On my mini chihuahua, half-year-old, the size of S just right, also on growth will be. Very well sits and looks. I recommend
Nice though the top i don't like very much where the strap is tied. Perfect size as it is quite adjustable
Funny harness, sewn qualitatively, bought a gray size m, for a dog 4,5 kg came well, but tighten to the end. Not yet walked, did not wash, if it turns out to be g, i will finish) and in the meantime i recommend.