I would say the 3X fits like a size 16W
581409
Runs SMALL!  I had read the previous reviews so I ordered a size larger than I normally would and it is still quite snug.  I would say the 3X fits like a size 16W.  Otherwise, the quality is very nice for a costume at this price.
2048258
I wear a 26 and the 3X is just fine. The cloth is a little on the thin side, which is good for warm climates. It is very fragrant, almost vinegary, so somewhat off-putting when you open the package. Definitely gentle washing and lay flat drying, with the material being delicate.
3866708
If your sizes were true, the triple x would have fit me.  As it was, I gave it to my granddaughter who wears a size 2.  Your company really needs to get the sizes accurate.  This is the fourth piece of clothing than ran way too small.
1224241
So I'm a size 16, wearing a size 36I bra, and i ordered a. 6x. It fits...i *probably* could have gone down a size, but in no fantasy land am i a 5x.

I like it, although I wish it came with built in garters, or at least loops to attach them.
1338273
Im a size 14 and i got the 3x based on the reviews. Fit perfectly. Its below the knee.
2761500
I love it!  I probably could have gotten away with the 3X but I'm happy with what I have so I'm keeping it.  The fabric is soft and not too clingy, it also flows nicely.  As you can see in the pictures it fits me a little loose.  This particular color isn't sheer at all so no undershirt required!  Probably will buy more of these!
Here are my measurements to give you a good idea of the fit
Height: 5' 2.5''
Bust: 48.5"
Shoulder Width: 19"
Torso Length: 28" shoulder to hip
Waist: 49.5"
Hip: 48.5"
399064
Nice Shirt but, a 3X fits like a 2X....Returned.
587140
I wear extra large so decided to buy a 3x..yet its somewhat small..yet pretty
232988
I wear a 3x and they would of fit a 5x easy
4324077
My daughter wears a size 18 (she is a 43DD) and the 3XL fit her perfectly. She loves this suit!
1488538
I ordered a 3X (well my husband did) and it's more like a 1X.
2195218
Good quality. Very nice but size is way off. I normally wear a 16w and I am 5ft 9 in,  so I bought a 3X and it was too tight and short. I couldn't wear it.
1494477
The top fits just fine. The bottoms are EASILY three sizes too small. I have no idea how they could be considered 3X.
4341912
These run slightly small.  A 3X fits like a 2X,  It's as I expected because I have purchased before.
2100585
3X has always been a safe size for me to order. It's typically a size that gives me extra room. I ordered that size in case I wanted to layer over a sweatshirt, but being the pear-shape that I am it is a bit tight. I kept it because it's the largest they had and I NEEDED a rain jacket, but I wish it had more room in the hips. It fits everywhere else fine/roomy, but on the hips. When slick fabric is tight it tends to ride up.
1624225
I plan on returning the shirt, it does not fit me like most 3X's
1626495
I'm a size 22/24 & ordered a 3-4x and it fit pretty good. Its so smooth it won't stay tied but other then that its flattering and I have room.