A Mormon wedding is restricted to only practicing Mormons. The wedding is usually at the temple which is a religious and solemn affair that is formal. After the wedding ceremony, a public reception will take place. Before the reception day, get a brief outline from a Mormon friend as to what to wear for the ceremony. If the bride or groom is your friend, talk to them and find out about the dress code. For non-Mormon guests, the dress code does not necessarily apply in the same way as to a Mormon. But, out of courtesy and respect for their beliefs, avoid wearing inappropriate attire.
For men, wearing a suit is a good idea. But if you feel it is too formal, a blazer can be worn with a collared shirt. This can be teamed up with khaki. Your attire is sure to complement the occasion. Wearing a collared shirt without a blazer may seem too informal and too casual. But, you can always take off the blazer. Or, it can be something between a business casual and a suit. Button-up collared shirt with a slack can be worn. A loose fitting casual pant with a nice sweater will be more comfortable as well.
In a Mormon wedding ceremony, only the groom and the couple’s close relatives, wear a tie. So avoid wearing a tie. Avoid wearing pleated pants. Tuxedo is not necessary. This could add variety to the crowd than appearing like a uniform.
For women, the skirt should be at least ankle length. Avoid wearing a short skirt. Wear a dress that has sleeves. The dress must not be too revealing. No spaghetti straps. No bare shoulders. No low cut tops. It is a good idea to bring a wrap, so that it can be used to cover the shoulders. Or it can be draped if the dress is too tight or revealing. This will add to your comfort level. The general rule to remember is not too much skin. The dress has to be modest. Choose something which is classy, elegant and sophisticated.
As seen above, most are just formal wear with a religious fervor than a strict code. It is always good to talk to the person concerned to find out what is planned or expected of the guests. Also, planning it with someone else, who is also attending, will help you not to be caught unawares and totally dressed out of place.