" A cloudspotter should hold up three fingers with an extended arm. If the individual elements of the layer are wider than all three fingers, the cloud is probably of the lower Stratocumulus genus. If they are smaller than the width of one finger, then it is more likely to be a high layer of cloudlets, called a Cirrocumulus. It is most likely to be an Altocumulus layer when the size of the cloudlets is somewhere between the two – smaller than three fingers and larger than one. "

― , The Cloudspotter's Guide