I've been reading mixed recommendations on what is acceptable dress code in Thailand. I will start in the north in Bangkok and Chang Mai. I am sure to visit temples. I'll also be south and travel to beach resorts. Are shorts OK there? Is a knee length skirt OK for temples? I understand that my shoulders need to be covered. I can bring a scarf or I have a few dresses with short sleeves. Looking forward to advice from this knowledgeable community. Thanks!
For temples below the knee and shoulders covered is best. For walking around shorts and singlets are fine!!! Enjoy your time in Thailand, I'll be there in Jan as well :)
Most of the answers below should have you covered. Just as a cultural thing for the temples but you will most often see women wearing a black dress and loose white cotton shirt at the Wat. Absolutely no one would expect this of you but it's one way of being extra respectful, especially in the North and Northeast of Thailand.
You'll find that people will be very forgiving and understanding that you don't know the "rules" so don't worry too much. If you've got a summer dress and a scarf you'll be just fine.
For temples, depend on what kind of temples.
Royal temples in Bangkok and big cities such as Emerald Buddha temple, shorts are not allowed but they have sarongs for tourists. Some royal temples don't have that rules obviously, but better to wear longer.
For local temples, English speaking staffs and English sign boards are not available, they have less restricted rules.
However, knee length and covered shoulders dress are safe for every temple and you will be considered as the good tourist.
In general both in the cities and beaches, you can wear dress as you want. Thailand is tropical country and accustomed to tourists. Except specific rules in some places such as up-scale restaurants, and state offices.
Follow the advice of Julie "My recommendation would be to do as the local women do..." and all will be fine.
There are not dress codes, you'll only have to cover your legs in some temples but you can use a scarf or something like that.
Vest and Shorts! Vest and shorts all day long. The only time you have to worry, is when visiting temples and you have to cover up or wear specific things.
Some temples will not allow women to enter in if you are in shorts. Shorts at a temple is considered very disrespectful and some monks might stop you. Short shorts are a no no. Dresses just below the knees are ok. Above the knee you might have some issues. Make sure your dresses are not low cut and have at least some sleeves. If you are going to the beach your bathing suit with a wrap is fine.
Thailand is a wonderful country.
My recommendation would be to do as the local women do - shorts for the beach, not for the cities. I felt far more comfortable to "blend in" at least a little bit (giant height aside!).
Knee length skirts are absolutely fine for temples, and sleeves don't have to be long, they just have to exist :) Light scarves are fantastic as you can turn them into a sarong/wrap as necessary :)
Have a brilliant time, it's a fascinating country.