Unfortunately (unlike shoe sizing) there is no universal regulation for womens clothing sizes. A size 14 at Kmart WILL be a size 4 at a high end expensive department store...there are sometimes reasons for this and sometimes it's just up to the manufacturer. Generally within any one brand I would guess that the sizing is fairly evenly spaced (each size is an equal amount larger or smaller than any other) but between designers and manufacturers no such agreement.
Back to your question. More difficult is the clothing style/dress style. Certain dresses are more forgiving in certain uh, "areas" allowing for you to gain a good 15 pounds in the rear, but because it's an A-line dress, you'd still be able to wear it without much notice....now on contrast, take something spandex from neck to hem and even a pound or two will make a tremendous difference in wearability.
Can you see why this is a tough question to answer?
I've always wondered why women don't get together, boycott clothing manufacturing and insist that there be universal sizes. For example a size 8 at walmart would be exactly the same measurements at a size 8 from the lands end catalog - but then again, the style of the garment and the fact that it is to the manufacturers advantage to make a wealthy woman feel smaller in a more expensive dress that reads a size 2, when a less fortunate kmart shopper in a very similar dress looks into it and reads a size 12. Go figure.
Years ago, sizing was much smaller...womens bodys are physically larger now (each generation is slightly taller/larger than the previous - look at your parents for example) and companies know this...and they know that no one wants to buy a larger size pant if they don't have to...it's a tricky world out there and please try to remember, you are not a number -
Also, don't go by your old clothing either - sizing practices change and reflect the wishes of the buying public too - know that 10 years ago, what was once a size 8 at THE GAP is the same pant, but NOW it is called a size 6...pretty tricky huh?
go by how your body feels...if you feel better, your clothing will eventually fit better because you will treat yourself/feed yourself better (the general gist of it).
And, are you in a hurry? Hope not. Some folks lose very slowly but steadily, some quickly in spurts stops and starts.
A dress is a size. I do not believe there is a standard, "drop 10 pounds and you drop a dress size" mantra in most cases. Generally, just losing the weight should be the reward in itself - think how much healthier you'll be (not just how much smaller).
...oh gosh - don't even mention JEANS!!!
N