When to switch feed? Help.

[AmyReed]

Right now he's on adult mice, but I feel this is not enough for him and am under feeding. I fear that small rat would be too big for him. I don't have a scale, need to get one.
What in your guys opinion should I be feeding this guy for his size?

Here he is with two dollar bills for size reference. He was born in July 2015.

http://i1345.photobucket.com/albums/p662/amy_reed2/image_zpsoalw2052.jpeg

http://i1345.photobucket.com/albums/p662/amy_reed2/image_zpseqtsq5py.jpeg

[bcr229]

Go with weanling rats rather than smalls.

I switch mine over to rat pups after they've taken a few mouse hoppers.