Skateboard Decks Explained
Skateboard Deck Width
Skateboard decks come in all different shapes and sizes. Decks are primarily sized by the width in inches starting from 7.125" and going all the way up to 10.0". Most people tend to stay in between 7.5" to 8.5", with kid's decks and minis typically coming in narrower than 7.5"...and cruisers and vert boards coming in above 8.5". The best way to determine what size you should get is to consider for your height and weight and the kind of skateboarding you are most interested in.
Skateboarders who are more interested in the more technical side of skating, such as flip tricks, ledges, or manual pads, might prefer a smaller deck. Smaller decks are much easier to flip and spin, but can be harder to land on.
Bigger boards are ideal for bigger skaters and people mainly interested in transition skating, including quarter pipe, bowl, and pool skating. Bigger decks are also better for people doing big stair sets, gaps, etc.
Skateboard Deck Shape
Deck shapes can be vary in the sense of being more square and blunt, or more pointy and narrow. Some decks are flatter, and some decks have more concave.
Concave is just that; the inward curve of the surface of a skateboard. The more concave you have, the easier it is to flick your flip tricks. Decks with more concave also retain their shape better. Decks with less concave offer a more consistent flow and a flatter area for your feet, which can help with landings. When it comes down to it, concave is strictly a matter of personal preference.
Skateboard Deck Length
Most skateboard decks (aside from longboards, of course) are in the 31"-33" range. The length of a skateboard doesn't really matter that much, and is typically a function of the overall dimensions and shape of the board.