Adult BMI Calculator

What this calculator answers

Your body mass index (BMI) from your height and weight, the adult category it falls in, and the range of weights that counts as healthy for your height. It works in pounds with feet and inches, kilograms with centimeters, or stones and pounds, and it shows the arithmetic with your numbers. BMI is a screening measure: it describes weight for height, not body fat or health.

How to use it

• Units: choose US (feet, inches, pounds), metric (centimeters, kilograms) or UK (feet, inches, stones and pounds). Under each box the calculator shows your entry in the other units, so you can check it.
• Age: in whole years. The adult categories apply from 20. From 2 to 19 you get the BMI without a category (see below). Like the CDC’s BMI calculators, this one starts at age 2.
• Height: measured standing, without shoes. Inches can be 0 or a decimal, like 5 ft 5.5 in.
• Weight: in light clothing. Pounds and kilograms can have decimals.

The calculator doesn’t ask for sex, because the adult formula and categories are the same for everyone. Results update as you type. The Try buttons load the cases below: a 15-year-old, a BMI that rounds up to 25.0, a metric entry and a UK entry in stones. The share link includes your height and weight, so it is only made after you choose Share link and read the notice.

How to calculate BMI

Divide weight in kilograms by height in meters squared:

For pounds and inches, multiply by 703.0696, the factor that converts pounds per square inch to kilograms per square meter:

• One pound is exactly 0.45359237 kg and one inch exactly 0.0254 m, so the factor is 0.45359237 ÷ 0.0254² = 703.0696.
• The CDC’s hand formula rounds it to 703. That changes a BMI by about 0.01%, which moves the first decimal only when the BMI sits almost exactly halfway between two decimals. This calculator uses the unrounded factor, so the same person gets the same BMI in any units.
• For stones, first convert to pounds: stones × 14 + pounds.

Worked example: 5 ft 5 in and 152 lb

For an adult who is 5 ft 5 in tall, weighs 152 lb and is 38:

1. Height in inches: 5 × 12 + 5 = 65 in, and 65² = 4,225.
2. BMI = 152 ÷ 4,225 × 703.0696 = 25.29 (the rounded factor 703 gives 25.29 too).
3. Shown to one decimal: 25.3, which is at least 25 and less than 30: overweight.
4. Healthy weight at 65 in: 18.5 × 4,225 ÷ 703.0696 = 111.17 lb, up to but not including 25 × 4,225 ÷ 703.0696 = 150.23 lb. Rounded inward, that is 111.2 to 150.2 lb.
5. 152 lb is 1.8 lb above the top of that range.

In metric units the same person is 165.1 cm and 68.9 kg: 68.9 ÷ 1.651² = 68.9 ÷ 2.725801 = 25.28, also shown as 25.3. In UK units, 152 lb is 10 st 12 lb.

The example shows how close a BMI just over 25 is to the healthy range: under 2 lb at this height.

What is a healthy BMI for adults?

For adults 20 and older, a BMI of 18.5 to less than 25 is in the healthy weight range. The CDC names six categories, the same for every adult whatever their age, sex or race:

WHO uses the same thresholds for overweight (25) and obesity (30). Some tables, including the CDC’s pregnancy weight-gain table, write the ranges as 18.5–24.9 and 25.0–29.9 and call the healthy range “normal weight”; the cut-offs are the same.

Rounding at the edges. The category here comes from the unrounded BMI, because the ranges are “less than 25”, not “up to 24.9”. At 5 ft 9 in and 169 lb, BMI is 24.957: it is shown as 25.0 but is below 25, so the category is healthy weight, and the result says so in a note. A calculator that classifies the rounded 25.0 would call the same person overweight.

The CDC’s own example for a 5 ft 9 in adult does that. Its table lists whole pounds and puts 125, 169, 203 and 237 lb in the band above, which is what their BMIs rounded to one decimal (18.5, 25.0, 30.0 and 35.0) give. Unrounded, those BMIs are 18.46, 24.96, 29.98 and 34.998, so this calculator places each weight one band lower and shows the rounding note. Every other weight in that table gets the same category here.

Healthy weight range for your height

Multiply 18.5 and 25 by your height squared. In metric units that gives kilograms directly; for inches, divide by 703.0696 to get pounds. The top of the range is just under the BMI-25 weight, so this calculator rounds both ends inward to 0.1 lb or 0.1 kg: every weight it shows is inside the range. At 5 ft 9 in the range is 125.3 to 169.2 lb.

The result also lists the weight range of every category at your height, and how far your weight is from the healthy range.

BMI chart for adults

Weights at common heights, rounded inward to 0.1:

For heights in between, the calculator gives the exact figures, and its BMI chart shows the BMI at heights and weights around yours.

Reading the result

• BMI is the headline, to one decimal, with the category and its range. If rounding puts the shown BMI on a category edge it hasn’t reached, a note gives the unrounded value and the category a chart of rounded values would show instead.
• Healthy weight for your height is the range above, in your units. Compared with that range says how far your weight is below or above it, or where it sits inside it. In metric units (or In US units) repeats your height and weight in the other system.
• What BMI doesn’t tell you sits under the numbers on purpose; the next sections explain it.
• The category scale and table mark your BMI among the six categories and give the weight range of each at your height, which you can download as a CSV file.
• BMI chart around your height and weight repeats the calculation in steps of 1 inch (or 2 cm) up to 3 inches (6 cm) either side of your height, and in steps of 10 lb (1 stone, or 5 kg) up to 20 lb (2 stone, or 10 kg) either side of your weight, with your cell highlighted.

To compare, press Save for comparison, change the inputs and save again: each saved scenario shows its BMI change against the first.

Is BMI different for women, men or older adults?

No. For adults 20 and older the formula and the categories are the same at every age and for women and men, so the healthy range for a height doesn’t move with age. That is why there is no separate “BMI for women” or “BMI for men” calculation. Two people with the same BMI can still carry different amounts of fat, which is one reason BMI is a starting point rather than a verdict.

Why BMI can be misleading

BMI divides weight by height squared. It never sees what the weight is made of or where it is:

• Muscle. Muscle, bone and fat all count as weight, so a very muscular person can have a BMI in the overweight or obesity range without much body fat.
• Where fat sits. Fat around the waist is linked to a higher risk of heart disease and type 2 diabetes than fat around the hips. The NHLBI names a waist over 35 inches for women or 40 inches for men as a sign of higher risk, something BMI can’t show.
• Ancestry. A WHO expert consultation found that in many Asian populations a large share of people have a high risk of type 2 diabetes and heart disease at BMIs below 25. WHO kept the international cut-offs and left countries to decide on lower action points, so this calculator uses 18.5, 25 and 30.
• Pregnancy. The categories don’t apply to weight during pregnancy (see the questions below).

A health care provider reads BMI together with other checks, such as blood pressure, cholesterol and a physical exam. This page describes BMI; it is not medical advice or a diagnosis.

BMI for children and teens

From 2 through 19, BMI is compared with children and teens of the same age and sex on growth charts, and the result is a percentile, not an adult category. Enter an age under 20 and this calculator shows the BMI with a note instead of a category: with the example’s 5 ft 5 in and 152 lb at age 15, the BMI is still 25.3, but whether that is high depends on the percentile for a 15-year-old boy or girl. The CDC’s Child and Teen BMI Calculator gives the percentile.

Common mistakes

• Typing meters in the centimeter box. 1.65 is refused because height must be at least 50 cm. Enter 165.
• Entering kilograms with US units selected. 69 “lb” at 5 ft 5 in gives a BMI under 12; the calculator warns that such a low BMI is rare and asks you to check the units.
• Measuring in shoes or heavy clothes. Shoes add height and lower the BMI: at 5 ft 5 in and 152 lb, an inch is worth about 0.8, and a pound of clothing about 0.17.
• Reading 25.0 as overweight. A BMI that rounds to 25.0 may still be below 25; the note under the headline says which side you are on.
• Using the adult categories for a teenager. A 16-year-old’s BMI needs the BMI-for-age percentile.
• Treating the healthy range as a target set in stone. It is a population screening range; your own healthy weight depends on things BMI doesn’t measure.