Manhattan is the most expensive place in the U.S. for a wedding, according to the annual Real Weddings Study by TheKnot.com.

The average amount spent on weddings in Manhattan was $86,916, compared to $57,343 in Long Island, N.Y., or the $51,287 average spent in North or Central New Jersey. It cost couples an average of $48,449 in fourth-ranked Chicago, and the outer boroughs of New York City came in fifth with an average of $47,121 spent.

With an average of $25,306 spent in Hawaii, not a single isle destination ranked among the 25 most-expensive markets.

TheKnot.com found that the least expensive place to get married in 2013 was Idaho, where couples spent an average of $16,159.

Weddings in the top two markets are most likely to be formal, black-tie affairs, while Savannah, Ga. and Hawaii have the most casual weddings, at 41 percent and 38 percent, respectively, partly explaining the costliest market rankings.

Another reason is, according to TheKnot.com, that Hawaii brides have among the smallest numbers of wedding guests, 81 on average, compared with Nevada, at 63.

The online wedding site also reports that brides in Hawaii and Nevada are least likely to register for gifts, at 62 percent and 69 percent, respectively.