Weight, not volume

What it says

The net quantity statement shall be in terms of fluid measure if the commodity is liquid, or in terms of weight or mass if it is solid, semi-solid or viscous, or a mixture of solid and liquid. A wax melt in a customer’s hand is solid, so it is a weight.

There is a trade custom escape, and it does not help here

The section allows a different unit where there is a firmly established general consumer usage and trade custom, and where it still facilitates value comparisons. Melts are sold by ounces across the trade, so the custom points the same way the default does.

The conversion is yours to make

The catalog gives capacity in milliliters because that is a property of the container. Turning that into a fill weight requires your wax, your fragrance load and your fill height, which is why no catalog can do it for you.

Wax is lighter than water

Around nine tenths, varying by wax type and by how much fragrance oil is in it. So the weight is always less than the capacity figure in grams, and treating the two as interchangeable overstates what is in the jar.

Overstating is the direction that bites

A declaration has to accurately reveal the quantity in the container, and 500.25 permits variations only from ordinary distribution and from unavoidable deviations in good packaging practice, not from a figure that was never measured.

So weigh it, every time the formula changes

A new wax, a higher fragrance load or a different fill height all move the number. Reweighing takes one jar and a scale, and it is the only evidence that supports what the label says.

Fluid ounces and ounces are not the same unit

A jar described as 8 oz in a catalog is 8 fluid ounces, a volume. The ounce on your label is a weight. They share a word and nothing else, and confusing them is the single most common labeling error in this category.

References