Length
More length can improve glide, paddling and early wave entry. It also increases the rail line and changes how much board must be redirected through a turn.
Width
Width can create stability and planing area, but where the width sits is important. Width through the nose may support paddling, while width through the tail can influence speed, lift and turning feel.
Thickness
Thickness contributes volume, yet a thick centre with refined rails behaves differently from thick rails throughout the board. Distribution affects both flotation and how the rail engages the water.
Read dimensions together
Use the numbers to compare, then look at outline, rocker and intended use. A dimension sheet is a starting description, not a complete prediction of performance.