BMI Calculator

Enter your height and weight to get your BMI, the category it falls in, and the weight range that would put you in the healthy band for your height.

How BMI works

Body mass index is a single number that relates your weight to your height. It was created in the 1830s by the Belgian statistician Adolphe Quetelet to describe the average build of a population, not to assess individuals. It survives today as a screening tool because it needs only two measurements anyone can take at home, and because at the population level it tracks body fatness closely enough to be useful.

The formula is weight (kg) ÷ height (m)², or 703 × weight (lb) ÷ height (in)² in imperial units. The result is placed in one of these bands:

Under 18.5 — underweight
18.5 – 24.9 — healthy weight
25.0 – 29.9 — overweight
30.0 – 34.9 — obesity, class 1
35.0 – 39.9 — obesity, class 2
40.0 and above — obesity, class 3

Worked example

Someone 5 ft 8 in (1.727 m) tall weighing 160 lb (72.6 kg): BMI = 72.6 ÷ 1.727² = 72.6 ÷ 2.983 =24.3 — near the top of the healthy range. To reach a BMI of 22 they would weigh about 145 lb; to cross into "overweight" at 25 they would weigh about 164 lb.

Healthy weight by height

The weight range that gives a BMI of 18.5–24.9 at common heights:

Height	Healthy weight range
5 ft 0 in	95–127 lb (43–58 kg)
5 ft 2 in	101–136 lb (46–62 kg)
5 ft 4 in	108–145 lb (49–66 kg)
5 ft 6 in	115–154 lb (52–70 kg)
5 ft 8 in	122–164 lb (55–74 kg)
5 ft 10 in	129–174 lb (58–79 kg)
6 ft 0 in	136–184 lb (62–83 kg)
6 ft 2 in	144–194 lb (65–88 kg)

Where BMI falls short

BMI measures mass, not composition, and cannot tell muscle from fat or where fat sits. A lean, heavily trained athlete can land in the "overweight" band while an inactive person with the same BMI carries far more fat (sometimes called "normal-weight obesity"). It is also a poor fit for children and teens (who need age- and sex-specific percentile charts), for pregnant people, and for the very elderly. Two better quick checks alongside it:

Waist-to-height ratio — keep your waist under half your height. This captures abdominal fat, which carries more metabolic risk and which BMI ignores completely.
Body fat percentage — estimate it from tape measurements with the body fat calculator, or from a DEXA scan for a precise figure.

If your BMI is outside the healthy range

A BMI in the overweight or obese bands is a prompt to look closer, not a verdict. If you also carry a lot of muscle, check your body fat before acting. If the number reflects excess fat and you want to change it, weight only moves through energy balance: set a modest calorie target with the calorie calculator, keep protein high using the macro calculator, and add resistance training so the weight you lose is mostly fat. A change of one BMI point is roughly 6–7 lb for an average-height adult.

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Frequently asked questions

What is a healthy BMI?

A BMI between 18.5 and 24.9 is the healthy range for most adults. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese (with obesity sometimes split into class 1 at 30–34.9, class 2 at 35–39.9, and class 3 at 40+).

How is BMI calculated?

BMI is your weight in kilograms divided by the square of your height in metres. In imperial units it is weight in pounds times 703, divided by height in inches squared. This calculator does both automatically.

What does my BMI number actually mean?

It places you on a population curve. A BMI of 24 means your weight-for-height is near the top of the range associated with the lowest average health risk in large studies. It does not measure your fitness, body fat, or health directly — two people with the same BMI can be very different.

Is BMI accurate for everyone?

No. BMI does not distinguish muscle from fat, so it overestimates body fatness in very muscular people and can underestimate it in older adults who have lost muscle. It was not designed for children, pregnant people, or competitive athletes, and some health bodies use a lower overweight threshold (23) for people of South and East Asian descent because cardiometabolic risk rises earlier.

What is a good BMI for my age?

For adults the healthy range (18.5–24.9) does not change with age. However, a slightly higher BMI (into the mid-20s) is associated with no extra risk, and sometimes lower risk, in people over about 65 — losing weight is not automatically beneficial late in life. For anyone under 20, use age- and sex-specific BMI-for-age percentiles instead.

How do I lower my BMI?

BMI only moves when body weight changes relative to height (which is fixed for adults). A sustained calorie deficit of about 500 a day trends to roughly 0.5 kg / 1 lb of weight loss per week. Use the calorie calculator to set a target and the macro calculator to keep protein high so the loss is mostly fat.

BMI vs body fat percentage — which should I use?

BMI is a free 10-second screen. Body fat percentage tells you what your weight is actually made of and is worth measuring if BMI puts you near a boundary or if you carry a lot of muscle. Waist-to-height ratio (keep your waist under half your height) is another quick check that captures abdominal fat, which BMI misses entirely.

Is BMI used to diagnose obesity?

It is used to screen for it, not diagnose it. A clinician confirming obesity will also look at waist circumference, blood pressure, blood glucose and lipids, family history, and how weight affects your daily life. BMI on its own is a starting point for that conversation.

Last reviewed: September 2026. Figures and formulas are checked against their published sources; see the site's data notes.