weigh the snake.
Feed items 10% to 13% of the snake's weight.
Examples - if the snake weighs 15 grams, you'd feed a 1.6 gram pinky. If the snake weighs 30 grams, you could feed 2 pinkies totaling 3.6 grams, or a single small fuzzy of the same weight. If your snake weighs 100 grams, you'd feed a small mouse (a Hopper or small adult) weighing about 12 grams...... and so forth.
Just as a point of reference, I have records dating back to when I obtained my snake a little over 2 years ago. When I obtained Rufus, he was roughly 3 to 4 months old, was about the same size as your snake, he weighed 52 grams, and was eating large fuzzies around 6 grams each. I put him on 8 gram hoppers when he hit 75 grams. He was on small adult mice (12 to 15 grams) within a year. He's a little over 2 years old now, weighs almost 400 grams, and is just shy of 4 feet long. He's currently eating a 30 gram mouse every 10 days. (The 10% to 13% rule applies to growing babies and young snakes. Once they are adults, you can get by with a 30 gram mouse every 10 to 14 days).
If you don't have a scale and can't weigh the snake, a lot of folks go by feeding an item around 1-1/2 times the diameter of the snake's body at its thickest point. Just looking at the pics of your snake that you provided, I'm going to guess your snake could easily be eating small fuzzies right now. But pictures can be deceiving, I'd still go by weight.
