So what is the right board size for your particular chess pieces, really? One rule of thumb goes like this: The king’s diameter should be about 75 % of the field size.
Numbers are hard. Over here we use a simpler rule of our own. More practical too. Here’s how we do it:
Take a king and a queen and place them on diagonally adjacent squares. Place a bishop between the royal pair. See if the bishop has any chaperoning elbow room. If not, you got some shopping to do. Your board is crowded. Bigger is better.
Here’s a detailed video: