Anthropometry

Anthropometry involves measuring various body dimensions in large numbers of people and calculating their averages and distributions. Measurements include height, sitting height, eye level, arm length, hand size, leg length, and shoulder breadth. The field also includes recording body size and shape, including weight, circumferences, and skinfold thickness, using standardized landmarks and tools.

A term often used in this field is percentile. The "sitting height of a 5th-percentile woman" means the measurement of the person who would be fifth from the front if 100 people in the same group were lined up from smallest to largest. These statistics make it easy to see the spread from the smallest to the largest people.

Most objects that come into direct contact with the human body are designed using these data. Common examples include chair seat height, desk height, workbench height, car seat position, tool handle thickness, and clothing and shoe sizes. "Standard desk height" and "standard chair height" also come from using statistics to identify a range that fits as many people as reasonably possible.

You can read more about everyday applications in Ergonomics, Chair and sitting ergonomics, and Workstation ergonomics.

Height and limb length vary considerably between individuals. A single standard size therefore fits people with near-average body proportions best, and may become less comfortable the farther someone falls outside that range. People who are very short may find their shoulders raised at a standard desk, while tall people often find that a low chair brings their knees up high and leaves their lower back rounded.

So if your desk and chair feel uncomfortable, rather than blaming yourself and wondering, "Is my posture bad?", it helps to first ask, "Does this setup fit my dimensions?" Simply adjusting chair height, a footrest, monitor height, and desk height to suit your body often makes things much more comfortable. Even a posture well suited to your body can cause stiffness if held for a long time, so it is also important to get into the habit of changing positions and moving from time to time. You can read more about this perspective in No single ideal posture.

Many people use a tape measure to measure their own waist circumference or arm length. Keeping a few things in mind can make those measurements more dependable.

• Use the same landmarks. Waist circumference varies depending on where you place the tape, so measure at the same location each time.
• Keep your posture and breathing consistent. Measure while standing upright after breathing out comfortably, and avoid pulling the tape too tight.
• Use the same tool at a similar time of day. Keeping conditions consistent, such as measuring in the morning before eating, makes it easier to compare changes in your body.
• Measure repeatedly and look at the trend. The trend in measurements collected over several weeks is more meaningful than a single measurement.
• Get help if a measurement is difficult to take alone. For areas you cannot easily see yourself, such as your back, having someone else take the measurement is more accurate.

Measurements are not the body itself, but observations obtained through a defined procedure. Even for the same person, they may vary slightly depending on who takes the measurement, the landmarks used, and the tool. Getting the same value repeatedly is different from accurately measuring what you intend to measure. For example, waist circumference measures the distance around the abdomen, while skinfold thickness measures the thickness of fat beneath the skin. Neither gives a complete picture of internal body fat or total muscle mass, so it is more helpful to interpret them alongside other measurements, such as Body composition analysis or Body fat percentage.