How much volume do I need?
1 liter of volume supports 2 lbs of weight.
An 180 lb rider will need at least 85 liters of volume just to stay afloat. 85 liters may be great for a pro in the surf, but for a beginner paddling in a lake, that would be an awful experience.
Buoyancy is what creates the stability in the board. A beginner around 180 lbs. will want to double the figure, so in this case a board around 200 liters of volume would be great.
Note: You can always ride a board with too much volume. It’s when you ride a board with too little volume that the degree of difficulty increases. Be reasonable about your ability when choosing board size.