Many overweight and obese Americans don't realize they have a weight problem.
A recent survey by Harris Interactive, a market research firm, found that 30 percent of people classified as overweight thought they were just normal size.
Thirty-nine percent of the heaviest Americans, who make up the morbidly obese, just considered themselves as merely overweight.
Experts say the findings could be part of the reason obesity is getting worse in America. People are less likely to do something about their weight if they don't realize they have a problem.
Americans may have a skewed idea of "how fat is fat" because most adults are now overweight, bariatric physician Karen Evans at the Medi-Weightloss Clinic in Orlando, Fla., told the Orlando Sentinel.
"The perception problem may be the fact that more than 60 percent of Americans are overweight, but because you are around those people all the time, you think it's normal," said Evans.
Obesity is a leading cause of diabetes and heart disease.