, where the trucks for the wheels will attach. Like board length and width, it also greatly affects your stability. The wheelbase usually ranges between 13'' and 15''. Taller skateboarders usually prefer a wider wheelbase that is more suited for their centre of gravity.