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What your BMI means
Body mass index (BMI) is your weight in kilograms divided by your height in metres squared. It's a quick screening measure for adults used by the CDC, the NHS and NICE — a starting point, not a diagnosis.
| BMI | Most adults | South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background |
|---|---|---|
| Underweight | Under 18.5 | Under 18.5 |
| Healthy weight | 18.5 to 24.9 | 18.5 to 22.9 |
| Overweight | 25 to 29.9 | 23 to 27.4 |
| Obesity (class 1) | 30 to 34.9 | 27.5 to 32.4 |
| Obesity (class 2) | 35 to 39.9 | 32.5 to 37.4 |
| Obesity (class 3) | 40 or more | 37.5 or more |
Is BMI different for women and men?
No. Women and men use the same formula and the same categories. The CDC says that for adults aged 20 and over, BMI categories are based on BMI "regardless of age, sex, or race". What can differ is how a clinician reads it alongside your waist size, health and background. BMI isn't used to judge weight during pregnancy; your midwife, obstetrician or doctor uses other measures.
Does age change your BMI result?
For adults, the categories stay the same whatever your age. NICE advises interpreting BMI with caution from age 65, taking into account other health conditions and the possible protective effect of a slightly higher BMI in older people. Children and teenagers are different: their BMI is compared with others of the same age and sex as a percentile, using the CDC Child and Teen BMI Calculator for ages 2 to 19.
BMI chart: healthy weight for your height
The healthy-weight range for most adults (BMI 18.5 to 24.9) at common heights. For South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds, NICE puts the upper end lower, at a BMI of 22.9.
| Height | Pounds | Stone | Kilograms |
|---|---|---|---|
| 4′10″ (147 cm) | 89–119 lb | 6 st 5 lb – 8 st 7 lb | 40.2–54.0 kg |
| 5′0″ (152 cm) | 95–127 lb | 6 st 11 lb – 9 st 1 lb | 43.0–57.8 kg |
| 5′2″ (157 cm) | 101–136 lb | 7 st 3 lb – 9 st 10 lb | 45.9–61.8 kg |
| 5′4″ (163 cm) | 108–145 lb | 7 st 10 lb – 10 st 5 lb | 48.9–65.8 kg |
| 5′6″ (168 cm) | 115–154 lb | 8 st 3 lb – 11 st 0 lb | 52.0–70.0 kg |
| 5′8″ (173 cm) | 122–164 lb | 8 st 10 lb – 11 st 10 lb | 55.2–74.3 kg |
| 5′10″ (178 cm) | 129–174 lb | 9 st 3 lb – 12 st 6 lb | 58.5–78.7 kg |
| 6′0″ (183 cm) | 136–184 lb | 9 st 10 lb – 13 st 2 lb | 61.9–83.3 kg |
| 6′2″ (188 cm) | 144–194 lb | 10 st 4 lb – 13 st 12 lb | 65.4–88.0 kg |
| 6′4″ (193 cm) | 152–205 lb | 10 st 12 lb – 14 st 9 lb | 68.9–92.8 kg |
How BMI is calculated
In metric units, BMI = weight (kg) ÷ height (m)². For example, 70 kg at 1.75 m is 70 ÷ (1.75 × 1.75) = 22.9. In US units, BMI = 703 × weight (lb) ÷ height (in)². In stone and pounds, convert to pounds first (1 stone = 14 lb), or let the calculator above do it.
BMI for Asian, Black and Middle Eastern adults
NICE advises using lower BMI thresholds for people with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, because they tend to store more fat around the middle and their risk of type 2 diabetes and heart disease rises at a lower BMI: overweight from 23 and obesity from 27.5. Tick the box above to apply them.
What BMI can't tell you
- Muscle. NICE advises interpreting BMI with caution in people with high muscle mass, because muscle weighs more than fat.
- Where you carry weight. Fat around the waist carries more risk. NICE recommends also checking your waist-to-height ratio if your BMI is under 35.
- Pregnancy and under-18s. This calculator isn't for pregnancy, and children and teenagers need age-specific percentiles.
What to do next
- United Kingdom: adults aged 40 to 74 in England are offered a free NHS Health Check every five years; your GP can refer you to weight management support at any age.
- United States: most plans must cover obesity screening and counselling at no cost as preventive care.
- Canada: a family doctor, nurse practitioner or walk-in clinic can assess you; several provinces offer free dietitian advice through 811.
If your BMI is 27 or more with a condition such as high blood pressure, or 30 or more, weight-loss medicines may be an option — see who qualifies.
Common questions
What is a healthy BMI for a woman?
For adult women, as for men, a healthy BMI is 18.5 to 24.9. NICE uses 18.5 to 22.9 for women and men from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds. BMI isn't used to judge weight in pregnancy; your midwife or doctor uses other measures instead.
Is BMI calculated differently for men and women?
No. BMI uses the same formula, weight in kilograms divided by height in metres squared, and the same adult categories for men and women. The CDC says adult categories apply regardless of age, sex or race. What differs is how a clinician interprets it alongside your waist, health and background.
Does BMI change with age?
For adults the categories don't change with age, so a BMI of 27 counts as overweight at 30 or at 70. NICE advises interpreting BMI with caution from age 65, because a slightly higher BMI may be protective in older people. Children and teenagers use age- and sex-specific percentiles instead.
How do I work out my BMI in stone and pounds?
Choose the stone and feet option above and enter your height in feet and inches and your weight in stone and pounds; the calculator converts them for you. By hand, convert your weight to kilograms and height to metres, then divide the weight by the height squared.
Is a BMI calculator accurate?
The maths is exact, but BMI itself is a rough screening measure. It can't tell muscle from fat or show where you carry weight, so NICE advises caution for very muscular people and adults over 65, and recommends adding a waist-to-height ratio. Treat it as a starting point for a conversation, not a verdict.
Sources
- CDC. Adult BMI categories.
- CDC. Child and Teen BMI Calculator (ages 2 to 19).
- NICE. Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity. 2025.
- NHS. BMI calculator for adults.
- NHS. NHS Health Check.
- HealthCare.gov. Preventive care benefits for adults — obesity screening and counselling.
General information, not medical advice — see our medical disclaimer. These results are estimates and can't diagnose anything. In an emergency, call 911 (US, Canada) or 999 (UK).