Body mass index

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Body mass index (BMI) is a widely used measure to estimate body fat based on an individual's height and weight. It serves as a simple screening tool to categorize individuals as underweight, normal weight, overweight, or obese.

Calculation of BMI

BMI is calculated using either the metric or imperial system.

Metric formula

BMI = weight (kg) / height (m)2

Since height is often measured in centimeters, it should be converted to meters before using the formula.

Example:

  • Weight = 68 kg
  • Height = 165 cm = 1.65 m
  • Calculation: 68 / (1.65)2 = 24.98

Imperial formula

BMI = (weight (lb) / height (in)2) x 703

Example:

  • Weight = 150 lbs
  • Height = 5'5" = 65 in
  • Calculation: (150 / (65)2) x 703 = 24.96
BMI chart overview

Interpretation of BMI for Adults

For adults aged 20 years and older, BMI is interpreted using standard weight status categories. It helps estimate health risks related to excess body fat, such as:

Limitations of BMI

While BMI is useful for general population screening, it has limitations:

  • May overestimate body fat in individuals with a muscular build (e.g., athletes)
  • May underestimate body fat in elderly individuals and others with low muscle mass

Adult BMI Categories

  • Below 18.5: Underweight
  • 18.5–24.9: Normal weight
  • 25.0–29.9: Overweight
  • 30.0–34.9: Class I Obesity (Mild)
  • 35.0–39.9: Class II Obesity (Moderate)
  • 40.0 and above: Class III Obesity (Severe or Morbid)

BMI for Children and Teens

Although BMI is calculated the same way for children and teens as for adults, its interpretation differs. Age- and sex-specific percentiles are used to account for:

  • Changes in body fat with age
  • Differences in body fat between boys and girls

These percentiles are based on growth charts and are used to determine whether a child or teen is underweight, normal weight, overweight, or obese.

Adult Body Mass Index Chart

WEIGHT 4'8" 4'9" 4'10" 4'11" 5'0" 5'1" 5'2" 5'3" 5'4" 5'5" 5'6" 5'7" 5'8" 5'9" 5'10" 5'11" 6'0" 6'1" 6'2" 6'3" 6'4" 6'5"
lbs (kg) 142cm 147.32 149.86 152.4 154.94 157.48 160.02 162.56 165.1 167.64 170.18 172.72 175.26 177.8 180.34 182.88 185.42 187.96 190.5 193.04 195.58
260 (117.9) 58 56 54 53 51 49 48 46 45 43 42 41 40 38 37 36 35 34 33 32 32 31
255 (115.7) 57 55 53 51 50 48 47 45 44 42 41 40 39 38 37 36 35 34 33 32 31 30
250 (113.4) 56 54 52 50 49 47 46 44 43 42 40 39 38 37 36 35 34 33 32 31 30 30
245 (111.1) 55 53 51 49 48 46 45 43 42 41 40 38 37 36 35 34 33 32 31 31 30 29
240 (108.9) 54 52 50 48 47 45 44 43 41 40 39 38 36 35 34 33 33 32 31 30 29 28
235 (106.6) 53 51 49 47 46 44 43 42 40 39 38 37 36 35 34 33 32 31 30 29 29 28
230 (104.3) 52 50 48 46 45 43 42 41 39 38 37 36 35 34 33 32 31 30 30 29 28 27
225 (102.1) 50 49 47 45 44 43 41 40 39 37 36 35 34 33 32 31 31 30 29 28 27 27
220 (99.8) 49 48 46 44 43 42 40 39 38 37 36 34 33 32 32 31 30 29 28 27 27 26
215 (97.5) 48 47 45 43 42 41 39 38 37 36 35 34 33 32 31 30 29 28 28 27 26 25
210 (95.3) 47 45 44 42 41 40 38 37 36 35 34 33 32 31 30 29 28 28 27 26 26 25
205 (93.0) 46 44 43 41 40 39 37 36 35 34 33 32 31 30 29 29 28 27 26 26 25 24
200 (90.7) 45 43 42 40 39 38 37 35 34 33 32 31 30 30 29 28 27 26 26 25 24 24
195 (88.5) 44 42 41 39 38 37 36 35 33 32 31 31 30 29 28 27 26 26 25 24 24 23
190 (86.2) 43 41 40 38 37 36 35 34 33 32 31 30 29 28 27 26 26 25 24 24 23 23
185 (83.9) 41 40 39 37 36 35 34 33 32 31 30 29 28 27 27 26 25 24 24 23 23 22
180 (81.6) 40 39 38 36 35 34 33 32 31 30 29 28 27 27 26 25 24 24 23 22 22 21
175 (79.4) 39 38 37 35 34 33 32 31 30 29 28 27 27 26 25 24 24 23 22 22 21 21
170 (77.1) 38 37 36 34 33 32 31 30 29 28 27 27 26 25 24 24 23 22 22 21 21 20
165 (74.8) 37 36 34 33 32 31 30 29 28 27 27 26 25 24 24 23 22 22 21 21 20 20
160 (72.6) 36 35 33 32 31 30 29 28 27 27 26 25 24 24 23 22 22 21 21 20 19 19
155 (70.3) 35 34 32 31 30 29 28 27 27 26 25 24 24 23 22 22 21 20 20 19 19 18
150 (68.0) 34 32 31 30 29 28 27 27 26 25 24 23 23 22 22 21 20 20 19 19 18 18
145 (65.8) 33 31 30 29 28 27 27 26 25 24 23 23 22 21 21 20 20 19 19 18 18 17
140 (63.5) 31 30 29 28 27 26 26 25 24 23 23 22 21 21 20 20 19 18 18 17 17 17
135 (61.2) 30 29 28 27 26 26 25 24 23 22 22 21 21 20 19 19 18 18 17 17 16 16
130 (59.0) 29 28 27 26 25 25 24 23 22 22 21 20 20 19 19 18 18 17 17 16 16 15
125 (56.7) 28 27 26 25 24 24 23 22 21 21 20 20 19 18 18 17 17 16 16 16 15 15
120 (54.4) 27 26 25 24 23 23 22 21 21 20 19 19 18 18 17 17 16 16 15 15 15 14
115 (52.2) 26 25 24 23 22 22 21 20 20 19 19 18 17 17 16 16 16 15 15 14 14 14
110 (49.9) 25 24 23 22 21 21 20 19 19 18 18 17 17 16 16 15 15 15 14 14 13 13
105 (47.6) 24 23 22 21 21 20 19 19 18 17 17 16 16 16 15 15 14 14 13 13 13 12
100 (45.4) 22 22 21 20 20 19 18 18 17 17 16 16 15 15 14 14 14 13 13 12 12 12
95 (43.1) 21 21 20 19 19 18 17 17 16 16 15 15 14 14 14 13 13 13 12 12 12 11
90 (40.8) 20 19 19 18 18 17 16 16 15 15 15 14 14 13 13 13 12 12 12 11 11 11
85 (38.6) 19 18 18 17 17 16 16 15 15 14 14 13 13 13 12 12 12 11 11 11 10 10
80 (36.3) 18 17 17 16 16 15 15 14 14 13 13 13 12 12 11 11 11 11 10 10 10 9

Source: BRFSS survey data from CDC

Limitations of BMI

Although BMI is widely used as a screening tool for body fat, it has some limitations. BMI does not distinguish between fat and muscle, which can result in an inaccurate classification of body fat in athletes and individuals with a muscular build. Additionally, BMI does not take into account body composition or distribution of body fat, which can impact health outcomes. For example, visceral fat, which is located deep in the abdomen and surrounds organs, is associated with an increased risk of metabolic disorders such as Type 2 Diabetes and cardiovascular disease.

Usefulness of BMI

Despite its limitations, BMI remains a useful tool for population-level screening for overweight and obesity. It can be used to estimate the prevalence of overweight and obesity in a population and to track changes over time. BMI can also be used as a starting point for discussions between healthcare providers and patients about weight-related health risks and the need for lifestyle changes.

Distribution of body weight by percentage distribution adults - 2012

State: Underweight (bmi 12.0-18.4) Normal Weight (bmi 18.5-24.9) Overweight (bmi 25.0-29.9) Obese (bmi 30.0 - 99.8)
Nationwide (States, DC, and Territories) 1.8 34.2 35.8 28.1
Nationwide (States and DC) 1.8 34.2 35.8 27.6
Alabama 1.7 30.6 34.8 33.0
Alaska 0.9 34.4 39.1 25.7
Arizona 2.3 35.7 36.0 26.0
Arkansas 1.8 29.5 34.2 34.5
California 1.9 37.8 35.3 25.0
Colorado 2.3 42.0 35.2 20.5
Connecticut 1.7 36.1 36.7 25.6
Delaware 1.5 32.5 39.1 26.9
District of Columbia 2.2 46.0 30.0 21.9
Florida 1.5 36.4 36.9 25.2
Georgia 2.0 33.3 35.5 29.1
Guam 2.9 35.6 32.4 29.1
Hawaii 2.7 41.2 32.5 23.6
Idaho 1.8 35.7 35.8 26.8
Illinois 2.2 33.8 35.8 28.1
Indiana 1.7 32.8 34.1 31.4
Iowa 1.8 33.5 34.3 30.4
Kansas 2.0 32.4 35.7 29.9
Kentucky 2.0 31.1 35.6 31.3
Louisiana 1.9 28.5 34.8 34.7
Maine 1.6 34.3 35.8 28.4
Maryland 2.0 34.2 36.2 27.6
Massachusetts 2.1 39.2 35.9 22.9
Michigan 1.6 32.8 34.6 31.1
Minnesota 1.6 35.4 37.3 25.7
Mississippi 1.8 29.3 34.3 34.6
Missouri 1.9 32.4 36.2 29.6
Montana 1.5 37.1 37.0 24.3
Nebraska 1.7 33.3 36.4 28.6
Nevada 2.7 34.8 36.3 26.2
New Hampshire 1.4 36.5 34.8 27.3
New Jersey 1.9 36.5 37.0 24.6
New Mexico 2.2 35.0 35.7 27.1
New York 2.6 36.9 37.0 23.6
North Carolina 1.8 32.4 36.3 29.6
North Dakota 1.8 32.0 36.6 29.7
Ohio 1.7 33.0 35.2 30.1
Oklahoma 1.8 30.4 35.6 32.2
Oregon 1.7 37.2 33.8 27.3
Pennsylvania 1.7 33.3 35.9 29.1
Puerto Rico 2.1 31.7 37.8 28.4
Rhode Island 1.6 35.5 37.2 25.7
South Carolina 1.5 32.4 34.5 31.6
South Dakota 1.5 32.4 37.9 28.1
Tennessee 2.0 32.7 34.2 31.1
Texas 1.8 33.2 35.9 29.2
Utah 1.8 40.4 33.5 24.3
Vermont 1.7 38.0 36.6 23.7
Virginia 2.0 34.4 36.2 27.4
Washington 1.8 36.0 35.4 26.8
West Virginia 1.7 30.0 34.5 33.8
Wisconsin 1.8 31.8 36.8 29.7
Wyoming 1.5 35.1 38.7 24.6

Children BMI calculator

The formulas used in children are different as their weight is based on growth charts and do not correspond to adult BMI scale numbers. Use an online childhood BMI calculators below.

BMI Calculators

See also

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