WHO BMI Classification for Adults
The World Health Organization (WHO) recommends the following BMI categories for adults aged 18 and above. These classifications are used globally for epidemiological studies and clinical assessments.
| Classification | BMI Range (kg/m²) | Health Risk |
|---|---|---|
Severe Thinness | < 16 | Very High |
Moderate Thinness | 16 – 17 | High |
Mild Thinness | 17 – 18.5 | Moderate |
Normal Weight ✓ | 18.5 – 25 | Low |
Overweight | 25 – 30 | Moderate |
Obese Class I | 30 – 35 | High |
Obese Class II | 35 – 40 | Very High |
Obese Class III | > 40 | Extremely High |
Source: World Health Organization (WHO), Global Database on Body Mass Index.
BMI Color Scale — At a Glance
What is Body Mass Index (BMI)?
Body Mass Index (BMI) is a numerical value derived from a person's weight and height. It is widely used as a screening tool to categorize individuals into health weight categories — underweight, normal weight, overweight, and obese. BMI was developed by Belgian mathematician Adolphe Quetelet in the 1830s and was later adopted by the World Health Organization as a global health indicator.
The formula is straightforward: BMI = weight (kg) ÷ height² (m²). For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the Normal Weight category.
Limitations of BMI
While BMI is a useful population-level tool, it has important limitations at the individual level:
- Muscle vs. Fat: BMI cannot distinguish between lean muscle mass and body fat. Athletes and bodybuilders may have high BMI values but very low body fat percentages.
- Age Differences: Older adults tend to have more body fat than younger people at the same BMI. The healthy BMI range may be slightly different for seniors.
- Ethnic Variations: Asian populations may have higher health risks at lower BMI values compared to European populations. Some health organizations recommend a lower threshold of 23 for Asian adults.
- Fat Distribution: BMI doesn't capture where fat is stored. Abdominal (visceral) fat poses greater health risks than fat stored elsewhere.
BMI Prime
BMI Prime is the ratio of your BMI to the upper limit of the normal BMI range (25). A value of 1.0 means you are at the upper edge of the normal range. Values below 1.0 indicate normal or underweight; values above 1.0 indicate overweight. It provides a quick way to see how far you are from the ideal upper boundary.
Tips to Achieve & Maintain a Healthy BMI
Eat a Balanced Diet
Focus on whole foods: vegetables, fruits, lean proteins, and whole grains. Limit ultra-processed foods, sugary drinks, and excessive saturated fats.
Exercise Regularly
WHO recommends at least 150–300 minutes of moderate-intensity aerobic activity per week for adults, plus muscle-strengthening on 2+ days/week.
Stay Hydrated
Drink 2–3 litres of water daily. Proper hydration supports metabolism, digestion, and can help manage appetite and weight.
Prioritize Sleep
Adults need 7–9 hours of quality sleep per night. Poor sleep is directly linked to weight gain and metabolic disorders.
Manage Stress
Chronic stress raises cortisol levels, promoting fat storage (especially belly fat). Practice mindfulness, yoga, or other stress-reduction techniques.
Regular Checkups
Don't rely on BMI alone. Get regular health checkups including blood pressure, blood sugar, and cholesterol — especially if your BMI is outside the normal range.
Healthy Weight Range by Height
The table below shows the healthy weight range (BMI 18.5–25) for common heights in both metric and imperial units.
| Height (cm) | Height (ft/in) | Min Weight (kg) | Max Weight (kg) | Min–Max (lbs) |
|---|---|---|---|---|
| 150 cm | 4′11″ | 41.6 kg | 56.3 kg | 92–124 lbs |
| 155 cm | 5′1″ | 44.4 kg | 60.1 kg | 98–133 lbs |
| 160 cm | 5′3″ | 47.4 kg | 64 kg | 105–141 lbs |
| 165 cm | 5′5″ | 50.3 kg | 68 kg | 111–150 lbs |
| 170 cm | 5′7″ | 53.4 kg | 72.2 kg | 118–159 lbs |
| 175 cm | 5′9″ | 56.7 kg | 76.6 kg | 125–169 lbs |
| 180 cm | 5′11″ | 59.9 kg | 81 kg | 132–179 lbs |
| 185 cm | 6′1″ | 63.3 kg | 85.6 kg | 140–189 lbs |
| 190 cm | 6′3″ | 66.8 kg | 90.3 kg | 147–199 lbs |
Healthy weight range calculated for BMI 18.5–25 (WHO Normal Weight category).