There are multiple metric units to choose from! This tutorial goes through the process of choosing the best metric unit to use for measuring the mass of a given object.
The most common aphids on houseplants are the light green ones (pear aphids), but aphids can also be found colored pink, white, grey and black. Additionally, winged aphids can appear when colonies are established and fly to infect new plants. Juvenile aphids (nymphs) look like smaller versions of the adults.
Aphids are very small (only a few millimeters long), soft-bodied insects. They have two little tubes at the end of the abdomen called cornicles. They have small eyes, and sucking mouthparts. They are often green, but may be red, black or brown. They move slowly, and don't jump or hop.