Approximately 63% of consumers are unable to accurately estimate the number of calories they should consume

Most people don't know their own number.

That is, they don't know how many calories they should consume in a day to maintain their current weight, a nationally representative online survey of 1,024 people shows.

In fact, 63% can't accurately estimate the number, 25% won't even venture a guess and only 12% can nail it.

"People need to know their numbers," says registered dietitian Wendy Reinhardt Kapsak of the International Food Information Council Foundation, an education group supported by the food, beverage and agricultural industries. The foundation paid for the survey.

Having some frame of reference could be an important first step in tackling your weight, she says. "There is confusion on all sides of the calorie equation. People don't know how many calories they should consume in a day, and even more are unclear how many they burn."

There's a reason for this: Calorie requirements are unique to each person, and how many you need depends on your gender, age, height and physical activity level, Reinhardt Kapsak says. "Adult calorie requirements can range from 1,400 to 1,600 a day for a small sedentary woman to 4,000 or more calories a day for a highly trained endurance athlete."

Your output must equal your input or you'll gain weight, but 58% of respondents say they don't try to balance the calories they consume with those they burn, she says.

These findings don't surprise Dawn Jackson Blatner, a registered dietitian in Chicago and a nutrition blogger at dietchallenge.usatoday.com. She has noticed her patients don't know much about the topic. "Nobody knows how many calories they should be eating, nobody knows how many they are eating, and nobody knows how many calories are in foods," she says. "I would say it's beyond calorie-confused. It's calorie-oblivious."

She says some simple calorie know-how would go a long way toward helping people lose or maintain their weight. "I don't teach people calorie counting. I teach them calorie consciousness."

Other survey findings:

•70% of people say they are concerned about their weight.

•54% say they are trying to lose weight; 23% are trying to maintain; 19% are doing nothing; and 4% are trying to gain weight.

•Of those trying to lose or maintain weight, most say they are changing the amount and types of food they eat and doing physical activity; 65% say weight loss is the main reason they're eating better.

•Among roadblocks people give for not sticking with weight loss attempts: lack of willpower, lack of time, not seeing results quickly and boredom.

•77% don't meet the government's guidelines of 2½ hours of moderate-intensity physical activity a week.