Free BMI Calculator

BMI Calculator

Enter your height and weight to calculate your Body Mass Index. See which category you fall into and what the healthy weight range looks like for your height.

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Background

A BMI calculator takes your height and weight and produces a single number — your Body Mass Index. This number gives a rough estimate of whether your weight is in a healthy range for your height. Doctors, fitness professionals, and insurance companies use BMI as a quick screening tool.

This free online BMI calculator supports both imperial (feet/inches, pounds) and metric (centimeters, kilograms) units. It shows your BMI value, category, and the healthy weight range for your height.

Enter your measurements

Pick your unit system (imperial or metric), then type your height and weight. The calculator updates your BMI, category, and healthy weight range as you type.

Height5'10"
Weight170 lbs
BMI24.4

How to use this BMI calculator

Two inputs, instant result:

1

Choose your units

Tap Imperial for feet/inches and pounds. Tap Metric for centimeters and kilograms.

2

Enter height & weight

Type your height and weight. The BMI value, category, and healthy range update immediately.

3

Read your result

Your BMI number and category (Underweight, Normal, Overweight, or Obese) appear in the results panel.

How this BMI calculator works

BMI divides your weight by the square of your height. The result places you in one of four categories defined by the World Health Organization.

Step 1 — Convert height to meters
Height in inches × 0.0254 = meters
70 in × 0.0254 = 1.778 m
Step 2 — Convert weight to kg
Weight in lbs × 0.4536 = kg
170 lbs × 0.4536 = 77.1 kg
Step 3 — Calculate BMI
BMI = kg ÷ m²
77.1 ÷ (1.778)² = 24.4

Formula & Equation Used

Two versions of the BMI formula — one for metric, one for imperial:

BMI=weight (kg)÷height (m)²
BMI=weight (lbs)× 703÷height (in)²

Try it yourself

BMI24.5
CategoryNormal weight

Example Problem & Step-by-Step Solution

A person is 5 feet 8 inches tall and weighs 185 pounds. What is their BMI and category?

Step 1 — Convert height to inches
5 feet × 12 = 60 inches + 8 = 68 inches
Total height = 68 inches
Step 2 — Apply the imperial BMI formula
(185 × 703) ÷ (68 × 68) = 130,055 ÷ 4,624
BMI = 28.1
Step 3 — Determine the category
25.0 – 29.9 = Overweight
Category: Overweight. Healthy weight for 5'8" is 125-163 lbs (BMI 18.5-24.9).

Frequently Asked Questions

Is BMI accurate for muscular people?

No. BMI doesn't distinguish between muscle and fat. Athletes and bodybuilders often have a "overweight" or "obese" BMI despite having low body fat. For these individuals, body fat percentage is a better measure.

What BMI is considered healthy?

A BMI between 18.5 and 24.9 is classified as "normal weight" by the WHO. Below 18.5 is underweight, 25-29.9 is overweight, and 30+ is obese. These ranges are guidelines — individual health depends on many factors beyond BMI.

Does BMI change with age?

BMI categories are the same for adults 20+. For children and teens, BMI is plotted on age-specific growth charts using percentiles. Some researchers argue that slightly higher BMIs (25-27) may be protective for older adults.

What are better alternatives to BMI?

Waist circumference, waist-to-hip ratio, body fat percentage (via DEXA scan or calipers), and the Body Roundness Index are all more nuanced measures. BMI is a screening tool, not a diagnostic one.

What is BMI?

Body Mass Index (BMI) is a numerical value derived from a person's weight and height. Belgian mathematician Adolphe Quetelet created it in the 1830s as a tool for population-level statistics — not individual health assessment. It became widely used in medicine because it's simple and cheap to calculate.

BMI has real limitations. It can't tell the difference between muscle, bone, and fat. A person at BMI 26 could be a muscular athlete or a sedentary office worker — the number alone doesn't say which. But for large populations, BMI correlates well with health risks like heart disease and diabetes.

BMI category history

1830s
Adolphe Quetelet develops the "Quetelet Index" — weight divided by height squared — to study population patterns, not individual fitness.
1972
Researcher Ancel Keys renames it "Body Mass Index" and publishes data showing it correlates with body fat in large studies.
1985
NIH begins using BMI to define obesity. The thresholds are initially set higher than today's values.
1998
NIH lowers the "overweight" cutoff from 27.8 to 25. Overnight, millions of Americans are reclassified from normal to overweight.
Today
BMI remains the most commonly used screening tool worldwide, despite growing criticism about its limitations for individuals. Better alternatives exist but are harder to measure.

BMI categories at a glance

The World Health Organization defines four adult BMI categories:

Under<18.5
Normal18.5-24.9
Over25-29.9
Obese30+
BMI 18.5-24.9. Associated with the lowest health risks. Most guidelines target this range.

Healthy weight ranges by height

5'0" (152 cm)
97-128 lbs
5'4" (163 cm)
110-145 lbs
5'8" (173 cm)
125-163 lbs
5'10" (178 cm)
132-174 lbs
6'0" (183 cm)
140-184 lbs
6'2" (188 cm)
148-194 lbs
6'4" (193 cm)
156-204 lbs

BMI by the numbers

41.9%
of US adults classified as obese (BMI 30+)
73.6%
of US adults are overweight or obese
25.8
average BMI of American adults
1 in 5
US children aged 2-19 have obesity
$173B
annual US medical cost of obesity
1830
year BMI was first developed by Quetelet

BMI standards around the world

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WHO standard

•Underweight: <18.5
•Normal: 18.5-24.9
•Overweight: 25-29.9, Obese: 30+
The WHO categories are used worldwide as the default standard. They were developed primarily from studies on European populations. Critics argue they may not apply equally to all ethnic groups, as body composition varies between populations.
🌏

Asian standard

•Overweight starts at BMI 23 (not 25)
•Obese starts at BMI 27.5 (not 30)
•Used in Japan, China, India, and Southeast Asia
Asian populations tend to have higher body fat percentages at the same BMI compared to Europeans. This means health risks begin at lower BMI values. The WHO recognized this in 2004 by recommending lower cutoff points for Asian populations.
👶

Children & teens

•BMI plotted on age-specific growth charts
•Uses percentiles instead of fixed numbers
•85th-95th percentile = overweight, 95th+ = obese
Children's BMI changes as they grow. A healthy BMI for a 5-year-old is different from a 15-year-old. The CDC provides age and sex-specific growth charts. A child at the 85th percentile has a higher BMI than 85% of children their age and sex.

Calculator features explained

📏

Unit toggle

Switch between Imperial (feet/inches, pounds) and Metric (centimeters, kilograms). The calculator converts automatically.

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BMI result

Your BMI value and category update instantly as you type. The healthy weight range shows what you'd weigh at BMI 18.5-24.9.

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Copy results

Hit Copy to send your BMI, category, and healthy range to the clipboard for sharing with a doctor or fitness tracker.

FAQ

How do I calculate BMI manually?

In metric: divide your weight in kg by your height in meters squared. 75 kg ÷ (1.75 m × 1.75 m) = 24.5. In imperial: multiply weight in pounds by 703, then divide by height in inches squared.

Is BMI the same for men and women?

The BMI formula and categories are the same. But women naturally carry more body fat than men at the same BMI. A woman at BMI 24 and a man at BMI 24 have different body compositions. That's one of BMI's limitations.

Can BMI be too low?

Yes. A BMI below 18.5 is classified as underweight and carries health risks including weakened immune system, bone loss, and nutritional deficiencies. If your BMI is below 18.5, consult a healthcare provider.