BMI Calculator — Calculate Your Body Mass Index
Our free BMI calculator computes your Body Mass Index from your height and weight in either imperial (feet, inches, pounds) or metric (centimeters, kilograms) units. See your BMI value, category, healthy weight range, and estimated body fat percentage. Switch between units instantly — all values convert automatically.
This tool is for informational and educational purposes only. BMI is a screening tool, not a diagnostic measure. Always consult a qualified healthcare provider for health assessments and medical advice.
BMI Categories (WHO Standard)
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk (malnutrition, osteoporosis) |
| 18.5 – 24.9 | Normal weight | Lowest risk range |
| 25.0 – 29.9 | Overweight | Increased risk of metabolic conditions |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40.0 and above | Obese Class III | Extremely high risk |
How to Calculate BMI
Metric Formula
BMI = weight (kg) ÷ height (m)²
Example: A person who weighs 70 kg and is 1.75 m tall: BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.9. Result: Normal weight.
Imperial Formula
BMI = (weight (lbs) × 703) ÷ height (inches)²
Example: A person who weighs 154 lbs and is 5'9" (69 inches) tall: BMI = (154 × 703) ÷ (69)² = 108,262 ÷ 4,761 = 22.7. Result: Normal weight.
BMI by Height — Healthy Weight Ranges
This table shows the healthy weight range (BMI 18.5–24.9) for common heights:
| Height | Healthy Weight Range (Imperial) | Healthy Weight Range (Metric) |
|---|---|---|
| 5'0" (152 cm) | 97–128 lbs | 44–58 kg |
| 5'2" (157 cm) | 104–135 lbs | 47–61 kg |
| 5'4" (163 cm) | 110–144 lbs | 50–65 kg |
| 5'5" (165 cm) | 114–149 lbs | 52–68 kg |
| 5'6" (168 cm) | 118–154 lbs | 54–70 kg |
| 5'7" (170 cm) | 121–158 lbs | 55–72 kg |
| 5'8" (173 cm) | 125–163 lbs | 57–74 kg |
| 5'9" (175 cm) | 128–168 lbs | 58–76 kg |
| 5'10" (178 cm) | 132–173 lbs | 60–79 kg |
| 5'11" (180 cm) | 136–178 lbs | 62–81 kg |
| 6'0" (183 cm) | 140–183 lbs | 64–83 kg |
| 6'1" (185 cm) | 144–188 lbs | 65–86 kg |
| 6'2" (188 cm) | 148–194 lbs | 67–88 kg |
| 6'3" (191 cm) | 152–199 lbs | 69–90 kg |
Limitations of BMI
BMI is a widely used but imperfect tool. Understanding its limitations helps interpret your result more accurately:
| Limitation | Explanation | Who Is Affected |
|---|---|---|
| Muscle mass ignored | Muscle weighs more than fat. High BMI may mean high muscle, not high fat | Athletes, bodybuilders |
| Age not considered | Older adults tend to have more fat at the same BMI than younger adults | People over 60 |
| Sex differences | Women naturally carry more fat than men at the same BMI | Women, especially post-menopause |
| Ethnicity | Health risks occur at lower BMI in some Asian populations | Asian populations (WHO suggests lower thresholds) |
| Fat distribution | BMI does not show where fat is stored. Abdominal fat is more dangerous than hip fat | Apple vs pear body shapes |
| Short stature | BMI can overestimate fatness in shorter people | People under 5' |
| Tall stature | BMI may underestimate fatness in taller people | People over 6'3" |
Beyond BMI — Other Health Metrics
| Metric | What It Measures | Healthy Range | Better Than BMI For |
|---|---|---|---|
| Waist Circumference | Abdominal fat (most dangerous fat type) | Men < 40" / Women < 35" | Central obesity risk |
| Waist-to-Height Ratio (WHtR) | Abdominal fat relative to height | < 0.5 (keep waist less than half height) | Cardiovascular risk |
| Waist-to-Hip Ratio (WHR) | Fat distribution (apple vs pear) | Men < 0.9 / Women < 0.85 | Fat distribution |
| Body Fat % (DEXA) | Actual fat vs lean mass percentage | Men 10–20% / Women 18–28% (fitness) | Body composition accuracy |
| Visceral Fat Score | Fat around internal organs | Below 13 (varies by scale) | Metabolic disease risk |
BMI and Health Risks
Research consistently shows associations between BMI and various health conditions. Higher BMI is associated with increased risk of type 2 diabetes, cardiovascular disease, hypertension, sleep apnea, certain cancers, and joint problems. Lower BMI (underweight) is associated with nutritional deficiencies, osteoporosis, anemia, and immune system problems.
However, these are population-level associations. Individual health depends on many factors including fitness level, diet quality, sleep, stress, genetics, and metabolic health markers. A person at BMI 27 who exercises regularly and has healthy blood markers may be healthier than a sedentary person at BMI 22. Always discuss your health status with a qualified healthcare provider.
Frequently Asked Questions
What is a normal BMI for a woman?
The WHO uses the same BMI scale for adult men and women: 18.5–24.9 is considered normal weight. However, women naturally have higher body fat percentages than men at the same BMI. Some researchers suggest that optimal BMI may differ slightly between sexes, but the standard clinical thresholds remain 18.5–24.9 for all adults.
How much do I need to weigh for a healthy BMI?
Use the healthy weight range section of this calculator. Enter your height and the tool shows the weight range that corresponds to a BMI of 18.5–24.9 for your height. For example, at 5'8", a healthy weight is 125–163 lbs (57–74 kg).
Does BMI change with age?
The standard adult BMI scale (18.5–24.9) applies to adults 18 and older and does not change with age. However, the health implications of BMI do change with age — older adults naturally have more body fat at the same BMI, and some research suggests that slightly higher BMI (around 25–27) may be associated with better outcomes in older adults. For children and teens, BMI is interpreted using age- and sex-specific growth charts.
Is BMI 25 considered overweight?
Yes, according to WHO classification, a BMI of 25.0 or above is classified as overweight. However, this threshold is a statistical boundary, not a sudden health cliff. The health risk increase from BMI 24.9 to 25.0 is negligible. BMI is one data point — overall lifestyle, fitness, and metabolic health markers provide a more complete picture of health.
What is morbid obesity?
Morbid obesity, also called Class III obesity or severe obesity, refers to a BMI of 40 or above. At this level, obesity is associated with significantly increased risk of serious health conditions and reduced life expectancy. Class III obesity is typically the threshold used to consider bariatric surgery as a treatment option. The term "morbid" refers to the increased risk of serious disease, not a moral judgment.