1 Know your US boot size and back binding angle.
2 Look for the minimum snowboard waist width for your boot size and back binding angle.
3 Adjust accordingly: park 0 | beginner 0 | All mountain +2mm | pipe +3mm | carve/race +5mm
Maximum waist width for beginners The one correspondent to your boot size with the back binding at 0 (zero) degrees. Or just stay within the range in white, from 0 to 15 degrees. Remember, a narrower snowboard is easier to control at first.
Maximum waist width for intermediate/advanced snowboardes Until 1,5cm (15mm) wider than the minimum waist width for your boot size and back binding angle. Think twice before buying a snowboard any wider than that without trying it first. This if you can find one, production snowboards tend to stay within that range.
note: If you want a snowboard in a size (length) but it has a smaller waist width than the minimum suggested in the chart for your boot size and back binding angle, look for a wide version (with a W after the length, like 154W). You may need to round the chosen size because there are not wide versions for every snowboard size.