I have seen it recommended that when you are feeding multiples, since you can't really use the girth of the snake to gauge the size of the meal, go by weight instead. For a growing snake, feed about 10-15% of its body weight.

I started doing this with mine and it seems to be working out well.

Right now, feeding one of your mice falls in that range for your snake.

However, as Adriana (Argentra) said, you also need to go by the signals your snake is giving you. Does he continue to act hungry after being fed? Or does he go to his hide to digest pretty quickly? Does he start acting hungry again only a few days after eating, or does it take close to the full 5 days?