From left to right on the image we have Size 1 / 2 / 3 of a Smoke Colour pacifier. This is an easy way to tell the difference between the sizes you receive.
One of the most common questions we get about sizing is the end of the teat looks a lot smaller than the current pacifier the child uses. This is due to the teat swelling with heavy consistent use. Please refer to the care instructions for more info