Would a 157 cm snowboard be too short for me if I'm about 6 ft 3

stand next to it and it should come to about ur chin. thats how they usually measure them.

stand right up next to the vertical board, if its between your chin and nose, than its perfect

It really depends what on you ride and the conditions you ride in, plus your weight. I've got boards from 151 to 168 for different days.

A 157 might be on the shorter side for you but if you're riding groomed terrain parks & things like that it could be perfect. l am 5'11, 180lbs and my single ''all-purpose'' board is a directional 157.

We get some huge dumps of snow here (Niseko) and l will grab a longer board for those days.

Do not just pick a board between ur nose & chin that is a rookie mistake
You need to take into account a few things ur height,weight,riding conditions,riding style''all mountain,freeride,freestylefoot size & skill lvl
Once u get those nailed down u can narrow down ur board genre & size, Generally people go largest on freeride boards for stable carving & float in pow, Mid range for an all mountain board & smallest for those park rats.

Some simple guidelines u can follow as well is remembering that the longer the board the more stable it will be for u for high speed carves & float in pow, the shorter the board the easier it will be to maneuver around butter & just dork around on runs.

It depends on ur riding style & what u like to do.

A long board will be more stable, but get too big & it is going to feel unwidely & harder to turn.

A shorter board gives u greater mobility & allows for very agile turning. It also allows u to spin faster. Get a board too short & it will have a tendency to washout on you.

As for size. Weight has more to do with it that ur height. Also consider whether or not u need a wide board. If u have ever gotten a rental & have big feet, u have probably experienced some nasty boot drag.

My guess is ur getting a deal online, but it would be to ur advantage to go to a ski shop & at least have a tech walk u through sizing & help u decide what ride is best for you.

Simply put, the last thing u want to do is drop all the money & the setup does not work. Consider also that u can get years of use out of a board--get the right one.

Probably.

Board sizing is not just about how tall you are and how tall the board is. Every board has a recommended weight range, you should fall within it. If you're super skinny at 6'3 it is possible it could work for you, but l am doubtful.