Quick answer
What is a healthy BMI?
For adults, a BMI of 18.5 to 24.9 is classed as healthy weight, 25 to 29.9 as overweight and 30 or above as obesity (WHO). BMI is your weight in kilograms divided by your height in metres squared, so 70 kg at 1.75 m gives a BMI of 22.9. It is a quick screening number, not a diagnosis: it cannot tell muscle from fat, which is why pairing it with your waist size gives a better picture.
On this page
How to use the bmi calculator
- Choose metric or imperial.
- Enter your height and weight. Your BMI and category update as you type.
- Optional: add your waist measured at the midpoint between your lowest rib and hip bone. This adds your waist-to-height ratio, a better guide to belly fat.
- Check your healthy weight range for your height and how far you are from it.
What is body mass index (BMI)?
Body mass index compares your weight with your height to give a single number that screens for underweight, overweight and obesity. It was devised in the 1830s by the Belgian statistician Adolphe Quetelet, and doctors, insurers and public health agencies still use it because it is quick, free and, across large groups, tracks body fat and disease risk reasonably well.
It is a screening tool, not a diagnosis. A high BMI is a prompt to look closer, at waist size, blood pressure, blood sugar and fitness, not proof of a health problem.
How BMI is calculated
Metric formula
70 kg and 1.75 m: 70 ÷ (1.75 × 1.75) = 22.9
Imperial formula
154 lb and 5′9″ (69 in): 703 × 154 ÷ 4,761 = 22.7
BMI categories for adults
The WHO and CDC use the same categories for men and women aged 20 and over. The WHO splits underweight and obesity further to reflect rising risk.
| BMI | Category | What it means |
|---|---|---|
| Below 16 | Severe thinness | Serious risk; seek medical advice |
| 16.0–16.9 | Moderate thinness | Risk of nutrient deficiency and weakened immunity |
| 17.0–18.4 | Mild thinness | Underweight; risk of low bone density and anaemia |
| 18.5–24.9 | Healthy weight | Lowest risk of weight-related disease |
| 25.0–29.9 | Overweight | Increased risk, especially with a large waist |
| 30.0–34.9 | Obesity class I | High risk of type 2 diabetes, high blood pressure and heart disease |
| 35.0–39.9 | Obesity class II | Very high risk |
| 40 and above | Obesity class III | Extremely high risk |
Healthy weight range by height
These are the weights that give a BMI of 18.5 to 24.9. The calculator shows yours exactly.
| Height | Healthy weight (lb) | Healthy weight (kg) |
|---|---|---|
| 4′10″ (147 cm) | 89–119 lb | 40–54 kg |
| 5′0″ (152 cm) | 95–127 lb | 43–58 kg |
| 5′2″ (157 cm) | 101–136 lb | 46–62 kg |
| 5′4″ (163 cm) | 108–145 lb | 49–66 kg |
| 5′6″ (168 cm) | 115–154 lb | 52–70 kg |
| 5′8″ (173 cm) | 122–164 lb | 55–74 kg |
| 5′10″ (178 cm) | 129–174 lb | 58–79 kg |
| 6′0″ (183 cm) | 136–184 lb | 62–83 kg |
| 6′2″ (188 cm) | 144–194 lb | 65–88 kg |
| 6′4″ (193 cm) | 152–205 lb | 69–93 kg |
Looking for a single target inside the range? The ideal weight calculator compares four clinical formulas.
Limitations of BMI
- It can’t tell muscle from fat. Muscular people are often classed as overweight despite low body fat.
- It ignores where fat sits. Fat around the organs (visceral fat) is far riskier than fat under the skin. Waist-to-height ratio picks this up; BMI does not.
- It misses age-related muscle loss. Older adults can have a “healthy” BMI while carrying a high share of body fat.
- Risk differs by ethnicity. People of Asian heritage face higher cardiometabolic risk at lower BMIs, around 23 and above.
- It isn’t for children or pregnancy. Children need age-and-sex percentiles; pregnancy weight gain has its own guidance.
For a fuller picture, add your waist in the calculator above or estimate body composition with the body fat calculator.
Health risks outside the healthy range
Above the range
Excess body fat, especially around the waist, raises the risk of high blood pressure, type 2 diabetes, heart disease, stroke, sleep apnoea, fatty liver disease, osteoarthritis and several cancers. Losing even 5 to 10% of body weight measurably improves blood pressure, blood sugar and cholesterol.
Below the range
Being underweight is linked to nutrient deficiencies, anaemia, weaker immunity, low bone density and, in women, irregular periods and reduced fertility. If you are underweight without trying, see a doctor to rule out an underlying cause.
Frequently asked questions
Is BMI accurate for everyone?
BMI is a reasonable screening tool for most adults, but it is less accurate for very muscular people (it can label them overweight), older adults who have lost muscle, pregnant women and children. For these groups, waist size or a body fat estimate adds important context.
What is a healthy BMI for women and men?
The same categories apply to adult men and women: 18.5 to 24.9 is healthy weight. At the same BMI, women naturally carry more body fat than men, which is normal and already reflected in the ranges.
Are BMI ranges different for Asian populations?
Yes. People of South Asian, Chinese and other Asian backgrounds tend to have higher risk of type 2 diabetes and heart disease at lower BMIs. A WHO expert consultation suggested action points from about 23 (increased risk) and 27.5 (high risk), and several countries use these lower cut-offs.
What is a good waist-to-height ratio?
Keep your waist to less than half your height, a ratio under 0.5. From 0.5 to 0.6 indicates increased health risk from belly fat, and 0.6 or above high risk. It works the same for men and women and across most ethnic groups.
How can I lower my BMI?
Lose weight gradually with a moderate calorie deficit, plenty of protein and regular strength training, so most of the weight you lose is fat rather than muscle. The calorie deficit calculator gives you a daily target and a realistic date.
Can children use this BMI calculator?
No. It is for adults aged 20 and over. Children’s and teenagers’ BMI has to be compared against growth charts for their age and sex (BMI-for-age percentiles), which a doctor or a paediatric calculator can do.
What BMI is considered obese?
A BMI of 30 or above. The WHO splits it further into class I (30 to 34.9), class II (35 to 39.9) and class III (40 or above), with health risk rising at each step.
How often should I check my BMI?
Once a month is plenty. Adult height does not change and day-to-day weight swings of 1 to 2 kg are normal, so checking more often mostly measures water. Look at the trend over several months.
Sources
- World Health Organization. Obesity and overweight fact sheet.
- Centers for Disease Control and Prevention. Adult BMI categories.
- WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet, 2004.
- Ashwell M, et al. Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors. Obes Rev, 2012.
- Nuttall FQ. Body mass index: obesity, BMI, and health: a critical review. Nutr Today, 2015.
This calculator gives estimates for healthy adults and is for information only. It is not a diagnosis or a substitute for advice from a doctor or registered dietitian.