Two out of three Americans don't know what a healthy body mass index (BMI) is, a new national poll finds, despite the fact that knowing one's BMI score, along with a few other numbers, can tell people if they are at risk for a variety of health problems.

Researchers at The Ohio State University surveyed more than 2,000 adults from across the United States and asked them questions about BMI, for example, whether a person with a BMI of 24 is underweight or obese, or is normal weight.

Only 38 percent of the respondents answered correctly, that a BMI of 24 is considered normal weight. Sixty-two percent of people either responded with the wrong answer, or said they were not sure.

BMI is a number calculated from a person's weight and height, and provides a reliable indicator of body fatness and the risk for heart problems for most people. However, BMI does not paint a complete picture of health. For example, athletes with a lot of muscle mass might have a BMI that puts them in the "overweight" category, even though they are generally very healthy.

So, in addition to BMI, people should know four other numbers to get a good picture of their health: their blood pressure, cholesterol levels, blood sugar levels and the circumference of their waist, the researchers said.

"There really are five numbers everyone should know when it comes to heart health," said Dr. Martha Gulati, director of preventive cardiology and women's cardiovascular health at The Ohio State University Wexner Medical Center. "Once you learn those numbers, they can not only tell you how healthy you are today, but can help your doctor predict heart problems in the future," she said.  [Beyond Vegetables and Exercise: 5 Ways to be Heart Healthy]

Here are the five numbers every person should know. 

1. Your BMI

BMI compares a person's height to their weight. It is calculated by dividing a person's weight (measured in kilograms) by the square of their height (measured in meters). A BMI lower than 18.5 is underweight. Between 18.6 and 24.9 is considered normal. A BMI of 25 through 29.9 is overweight, and 30 or higher is considered obese. The CDC offers a BMI caclulator for determining your BMI.

"Knowing where you lie within that spectrum is really important, because sometimes people will be very accepting of their weight, thinking, 'Well, that number sounds reasonable.' But is it reasonable for their height?" Gulati said.

2. Your waist circumference

Your waist size is important because it's an indicator of your belly fat. People with a lot of this fat are at increased risk of heart disease and type 2 diabetes. The waist circumference at the level of belly button is another helpful measure when estimating who is at risk for heart disease. For women, waist circumference should measure less than 35 inches (89 centimeters), and for men, it should be less than 40 inches (102 cm).

3. Cholesterol

High blood cholesterol can lead to heart disease and stroke. Levels of LDL ("bad") cholesterol should be under 100 milligrams per deciliter (mg/dL). A healthy "total" cholesterol number is below 200 mg/dL.

4. Blood sugar

High levels of glucose in the blood can cause diabetes, which increases the risk for cardiovascular disease, and can lead to other problems, such as eye disease, kidney disease and nerve damage. A healthy blood sugar number is under 100 after not eating for eight hours (fasting blood sugar).

5. Blood pressure

Two numbers are used to measure blood pressure — the systolic pressure, when the heart beats, over the diastolic pressure, when the heart relaxes between beats. A normal blood pressure is under 120/80 millimeters of mercury (mmHg). About one-third of Americans have high blood pressure, also called hypertension. Simple lifestyle changes, such as reducing sodium in the diet, quitting smoking, and medication can help lower blood pressure.

Email Bahar Gholipour or follow her @alterwiredFollow us @LiveScience, Facebook & Google+. Original article on LiveScience.

Related on LiveScience and MNN:

This story was originally written for LiveScience and was republished with permission here. Copyright 2014 LiveScience, a TechMediaNetwork company.