is the female bigger than the male

They say the females are always larger in the belly area than the males of the same age. I told the sex of my GF by his rectum though.

how do u do that

It is hard to sex young goldfish, but you can tell the sex of the mature ones by the shaper of their vent. Females have a wider vent (anus) than males. In addition, when you look at the fish from the side you will see that males have a concave (sunken) vent and females have a convex (raised) vent.

yes, females are larger in size compared to the males, right now in my 5 gallon tank i have an black moor and an comet(sparkel), and the blackmoor(jojo) is really heavy sometimes i think shes constipated, but my comet is in excellent shape. if u look on top for the, females are uneven and lean to the left if they stop flapping thier fins for a second or two . and my comet is health and shiny and hes more slennder and slim. i hope it answered ur question

Here's a pic displaying both male and female
fish.

Another way to tell male fish (when they're old
enough) is they get white dots (breeding stars/
tubercules) on their gill plateand along the front
edge of the pectoral fins. Here's a pic to show that.

And another one.

crystal clear show...thank you