BMI Calculator: Calculate Your Body Mass Index

Everything on this page runs in your browser. Your height and weight are not sent to us, not saved to an account, and not emailed to anyone. There is no email gate: no step where the number is held back until you hand over an address, because that practice exists to collect addresses rather than to answer the question you came with. Close the tab and the numbers are gone.

BMI uses height and weight only. There is no age field and no sex field, because the formula does not use them.

BMI is one division and one multiplication. It scales body mass to the square of height so that people of different heights can be compared on the same axis. There are two ways to write it, and they describe the same quantity.

The 703 is not a fudge factor. BMI is defined in metric units, so the US version has to carry the conversion inside it. One pound is 0.45359237 kilograms and one inch is 0.0254 meters, so converting pounds and inches into kilograms and meters squared works out to 0.45359237 ÷ 0.0254², which is 703.06957 and change. The published formula rounds that to 703. That rounding is why a US-unit BMI and a metric BMI can differ in the second decimal place, which is also why this calculator computes from one set of units and converts for display rather than running the arithmetic twice.

This is the original definition, published in the 19th century by the Belgian mathematician Adolphe Quetelet as the Quetelet index. He was describing populations, not patients, and the measure was not built to assess an individual. The name body mass index came more than a century later.

That is the whole calculation. Notice how little went into it: two measurements, no labs, no waist, no training history, no age past the cutoff for adult categories. What comes out is a screening estimate, not a diagnosis.

The adult categories are fixed cutoffs on the BMI scale. They do not change with age after 20, and they do not change by sex.

Every cell below is the BMI for that height and weight, computed with the same formula the calculator uses. Heights run from 5 ft 0 in to 6 ft 6 in in one-inch steps. Scroll the grid sideways to see the heavier columns.

For adults 20 and older, 18.5 to 24.9 is the range international health bodies label normal weight. The World Health Organization fact sheet on obesity and overweight sets out those adult cutoffs and the reasoning behind them.

Read that range for what it is. It describes statistical associations across large populations between a height-scaled weight and health outcomes. It is not a verdict on an individual, and a BMI inside it is not a clean bill of health any more than a BMI outside it is a diagnosis. Two people at 23.0 can have completely different waist measurements, lipid panels, fasting insulin, and training histories, and those differences matter more than the shared number.

The useful question is never "is my BMI good." It is what the number, taken together with everything BMI leaves out, suggests a clinician should look at next.

BMI survives because it is cheap, fast, and reproducible. Those are real virtues for a population screen. They are also the reason it fails at the individual level: a measure that only knows your height and your weight cannot know anything else about you.

Take two people who are both 5 ft 10 in and both 200 lb. One trains four days a week and carries substantial lean mass at a low body-fat percentage. The other has not trained in a decade. Both have a BMI of 28.7, and both are classified overweight. The number is identical because the inputs are identical, and the inputs cannot see what the weight is made of.

Body composition, not total mass, is what tracks with metabolic health. Muscle is denser than fat, so adding lean mass raises BMI while typically improving the things BMI is used as a proxy for. That is a screening tool disagreeing with itself.

Visceral fat, stored around the organs in the abdomen, behaves differently from subcutaneous fat stored under the skin, and the two carry different metabolic risk. BMI cannot see the difference because location is not one of its inputs. Waist circumference and waist-to-height ratio do capture it, which is why the National Heart, Lung, and Blood Institute guidance on aiming for a healthy weight pairs a BMI reading with a waist measurement rather than using BMI on its own.

The index began as a 19th-century population statistic, a way to describe the distribution of body size across a group. It was never derived as a diagnostic instrument, and applying a group-level average to one person imports error that the original measure was never designed to control. Rothman KJ, BMI-related errors in the measurement of obesity, International Journal of Obesity, 2008 works through where that error comes from and how it behaves.

The practical consequence is modest and worth stating plainly: BMI is a flag that tells a clinician to look closer. It is not the looking closer.

None of the following replaces BMI so much as it makes BMI usable, by supplying the information a height-and-weight ratio cannot carry.

• Waist circumference. A tape measure at the level of the navel captures abdominal fat, which BMI cannot see at all.
• Waist-to-height ratio. Dividing waist by height normalizes the waist measurement across body sizes and is simple enough to repeat at home.
• Resting labs. A1c, a lipid panel, and fasting insulin describe how the body is actually handling fuel, which is the thing BMI is being used as a stand-in for.
• Strength and lean-mass trend over time. What direction your lean mass and your working strength are moving says more about the year ahead than a single ratio does.

Taken together, those shift the question from weight to body composition, which is the more honest frame. If you want the energy side of that picture, the TDEE calculator (your total daily burn) estimates how much your body uses in a day, which is a different question from what your mass divided by your height squared happens to be.

There is one formula and one set of adult cutoffs. A BMI of 27.0 is classified overweight whether the person is a man or a woman, and there is no separate chart for either. Anyone offering you a women-only or men-only BMI chart for adults is inventing a distinction the measure does not make.

What does differ is what the number hides. At the same BMI, women typically carry a higher body-fat percentage and men typically carry more lean mass, so the same value sits on a different body composition. Fat distribution patterns also differ on average. Both of those are arguments for reading BMI alongside a waist measurement and labs, and neither is an argument for a different formula.

Men use the same BMI calculator as women. A male BMI of 27.0 is classified overweight on the identical adult scale. There is no separate male BMI formula, no men’s BMI chart, and no adjustment for sex.

The one measurement that genuinely is sex-specific is waist circumference. The National Heart, Lung, and Blood Institute puts the elevated-risk threshold at more than 40 inches for men, versus more than 35 inches for women, because fat carried around the waist rather than the hips raises the risk of heart disease and type 2 diabetes. NHLBI guidance on healthy weight and waist circumference sets out both figures. For a man whose BMI reads overweight, the waist number is usually the more informative of the two.

BMI often misreads men who lift, because the formula cannot tell dense muscle from fat. A muscular man can land in the overweight or obese range at a low body-fat percentage. That is a limitation of the measure, not a finding about him.

The cutoffs do not change. For every adult 20 and older, 18.5 to 24.9 is the normal weight range regardless of age. What changes with age is the body underneath the number: lean mass declines and fat tends to increase, so a man can hold the same weight and the same BMI at 55 as at 35 while carrying meaningfully more fat and less muscle. BMI can therefore understate body fat as adults age, which is another reason to read it beside a waist measurement rather than on its own.

Protocol MD is a physician-guided peptide therapy practice. Licensed clinicians review labs, history, and goals across performance, longevity, and body composition, alongside recovery, sleep, energy, and cellular health.

If you want the background before anything else, here is what peptide therapy is and how it is used.

A calculator cannot tell you whether any treatment is appropriate for you. Only a licensed physician can, after a full assessment. If that is the conversation you want to have, you can start the physician-guided assessment.