BMI Calculator: Work Out Your Body Mass Index Free

How to calculate BMI

BMI is your weight in kilograms divided by your height in metres, squared. Someone 1.75 m tall who weighs 70 kg divides 70 by 3.0625 and gets 22.9.

Pounds and inches need a conversion factor of 703. The same person at 5 ft 9 in (69 inches) and 154 lb works out 703 x 154 / 4,761, which comes back to 22.7. The 0.2 gap is rounding rather than a different formula: 1.75 m is 68.9 inches, not 69, and 70 kg is 154.3 lb. The calculator above runs whichever version matches the units you picked.

Two worked examples, if you want to check the arithmetic against your own numbers:

Metric. 82 kg at 1.68 m. Square the height: 1.68 x 1.68 = 2.8224. Then 82 / 2.8224 = 29.1, which is the top of the overweight band.
Imperial. 200 lb at 5 ft 11 in, so 71 inches. Square it: 71 x 71 = 5,041. Then 703 x 200 / 5,041 = 27.9.

The order does not matter as long as you square the height before dividing. The most common mistake is using height in centimetres instead of metres, which turns that 22.9 into 0.0023 and tells you the units are wrong.

Adolphe Quetelet built the ratio in the 1830s to describe populations, not people. The name arrived in 1972, when Ancel Keys compared it against the other height-weight indices of the day and found it the least bad option for comparing groups. Nobody designed it to score an individual, which explains most of what follows.

BMI chart for adults

BMI	Category	Weight at 5 ft 9 in / 175 cm
Under 18.5	Underweight	Under 57 kg / 126 lb
18.5 to 24.9	Healthy weight	57 to 76 kg / 126 to 169 lb
25.0 to 29.9	Overweight	77 to 91 kg / 170 to 203 lb
30.0 to 34.9	Obese, class I	92 to 107 kg / 204 to 237 lb
35.0 to 39.9	Obese, class II	108 to 122 kg / 238 to 270 lb
40.0 and above	Obese, class III	123 kg / 271 lb and above

Anyone under 20 is scored differently, against growth percentiles for age and sex. Reading a 14-year-old off the adult chart will label them wrongly in either direction.

Several health services shift the thresholds for people of South Asian, Chinese, Japanese and other Asian descent, where the risk of type 2 diabetes and cardiovascular disease climbs at a lower BMI. NICE in the UK moves the overweight line to 23 and the obesity line to 27.5 for those groups.

Healthy weight by height, in pounds

The same categories read the other way round: what you weigh for your height rather than what your height and weight score.

Height	Healthy (BMI 18.5–24.9)	Overweight (25–29.9)	Obesity (30+)
5 ft 0 in	95–128 lb	129–153 lb	154 lb and up
5 ft 1 in	98–132 lb	133–158 lb	159 lb and up
5 ft 2 in	102–136 lb	137–164 lb	165 lb and up
5 ft 3 in	105–141 lb	142–169 lb	170 lb and up
5 ft 4 in	108–145 lb	146–174 lb	175 lb and up
5 ft 5 in	112–150 lb	151–180 lb	181 lb and up
5 ft 6 in	115–154 lb	155–185 lb	186 lb and up
5 ft 7 in	119–159 lb	160–191 lb	192 lb and up
5 ft 8 in	122–164 lb	165–197 lb	198 lb and up
5 ft 9 in	126–169 lb	170–203 lb	204 lb and up
5 ft 10 in	129–174 lb	175–209 lb	210 lb and up
5 ft 11 in	133–179 lb	180–215 lb	216 lb and up
6 ft 0 in	137–184 lb	185–221 lb	222 lb and up
6 ft 1 in	141–189 lb	190–227 lb	228 lb and up
6 ft 2 in	145–194 lb	195–233 lb	234 lb and up
6 ft 3 in	149–200 lb	201–240 lb	241 lb and up
6 ft 4 in	152–205 lb	206–246 lb	247 lb and up

The healthy band is wider than most people expect. At 5 ft 5 in it runs from 112 to 150 lb, a spread of 38 lb, and every weight inside it scores as healthy. Picking a single number out of that range is a decision about how you want to look and train, not a medical instruction.

Healthy weight by height, in kilograms

Height	Healthy (BMI 18.5–24.9)	Overweight (25–29.9)	Obesity (30+)
150 cm	42–56 kg	57–67 kg	68 kg and up
155 cm	45–60 kg	61–72 kg	73 kg and up
160 cm	48–63 kg	64–76 kg	77 kg and up
165 cm	51–68 kg	69–81 kg	82 kg and up
170 cm	54–72 kg	73–86 kg	87 kg and up
175 cm	57–76 kg	77–91 kg	92 kg and up
180 cm	60–80 kg	81–97 kg	98 kg and up
185 cm	64–85 kg	86–102 kg	103 kg and up
190 cm	67–90 kg	91–108 kg	109 kg and up
195 cm	71–95 kg	96–114 kg	115 kg and up

BMI charts for men and women

Men and women read the same chart. There is no separate BMI chart for men, and any site offering one is splitting a number that was never split. The formula has no term for sex, and neither do the thresholds.

What differs is body composition, not the cut-off. A woman and a man at BMI 24 carry roughly 10 percentage points of body fat between them, because women hold more essential fat around the breasts, hips and thighs. That is a good argument for measuring composition directly rather than for redrawing the table. The body fat calculator uses tape measurements and does apply different formulas to men and women, which is where the distinction genuinely belongs.

One practical consequence: a woman at BMI 22 and a man at BMI 22 are not in the same physical state, and comparing your number against a partner’s tells you very little.

What each BMI number means

The bands are administrative lines drawn across a continuous risk curve. Nothing changes about your body at 24.9 that changes again at 25.0.

Under 18.5. Underweight. Associated with lower bone density, reduced immune function and, in large population studies, a mortality risk comparable to the overweight band. This end of the chart gets far less attention than it deserves.
18.5 to 24.9. Healthy weight. A 38 lb range at 5 ft 5 in and 43 lb at 5 ft 9 in, not a target.
25 to 29.9. Overweight. Risk of type 2 diabetes and cardiovascular disease starts rising, though this is also the band where muscular people are misclassified most often.
30 to 34.9. Obesity class I.
35 to 39.9. Obesity class II.
40 and above. Obesity class III, sometimes called severe or morbid obesity. This is the threshold most bariatric surgery criteria use, or 35 with a related condition such as type 2 diabetes.

Waist measurement adds information the bands cannot. Keeping your waist under half your height is the simplest version of that check, and it separates two people at the same BMI better than the BMI does.

What your BMI actually tells you

It tells you how heavy you are for your height, and that is the whole of it. Across a population that correlates well with body fat, which is why epidemiologists still use it. Across one person it can be wildly off, because the formula counts a kilogram of muscle and a kilogram of fat identically. What BMI measures, and what it misses works through where the correlation holds and where it breaks.

A reading of 27 on a 95 kg rugby forward and a reading of 27 on a 95 kg office worker describe two different bodies with two different risk profiles. The number cannot separate them. A tape measure can, and the Navy method guide covers how to take those measurements without fooling yourself.

BMI is also blind to fat distribution. Visceral fat around the organs carries more metabolic risk than the same mass on the hips and thighs, and two people at BMI 28 can differ sharply on that.

Reaching a healthy BMI

The calculator returns a weight range rather than a target, because the healthy band spans about 20 kg at average height. Landing anywhere inside it is the goal. The ideal weight calculator shows what the older clinical formulas suggest for the same height, and they usually sit near the middle of that band.

Getting there is an energy question. Work out what you burn with the calorie and TDEE calculator, then read how big a calorie deficit should be before you pick a number to eat.

One warning about tracking progress: your weight moves 1 to 2 kg within a single day on glycogen, sodium and gut contents alone, which shows up as a BMI swing of half a point. Weigh at the same time under the same conditions and compare weekly averages. Why the scale jumps overnight covers what is really moving.

Common questions

What is a healthy BMI?

For adults, 18.5 to 24.9 is the healthy range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese. The same cut-offs apply to men and women. Children and teenagers are scored against age and sex percentiles instead, so an adult BMI reading does not apply to them.

How do I calculate BMI by hand?

In metric, divide your weight in kilograms by your height in metres squared. Someone 1.75 m and 70 kg works out at 70 / (1.75 x 1.75) = 22.9. In imperial, multiply your weight in pounds by 703, then divide twice by your height in inches.

Is BMI accurate for athletes?

No. BMI counts every kilogram the same way, and muscle is denser than fat, so a lean rugby forward or powerlifter routinely scores 28 or higher while carrying single-digit body fat. If you train heavily, a tape measurement is the better read.

Does BMI use different numbers for men and women?

The formula and the thresholds are identical. Women carry more essential fat at any given BMI, roughly 10 percentage points more on average, which is one reason the number tells you about weight-for-height rather than about body composition.

What BMI is considered obese?

30 and above. Clinicians often split that further: 30 to 34.9 as class I, 35 to 39.9 as class II, and 40 or more as class III. Some health services apply lower thresholds for people of South Asian, Chinese and other Asian descent, where metabolic risk climbs at a lower BMI.

What is a healthy weight for my height?

At 5 ft 5 in the healthy range is 112 to 150 lb, at 5 ft 9 in it is 126 to 169 lb, and at 6 ft 0 in it is 137 to 184 lb. The same ranges apply to men and women. Every weight inside the band scores as healthy, so the range is the answer rather than a single number within it.

What does a BMI of 25 mean?

It is the first point of the overweight band, which runs from 25 up to 30. Nothing changes about your body between 24.9 and 25.0; the line is an administrative cut across a continuous risk curve. At 25 exactly, waist measurement and body composition tell you far more than the BMI does.

BMI Calculator