I know I am not strong on estimating sizes in millimeters. I do better in relative terms. This green metallic bee is 1/2 the size of other green metallic bees I have photographed in the same area. I did see some of the larger green metallic bees on this trip but these tiny ones were more numerous. It is roughly 1/4 the size of a honey bee. The mimosa flower it is on forms a sphere about the size of a small gumball.
This is an example of the larger green metallic bees: