How it’s calculated

BMI = weight (kg) ÷ height (m)² Imperial: BMI = 703 × weight (lb) ÷ height (in)²

Worked example: 200 lb at 5 ft 9 in (69 in): 703 × 200 ÷ (69 × 69) = 140,600 ÷ 4,761 = 29.5 — the overweight range.

Metric: 90 kg at 1.70 m: 1.70 × 1.70 = 2.89, and 90 ÷ 2.89 = 31.1 — obesity class I.

The calculator uses the exact metric conversion, so its imperial results can differ from the 703 shortcut in the second decimal.

Adult BMI categories

The same cut-offs are used by the World Health Organization and the CDC for adults.

Category (adults)	BMI (kg/m²)
Underweight	below 18.5
Healthy weight	18.5 – 24.9
Overweight	25.0 – 29.9
Obesity class I	30.0 – 34.9
Obesity class II	35.0 – 39.9
Obesity class III	40.0 or more

Weight range for BMI 18.5–24.9 by height

What a BMI of 18.5 and of 24.9 works out to at common heights. It’s a reference range, not a personal target.

Height	BMI 18.5	BMI 24.9
4 ft 10 in	89 lb	119 lb
5 ft 0 in	95 lb	127 lb
5 ft 2 in	101 lb	136 lb
5 ft 4 in	108 lb	145 lb
5 ft 6 in	115 lb	154 lb
5 ft 8 in	122 lb	164 lb
5 ft 10 in	129 lb	174 lb
6 ft 0 in	136 lb	184 lb
6 ft 2 in	144 lb	194 lb
6 ft 4 in	152 lb	205 lb

What BMI can’t tell you

It doesn’t measure body fat. BMI can’t tell muscle from fat or bone, so a muscular person can land in the “overweight” range with little body fat.
It doesn’t show where fat is. The WHO calls BMI a surrogate marker of fatness; measurements such as waist circumference add information.
It means different things for different people. People of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background have health risks at lower BMIs — the NHS uses 23–27.4 as overweight and 27.5 or more as obesity for them. At the same BMI, body fat also tends to differ with age and sex.
It isn’t for children, teens or pregnancy. Under-18s (under-20s in US charts) are assessed with age- and sex-specific BMI percentiles, and BMI isn’t used to judge weight during pregnancy.
It’s a screening number, not a diagnosis. A clinician looks at BMI alongside your history, measurements, blood pressure and lab results.

Frequently asked questions

What is a healthy BMI?

For most adults, 18.5 to 24.9 is described as the healthy range. It’s a population guideline: it can’t account for muscle, ethnicity or age, and your clinician will look at more than BMI.

How do I calculate BMI with pounds and inches?

Multiply your weight in pounds by 703, then divide by your height in inches squared. For 160 lb at 5 ft 5 in (65 in): 703 × 160 ÷ 4,225 = 26.6.

Is BMI accurate for muscular people?

Not very. Muscle is dense, so athletes and people who lift can have a “high” BMI with little body fat. Waist measurements or a body-composition test give a better picture.

Why are the BMI cut-offs lower for some ethnic groups?

People from some backgrounds have a higher chance of health problems at a lower BMI, so the NHS uses lower thresholds — 23 and 27.5 — for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background.

Can I use this BMI calculator for my child?

No. Children and teens need a BMI-for-age percentile, which compares them with others of the same age and sex. Ask your pediatrician or use a child-specific calculator.

Informational only, not medical advice. These calculators do simple arithmetic on the numbers you enter. They don’t diagnose anything and don’t replace your clinician or dietitian. Nothing you type is sent anywhere — it stays in your browser. Updated September 2026.

BMI calculator