Throughout her career, Mansfield was compared by the media to the reigning sex symbol of the period, Marilyn Monroe. 20th Century Fox groomed her, as well as Sheree North, to substitute Monroe, their resident "blonde bombshell", while Universal Pictures launched Van Doren as their substitute. The studio launched Mansfield, their new bombshell, with a grand 40-day tour of England and Europe from September 25 to November 6, 1957. She adopted Monroe's vocal mannerisms instead of her original husky voice and Texan speech, performed in two plays that were based on Marilyn Monroe vehicles -- Bus Stop and Gentlemen Prefer Blondes, and her role in The Wayward Bus was strongly influenced by Monroe's character in Bus Stop.
Other studios also tried to find their own version of Monroe. Columbia Pictures tried it with Cleo Moore, Warner Bros. with Carroll Baker, Paramount Pictures with Anita Ekberg, and Metro-Goldwyn-Mayer with Barbara Lang, while Diana Dors was dubbed as England's answer to Mansfield. Jacqueline Susann wrote, "When one studio has a Marilyn Monroe, every other studio is hiring Jayne Mansfield and Mamie Van Doren." The crowd of contenders also included Diana Dors, Sheree North, Kim Novak, Cleo Moore, Joi Lansing, Beverly Michaels, Barbara Nichols and Greta Thyssen, and even two brunettes -- Elizabeth Taylor and Jane Russell. Mamie Van Doren, Diana Dors and Kim Novak also acted in various productions of Gentlemen Prefer Blondes. But, even when Mansfield's film roles were drying up, she was widely considered to be Monroe's primary rival, and she considered Mamie Van Doren as her professional nemesis. At one point, Monroe, Mansfield and Mamie came to be known as "The Three M's."
Because of her striking figure, newspapers in the 1950s routinely published her body measurements, which once led to evangelist Billy Graham exclaiming, "This country knows more about Jayne Mansfield's statistics than the Second Commandment." Mansfield claimed a 41-inch bust line and a 22-inch waist when she made her Broadway debut in 1955, though some scholars dispute those figures. She came to be known as "the Cleavage Queen" and "the Queen of Sex and Bosom." Mansfield's breasts fluctuated in size, it was said, from her pregnancies and nursing her five children. Her smallest measurement was 40D (102 cm), which was constant throughout the 1950s, and her largest was 46DD (117 cm), measured by the press in 1967. According to Playboy, her vital statistics were 40D-21-36 (102-53-91 cm) on her 5'6" (1.68 m) frame. According to her autopsy report, she was 5'8" (1.73 m).
It has been claimed that her bosom was a major force behind the development of the 1950s brassieres, including the "Whirlpool bra", Cuties, the "Shutter bra", the "Action bra", latex pads, cleavage-revealing designs and uplift outline. R. L. Rutsky and Bill Osgerby have claimed that it was Mansfield, along with Marilyn Monroe and Brigitte Bardot, who made the bikini popular. Drawing on the Freudian concept of fetishism, British science fiction writer and socio-cultural commentator J. G. Ballard commented that Mae West, Mansfield and Monroe's breasts "loomed across the horizon of popular consciousness." But, as the 1960s approached, according to Dave Kehr, the anatomy that had made her a star turned her into a joke. In this decade, the female body ideal shifted to appreciate the slim waif-like features popularized by supermodel Twiggy, actress Audrey Hepburn and other, demarcating the demise of the busty blonde bombshells.