A person with a large body frame is thought to have a larger overall skeletal frame, greater bone density, and more bone mass than a person with a small or medium bone structure. The size of a person's bone structure can be estimated by taking measurements of the size of the wrist and the width of the elbow. While ideal body weight is often calculated based on the body mass index (BMI), body frame size is an additional factor to consider when a person is determining a healthy weight for which to achieve.

The BMI is based solely on a person's weight in relation to his or her height and does not take into consideration that people have differing body frames. A person with a large body frame may have a higher BMI than that of a person with a smaller frame because the bone mass is greater. For this reason, some people choose to factor in the size of their body frame when determining if they are at a healthy weight.

Body frame size can be estimated in a variety of ways, the quickest of which is having a person wrap his or her thumb and longest finger around the wrist. If the two fingers do not touch, that person could have a large body frame while someone whose fingers overlap could be considered small framed. A somewhat more accurate body frame size can be estimated by taking actual measurements of the wrist.

Sex and height become factors when using wrist measurements to determine body frame size. If a woman under 5 feet 2 inches (about 155 cm) tall has a wrist over 5.75 inches (about 146 mm) around, then her body frame may be considered large, but a woman over 5 feet 5 inches (about 163 cm) tall might not be thought to have a large body frame unless her wrist was over 6.5 inches (about 165 mm) around. A man over 5 feet 5 inches (about 163 cm) tall with a large body frame would generally have a wrist circumference of over 7.5 inches (191 mm).

Another measurement that can help determine if a person has a large body frame is elbow width, which is taken by bending the elbow and holding the forearm up to form a 90-degree angle. On either side of the elbow, a protruding bone can be located and it is the distance between these bones that makes up the person's elbow width. A 5-foot (about 150 cm) tall woman with an elbow width of more than 2.5 inches (about 64 mm) is considered large framed, although a 6-foot (about 180 cm) tall woman would need to have an elbow width over 2.75 inches (about 70 mm) before she fell into the large range. Taking sex into consideration, a 6-foot (about 180 cm) tall man with an elbow width of over 3.125 inches (about 79 mm) may have a large frame.

It may be difficult for someone with a large body frame to achieve a weight that allows him or her to appear as skinny as someone with a small body frame. Due to this fact, it can be beneficial to use a person's body frame size in conjunction with the BMI to calculate a realistic ideal weight. Generally, a person with a large body frame can determine his or her healthy weight by using the BMI and then adding 10 percent to that number. This weight is generally a more achievable goal than the BMI weight alone for someone who has more bone mass than the average person.