I always hear to play moves that are "bigger". How do you figure out how "big" a move is, especially in the early game where it is not obvious to a beginner how many points can come from a move?

Generally you're not trying to do an exact point assessment for moves in the opening. There are a few heuristics you can follow: corners, then extensions along the side, then the center is a generally good order. The border between your area of influence and your opponents's is usually big. When the board is still fairly open, playing in the widest unclaimed area is usually a good idea. Making a group safe (or making your opponent's group vulnerable) can often pay off later. Adding stones to an already safe group is usually not too big, unless it allows you to attack your opponent or keeps you from being sealed in.

All of this type of advice is subject to the actual board position in question, of course. As you play more, you'll develop a sense of what kind of moves to look for.

Hi Valoz,

Good question ( and tricky to answer ).
Supplement to jeromie's post: as he mentions,
the global context is key. For example, the same local move could be small
on one board, but the biggest on another board.

Experience, study, reviews, help from good teachers, etc. are nice components.

At your beginner level, you cannot figure out the size of moves well. Instead, apply this rule of thumb: first, defend the life of your important groups. Second, play other big moves, where big is related to the size of regions they are played in.

Join the club. How many points an opening play gains is not necessarily obvious to anybody. For instance, we now think that the opening play on the 4-4 gains about 14 points. But traditionally, pros thought that it gained only about 10 points. As the game develops and positions become more definite, how much plays gain becomes clearer, but indeed, at the beginning of the game how much plays gain is not very clear.

The best way to get a feel for the size of plays is to look at and go over pro games, particularly games by Takagawa and Fujisawa Hideyuki (AKA Shuko), who were known for their skill at the opening. After that, the best advice, IMO, is that of Takemiya: Make the plays that you want to play. Before you develop a feel, that can be disastrous advice, unless you are playing against strong players, who can show you when and where your plays are too small. Beginners often continue play in a local area long after the plays have become relatively small. You get an idea in your head and it is hard to let go of it. I know, because I did that when I was a beginner.

Currently, the best player in the world is AlphaGo, and I am including one of its games against itself, with brief comments about its big plays in the opening.

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Everything with love. Stay safe.

In the alphago vs. alphago game cited by Bill, the last move is another example of a big move (if such move occurred in my games I would rather call it a "lucky punch" ). As a quick exercise: how big is the last move in points?

As a 20 kyu I wouldn't worry about trying to put a numerical value on your opening moves. Instead read "Opening Theory Made Easy" by Otake, and the first chapter of Yilun Yang's "Fundamental Principles of Go" in which he categorises various opening moves into 4 classes of size. That will allow you to make comparisons like "play in empty corner" is bigger than "play in middle of side where both players have good potential" is bigger than "play in middle of side where only 1 player has good potential".