BMI Calculator
Calculate your adult Body Mass Index with WHO categories or the lower Asian cut-offs, plus the healthy weight range for your height.
Verified October 2026 · Sources: WHO; CDC adult BMI categories; WHO expert consultation, Lancet 2004; NICE NG246
Healthy range = 18.5 × height² to 24.9 × height²
BMI categories and weights at your height
| Category | BMI | Weight at 175.0 cm |
|---|---|---|
| Underweight | Below 18.5 | Below 56.7 kg |
| Healthy weight | 18.5 – 24.9 | 56.7 kg – 76.3 kg |
| Overweight (pre-obesity) ← you | 25 – 29.9 | 76.6 kg – 91.6 kg |
| Obesity class I | 30 – 34.9 | 91.9 kg – 106.9 kg |
| Obesity class II | 35 – 39.9 | 107.2 kg – 122.2 kg |
| Obesity class III | 40 and above | 122.5 kg and above |
What if my weight changed?
BMI at that weight: 26.1 — overweight (pre-obesity) (+0.0 kg from now).
- Weighing yourself in clothes and shoes, or at different times of day — weigh first thing in the morning for consistency.
- Using adult categories for children and teenagers — under 20 you need BMI-for-age percentiles.
- Reading a high BMI as 'unhealthy' if you are very muscular — check your waist or body fat too.
- Ignoring ethnicity — South Asian and East Asian adults face higher risk at BMIs of 23–25 that the WHO standard scale calls healthy.
- Using BMI during pregnancy — use your pre-pregnancy BMI instead.
- →If your BMI is outside the healthy range, a GP or doctor can check blood pressure, blood sugar and cholesterol — these matter more than the number alone.
- →Pair BMI with a waist measurement: keep your waist below half your height (NICE).
- →Use the Calorie Calculator to estimate how much to eat to reach a healthier weight at a safe pace.
- →Small, steady changes (about 0.5 kg or 1 lb a week) are more sustainable than crash diets.
This tool is for informational purposes only. Always verify results with a qualified professional.
What is the BMI Calculator?
Body Mass Index (BMI) is a simple screening number that compares your weight with your height: weight in kilograms divided by height in metres squared. The World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC) use it to classify adult weight status, because across large populations a higher BMI tracks with a higher risk of type 2 diabetes, heart disease and some cancers. This BMI calculator works in metric or imperial units, shows your category, the healthy weight range for your exact height, and how far you are from it.
For adults the standard WHO categories are: underweight below 18.5, healthy weight 18.5 to 24.9, overweight (pre-obesity) 25 to 29.9, and obesity 30 or above, split into class I (30–34.9), class II (35–39.9) and class III (40+). A WHO expert consultation published in The Lancet in 2004 found that many Asian populations have a higher risk of diabetes and cardiovascular disease at lower BMIs, and added public-health action points at 23, 27.5, 32.5 and 37.5. The UK's NICE guideline NG246 applies these lower thresholds (overweight from 23, obesity from 27.5) to people of South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean family background. Choose the Asian cut-offs option if that applies to you.
Worked example: an adult who is 175 cm tall and weighs 80 kg has a BMI of 80 ÷ (1.75 × 1.75) = 26.1. Under WHO cut-offs that is in the overweight range. The healthy BMI range of 18.5–24.9 at 175 cm works out to 56.7–76.3 kg, so this person is about 3.7 kg above the upper end. Under the Asian cut-offs, the same BMI of 26.1 sits in the 'overweight (increased risk)' band, and the healthy range tops out at BMI 22.9, or 70.1 kg. In imperial units the formula is 703 × weight in pounds ÷ height in inches squared — 180 lb at 5 ft 9 in gives a BMI of 26.6.
BMI has real limitations. It cannot tell muscle from fat, so muscular athletes can read as overweight; it does not show where fat is stored, and fat around the waist carries more risk than fat on the hips; and it is less reliable in older adults, who may have lost muscle, and during pregnancy. That is why this calculator also lets you add your waist measurement for a waist-to-height ratio — NICE recommends keeping your waist to less than half your height. Treat BMI as a starting point for a conversation with a health professional, not a verdict on your health.
BMI for children and teenagers works differently. Because body fat changes as children grow and differs between boys and girls, anyone aged 2 to 19 needs a BMI-for-age percentile from growth charts (the CDC charts in the US, or the WHO growth reference elsewhere) rather than the adult categories. If you enter an age under 20, this tool shows the raw BMI number but points you to those percentile charts instead of labelling it.
How to Use This Calculator
- 1Choose metric (kg, cm) or imperial (lb, ft/in) units — values convert automatically when you switch.
- 2Pick WHO standard cut-offs, or the Asian cut-offs if you are of South Asian, East Asian, Middle Eastern or Black African/Caribbean background.
- 3Enter your age, height and weight. Your BMI updates instantly as you type.
- 4Read your category, the healthy weight range for your height and how far you are from it.
- 5Optionally add your waist measurement to see your waist-to-height ratio, and use the 'what if' slider to see the BMI at a different weight.
- 6Copy the result to share with your doctor or keep for your records.