BMI uses the same formula for adult men and women: weight in kilograms divided by height in metres squared, with no separate multiplier for sex. A 68 kg woman who is 1.65 m tall has a BMI of 25.0 kg/m², calculated exactly as it would be for a man of the same weight and height.
Is the BMI formula different for women?
Square 1.65 m: 1.65 × 1.65 = 2.7225 m². Divide 68 by 2.7225: 68 ÷ 2.7225 = 24.98, displayed as 25.0. Under the standard adult brackets — underweight below 18.5, healthy weight 18.5 to 24.9, overweight 25 to 29.9, obesity 30 and above — this value sits right at the healthy-to-overweight boundary. A man of the identical 68 kg and 1.65 m receives the identical 25.0 result from the identical formula.
How do I calculate BMI the same way for anyone?
Enter weight in kilograms and height in metres into the BMI calculator; the arithmetic does not branch on a sex input for adults. If weight or height is recorded in pounds, stones, or inches, convert with the weight converter before dividing, since the formula requires metric units unless a separate imperial constant is used instead.
What should I check about the classification used?
Confirm the classification for adults 20 and older uses the fixed brackets above, not an age- or sex-specific percentile; percentile classification applies to children and teens instead, covered in a separate guide. Check that the same person’s BMI stays constant regardless of which calculator on the site computed it, since only one formula exists for adults.
What does BMI not reveal about sex differences?
Do not expect the calculator to ask for sex and then apply a different multiplier; for adults it does not. Do not treat BMI as a body-fat percentage: CDC notes that women have more total body fat than men at the same BMI value, which the BMI number itself does not reveal. Do not apply the adult brackets to anyone under 20; that comparison is covered in the child-and-teen BMI guide.
When does the standard adult BMI calculation not apply?
BMI is a screening measure of weight relative to height. It does not measure body-fat distribution, does not diagnose a health condition, and its adult categories are not intended for pregnancy, certain medical conditions, or people with unusually high muscle mass, where a clinician’s interpretation matters more than the raw number.
Source for the external fact
CDC states that adult BMI is calculated the same way for men and women, and separately notes that women tend to have more body fat than men at an equivalent BMI, in its About Body Mass Index page.
A worked example in pounds and inches
The same calculation works in U.S. customary units with a different constant. CDC states the imperial formula as BMI = weight (lb) ÷ height (in)² × 703. For someone 5 ft 9 in (69 in) tall weighing 160 lb: 703 × 160 ÷ (69 × 69) = 112,480 ÷ 4,761 = 23.63, rounded to 23.6. Converting the same person to metric first — 160 lb is 72.57 kg, 69 in is 1.7526 m — gives 72.57 ÷ 1.7526² = 23.63, the identical result either way. The 703 constant only rescales pounds and inches into the same kilograms-per-metre-squared answer; it does not introduce a sex term.
How adult obesity is further divided into classes
Beyond the four broad brackets, CDC subdivides the obesity category itself, again with a single scale for men and women.
| Category | BMI range (kg/m²) |
|---|---|
| Class 1 obesity | 30 to under 35 |
| Class 2 obesity | 35 to under 40 |
| Class 3 obesity | 40 or higher |
CDC lists these obesity classes on its adult BMI categories page.
How to find the healthy-weight range for a given height
The formula can be solved backward to find a weight range instead of a single BMI value. For the 1.65 m height used in the worked example, the healthy-weight bracket (BMI 18.5 to under 25) runs from 18.5 × 1.65² = 50.4 kg up to just under 25 × 1.65² = 68.1 kg. The example person’s 68 kg sits just inside that upper edge — which is why the calculated 25.0 result reads as a boundary case rather than a clearly overweight one.
What to do when a result lands exactly on a bracket edge
The 68 kg, 1.65 m example computes to a precise BMI of 24.977, not exactly 25.0. Rounded to one decimal place, as the calculator displays it, that becomes 25.0 — sitting visually on the healthy/overweight line. Rounded to two decimal places instead, it is 24.98, still under 25.0 and therefore still inside the healthy bracket as CDC defines it. When a displayed, rounded BMI lands exactly on a bracket boundary, checking the unrounded figure — or re-entering the same weight and height with one more decimal of precision — shows which side of the line the value actually falls on.
Working from a height given in feet and inches
A height stated as feet and inches needs converting to a single unit before either version of the formula applies. 5 ft 4 in converts to 5 × 12 + 4 = 64 total inches, or 64 × 0.0254 = 1.6256 m. For a 140 lb person at that height, the metric route gives 140 × 0.45359237 ÷ 1.6256² = 24.03, and the imperial route gives 703 × 140 ÷ 64² = 24.03 — the same figure, confirming that mixing feet-and-inches notation only requires an extra conversion step, not a different formula.
Why measuring height with shoes on matters near a boundary
A small height-measurement error changes BMI more than it might seem, because height is squared in the formula. Measuring the 68 kg, 1.65 m example person with roughly 2 cm of shoe height added, at 1.67 m, gives 68 ÷ 1.67² = 24.38 instead of 24.98 — a 0.6-point drop from a measurement difference most people would not notice. For a result that already sits close to a bracket edge, as this example does, a barefoot, standing-straight height measurement matters more than it does for a result well inside a bracket.
How many kilograms shift a BMI reading by one full point
Because the formula divides by height squared, the same weight change moves BMI by a different amount depending on height. One BMI point equals a weight change of height² kilograms.
| Height | Weight change for 1 BMI point |
|---|---|
| 1.55 m | 2.40 kg |
| 1.65 m | 2.72 kg |
| 1.75 m | 3.06 kg |
| 1.85 m | 3.42 kg |
A taller person’s BMI is less sensitive, kilogram for kilogram, to the same weight change than a shorter person’s — not because the formula treats them differently, but because the height-squared denominator is larger.
Why the adult formula does not ask for an age either
The calculator does not branch on sex for an adult, and it does not branch on age for an adult either: a 25-year-old and a 70-year-old with the same weight and height get the identical BMI figure from the identical formula. That is a different situation from a child or teenager between ages 2 and 19, where the raw arithmetic stays the same but the classification step afterward depends on age and sex through a percentile lookup, which the child-and-teen BMI guide covers separately.
Related calculators
Calculate the formula in the BMI calculator, read its screening limits in the BMI screening-limits guide, and compare a separate body estimate in the body-fat calculator.