When looking for a gift and the size is of question I have taken to the one size fits all approach. I go for hats, gloves, scarves, and socks. Admittedly these gifts are not as fun as some others but what do you do when you are unsure of the size and you want to avoid embarrassment on the person you are bestowing a gift to or giving them a chore or task by having to make a return? I have learned that some articles of clothing can be given to a range of sizes. Maxi dresses are one of these items. Basically they come in small, medium and large sizes and it is easy to put a person in one of those categories.
One item I have a bit of trouble sizing are swim suits, I would not pick that out for a lady, every woman has preferences in suits and it is hard to guess the swim suit size. But on the other hand plus size summer dresses are something that would be easier to guess a size for. When giving gifts where size is important to know do a little investigation, it requires planning ahead but it is worth it in the end.