This page http://www.ftc.gov/os/statutes/fpla/fplact.html explains the regulations in great detail, but can be rather hard to read and interpret. Basically it states that the FTC requires any product manufacturer of a consumable product to list on their label exactly how much product the package contains. It needs to be listed by either unit of measure or weight or volume, depending on the product. Here are a few examples of random products from my house:
Cat treats: NET WT. 3 OZ (85g)
Screen Cleaner: NET WT. 4 Fl. Oz. (118ml)
Cleaning Wipes: 80 Wipes 6 x 6.5 in. (15.24 x 16.51 cm)
The cat treats are listed by the weight of the product. The screen cleaner spray is listed by liquid volume, which is specified by listing the ounces as "fluid" ounces. The wipes are listed as the total number of how many units are in the package, also including the size of each unit.
So for a candle, since everything is done by weight, you would want to list the contents of your candle by weight in ounces and then include the weight in grams in parentheses after it, just like on the cat treats example. Don't forget to deduct the weight of the jar or container itself, you only want to list the contents of the actual consumable product inside the container! If you have a digital scale with a tare feature, it is really easy.
You must also list your company name and contact info on the label. Here is exactly what the regulation says:
The best way to get examples of how to do your labels is to look at some from some of the large candle companies, like Yankee. I dug thru my candle box and found a few name brands to give you examples.
McCall's Country Canning lists theirs on the bottom, on their caution label. It says 16 oz. Classic Jar Candle. Burn Time 110 - 130 hrs.
Pilgrims Primitives lists theirs on the caution label also. It says "Approximate Net Wt. 3.75 oz."
L'Occitane lists theirs right on the label on the top of the tin. It says "100 g- Net Wt 3.5 OZ". Then on the bottom caution label it states "Around 20 hours of soft fragrancing for the home."
I also found a pillar candle made by Claire's Garden and it lists the size of the pillar instead of the weight. It says 4" x 4" Burns up to 90 hours.
If you have any questions please read over that FTC link thoroughly, and you can also try contacting them with any questions you're unsure of: http://www.ftc.gov/ftc/telephone.htm