Lilly on the right (chuihuahua) is 2 1/4lbs wearing her size 1 in pink.

For sizing, you may find the following a helpful guide for a quick assessment ( inches refer roughly to length measurements). If in doubt, don't try the item
on your pet if you would like to make a return):

SIZE CHART: DOG T-SHIRTS
SIZE	BACK	CHEST	NECK
00	5 1/4	8 - 9 1/4	5 1/2 - 6 1/2
0	7 1/4	9 1/4 - 10 3/4	5 1/2 - 6 3/4
1	8	10 1/2 -12	6 1/2 - 7 1/2
2	9 1/4	12 - 14	7 1/2 - 8 3/4
3	10 3/4	14 - 16	8 3/4 - 10 1/2
4	12 1/2	16 - 18 1/2	10 1/2 - 12
5 (Was Size 4.5)	14	18 1/2 - 20 1/2	12 - 13 1/2
6 ( Was Size 5)	16	20 1/2 - 23 1/4	13 1/4 - 15 1/4