BMI Calculator

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Part of:The Complete BMI Guide 2026: Formula, Charts, Healthy Ranges & Alternatives

Professional review pending. BMI Calculator has passed formula and automated QA checks, but no independently verified clinician is currently attributed. Content updated September 9, 2026. Review process

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BMI Calculator

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Calculate adult BMI using kilograms and centimetres or pounds, feet, and inches. See your category and understand the result’s limitations.

Enter values above to see results.

This calculator also shows the new BMI — the Trefethen (2013) formula, 1.3 × weight (kg) ÷ height (m)^2.5 — side by side with the classic result. Proposed by Oxford mathematician Nick Trefethen to correct the height bias of the standard formula, it changes how results vary for people taller than 5'9" or shorter than 5'3". See the full explainer.

📊 BMI Chart

This BMI chart shows the standard adult weight categories and their BMI ranges. Calculate your BMI above to see your own result highlighted against the same chart.

BMI Chart — Adult Categories

Standard adult BMI category chart with weight ranges
Category	BMI range
Underweight	Below 18.5
Normal weight	18.5 – 24.9
Overweight	25.0 – 29.9
Obesity Class I	30.0 – 34.9
Obesity Class II	35.0 – 39.9
Obesity Class III	40.0 and above

Adult BMI screening categories (age 20+), WHO reference ranges. A screening category is not a diagnosis — see the FAQ below for limitations.

📜 History of BMI

1832Quetelet Index Created

Belgian mathematician Adolphe Quetelet develops the weight-to-height ratio as part of his study of human physical characteristics and social statistics. Called the "Quetelet Index," Quetelet never designed it as a health measure.

1972Ancel Keys Renames It "BMI"

American physiologist Ancel Keys publishes a landmark paper in the Journal of Chronic Diseases analyzing seven countries. He renames Quetelet's index "Body Mass Index" and promotes it as the best available proxy for body fat in population studies.

1985NIH Adopts BMI

The U.S. National Institutes of Health adopts BMI as a standard measure for adiposity research and clinical assessment.

1995WHO Global Standards

The World Health Organization establishes international obesity classification standards using BMI cutoffs: 25 for overweight and 30 for obesity.

2013AMA Recognition

The American Medical Association formally designates obesity (BMI ≥ 30) as a disease, elevating the importance of BMI screening in clinical practice.

2023Limitations Acknowledged

Major medical organizations including the AMA begin recommending BMI as one tool among many, acknowledging its limitations regarding body composition, ethnicity, and muscle mass.

📝 Worked Examples

Normal Weight

Weight:68 kg

Height:1.72 m

Calculation:68 ÷ 2.96

BMI:23.0

✓ Normal Weight

Overweight

Weight:90 kg

Height:1.75 m

Calculation:90 ÷ 3.06

BMI:29.4

⚠ Overweight

Obese Class I

Weight:100 kg

Height:1.70 m

Calculation:100 ÷ 2.89

BMI:34.6

⚠ Obese Class I

✅ Published Calculation and QA Details

Formula version BMI-2026.1 · Last QA 2026-07-30

Category thresholds use the unrounded result. The displayed BMI is rounded only for presentation, so a result of 24.96 shows as 25.0 but is still correctly categorized as Normal weight (below the 25.0 cutoff).

Published BMI calculator regression test cases
Case	Inputs	BMI	Category
Metric reference	175 cm, 70 kg	22.9	Normal weight
Metric upper-normal example	180 cm, 75 kg	23.1	Normal weight
US-unit conversion	5 ft 10 in, 180 lb	25.8	Overweight

⚠️ Limitations of BMI

BMI alone cannot determine individual health risk, treatment, or urgency. If you have concerns about your result, consider discussing it in context with a qualified clinician.

❌ Cannot distinguish fat from muscle

Athletes with high muscle mass may score a high BMI yet carry minimal body fat, producing a false obesity reading.

❌ Does not measure body fat distribution

Abdominal obesity (apple shape) carries higher risk than peripheral fat. BMI gives no information about where fat is stored.

❌ Age-related inaccuracy

Older adults tend to lose muscle mass and gain fat with age. The same BMI may represent more body fat in elderly populations.

❌ Ignores bone density

People with higher bone density may have higher BMI without excess fat, and those with osteoporosis may have lower BMI.

❌ Pregnancy limitations

BMI does not reliably indicate health status during pregnancy, as body composition and fluid distribution change substantially.

❌ Does not reflect metabolic health

“Metabolically healthy obese” individuals exist, while normal-weight individuals can have metabolic disorders.

🩺 Health Risks Linked to BMI Categories

Population studies associate higher and lower BMI categories with different average health risks. These are population-level associations, not individual predictions—an individual's actual risk depends on genetics, body composition, activity level, diet, and other factors this calculator does not measure.

Associated with higher BMI (overweight/obesity)

Cardiovascular disease, including high blood pressure and stroke
Type 2 diabetes and insulin resistance
Certain cancers (e.g., breast, colon, endometrial)
Osteoarthritis and other musculoskeletal strain
Obstructive sleep apnea and breathing difficulties
Gallbladder disease and fatty liver

Associated with lower BMI (underweight)

Nutritional deficiencies and anemia
Reduced bone density and osteoporosis risk
Weakened immune response
Fertility and reproductive complications
Growth and developmental concerns in children and teens
Higher risk of surgical and treatment complications

Sources: CDC, “BMI Frequently Asked Questions” · WHO, “Obesity and overweight” fact sheet. This is general health information, not individual medical advice.

🧒 BMI Calculator for Kids and Teens

This calculator is built for adults aged 20 and over and should not be used to assess a child's or teenager's weight. Children and teens are still growing, so a fixed adult BMI category (Underweight / Normal / Overweight / Obese) does not apply to them.

Why kids need a different method

For people ages 2–19, the CDC and WHO use BMI-for-age percentiles, which compare a child's BMI to other children of the same age and sex using growth charts — not the fixed numeric cutoffs (18.5, 25, 30) this adult calculator uses. A 10-year-old and a 16-year-old with the identical BMI number can fall into completely different percentile categories, so an adult-style BMI number for a child is not meaningful on its own.

To assess a child or teen's weight correctly, use the CDC's official BMI-for-age growth charts or ask a pediatrician — they can plot BMI-for-age percentile accurately and account for growth stage, which this general adult calculator cannot do.

📊 Obesity & Overweight Prevalence: Current Data

40.3%

of U.S. adults had obesity, Aug 2021–Aug 2023 (39.2% of men, 41.3% of women)

9.4%

of U.S. adults had severe obesity (BMI ≥ 40) in the same period

2.5B

adults worldwide were overweight in 2022 (43% of all adults)

890M

adults worldwide were living with obesity in 2022 (16% of all adults)

Sources: CDC NCHS Data Brief No. 508 (September 2024) · WHO Obesity and Overweight Fact Sheet (2022 data).

⚖️ BMI vs. Body Fat vs. Ideal Weight

Metric	BMI	Body Fat %	Ideal Weight
Measures	Weight/height ratio	Actual fat tissue %	Target weight range
Accuracy	Low for individuals	High (DEXA, Navy)	Moderate
Equipment	Scale + tape measure	Calipers or DEXA	Scale + tape measure
Cost	Free	$0–$500	Free
Best for	Population screening	Body composition	Weight goal setting
Limitations	Ignores composition	Method variability	Formula variability

Try Body Fat Calculator →Try Ideal Weight Calculator →

🌏 Ethnicity & BMI Adjustments

Some clinical guidelines use additional action points for Asian populations because population-level associations can differ at the same BMI. These are context-dependent screening thresholds, not diagnoses, and this calculator's main result uses the standard adult categories.

Standard WHO Cutoffs (General)

Underweight< 18.5

Normal18.5–24.9

Overweight25.0–29.9

Obese≥ 30.0

Additional Asian Population Action Points

Underweight< 18.5

Normal18.5–22.9

Overweight (at risk)23.0–27.5

Obese≥ 27.5

Source: WHO Expert Consultation (2004). “Appropriate body-mass index for Asian populations.” The Lancet, 363(9403), 157–163.

🩺 Discussing Your BMI Result

Underweight (BMI < 18.5)

A low BMI does not identify a cause. If the result is unexpected or you have concerns about nutrition, symptoms, or unintentional weight change, consider discussing them with a qualified clinician or registered dietitian.

Normal Weight (18.5–24.9)

Being in the reference range does not confirm that an individual is healthy. Consider BMI alongside symptoms, medical history, waist circumference, body composition, movement, nutrition, sleep, and other measures relevant to you.

Overweight (25–29.9)

This category is a screening result, not a diagnosis or instruction to lose weight. If you want help interpreting it, discuss your health history, symptoms, body composition, and goals with a qualified clinician or registered dietitian.

Obese (BMI ≥ 30)

BMI alone cannot determine treatment or urgency. Consider discussing the result and other factors—such as symptoms, medical history, waist circumference, blood pressure, and laboratory results—with a qualified clinician.

🔬 Key Research on BMI

WHO Fact Sheet

Obesity and Overweight

Current WHO statistics on global obesity prevalence and BMI classification guidance.

who.int ↗

CDC Guidelines

About Adult BMI

CDC guidance on interpreting BMI for adults with health risk information and next steps.

cdc.gov ↗

NEJM Study

BMI and Mortality Risk

Berrington de Gonzalez et al. (2010). BMI and mortality in 1.46 million white adults.

nejm.org ↗

🔍 BMI Myths vs. Facts

✕ Myth

BMI directly measures body fat

✓ Fact

BMI is a weight-for-height calculation. It does not directly measure adipose tissue or distinguish fat mass from lean mass.

✕ Myth

A normal BMI means you're healthy

✓ Fact

BMI does not measure body fat or fat distribution, so a normal-range result does not establish an individual health assessment.

✕ Myth

BMI thresholds are the same globally

✓ Fact

Asian populations face higher health risks at lower BMI values. WHO recommends lower cutoffs (23 for overweight) for Asian populations.

✕ Myth

Muscle mass doesn't affect BMI

✓ Fact

Muscle is denser than fat. Athletes and bodybuilders frequently score “overweight” or “obese” BMI despite minimal body fat percentages.

❓ Frequently Asked Questions

What is the adult BMI reference range?+

The standard normal-weight adult screening category is 18.5 to below 25. That category is a population reference, not proof of individual health, and clinicians may consider body composition, medical history, pregnancy, and other measures.

How is BMI calculated?+

BMI is calculated by dividing your weight in kilograms by your height in metres squared. Formula: BMI = weight (kg) ÷ height² (m²). In imperial units: BMI = (weight (lbs) × 703) ÷ height² (in²). For example, a person weighing 70 kg at 1.75 m has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.

What do the BMI categories mean?+

Adult BMI screening categories are underweight (below 18.5), normal weight (18.5 to below 25), overweight (25 to below 30), Class I obesity (30 to below 35), Class II obesity (35 to below 40), and Class III obesity (40 or above). These categories do not diagnose a condition or establish an individual’s health risk, treatment, or urgency.

Is BMI accurate for athletes?+

BMI does not distinguish muscle from fat, so it may classify some muscular athletes in higher weight categories without describing their body composition. A clinician or qualified sports-health professional may consider waist measurements or an appropriate body-composition assessment alongside BMI.

How does BMI differ for men vs. women?+

Standard adult BMI thresholds do not change by sex, but BMI does not measure sex-related differences in body composition. That limitation is one reason BMI should not be interpreted as a direct body-fat measurement.

Does a BMI category mean I should lose weight?+

No BMI value by itself determines whether an individual should lose weight. A qualified clinician or registered dietitian can interpret BMI alongside medical history, symptoms, body composition, waist circumference, laboratory results, medications, and personal goals.

Can BMI be used for children?+

People ages 2–19 require BMI-for-age percentiles based on age and sex. This fixed-category adult calculator is intended for people aged 20 and older; use an authoritative child and teen BMI resource for younger users.

What does Class III obesity mean in BMI categories?+

Class III obesity is the adult BMI category at or above 40. This screening category does not by itself determine individual health risk, urgency, medication use, or eligibility for a procedure; those decisions require a qualified clinician to consider the person’s broader health context.

How accurate is BMI for South Asian populations?+

Some clinical guidance uses additional BMI action points for Asian populations because population-level associations can differ. Applicable thresholds depend on the guideline and jurisdiction, so discuss population-specific interpretation with a qualified clinician.

What is BMI Prime?+

BMI Prime divides BMI by 25, the exclusive upper boundary of the standard adult normal-weight category used by this calculator. It is another expression of the same screening result and does not add an individualized health assessment.

Can BMI be used during pregnancy?+

BMI calculated from weight during pregnancy does not account for pregnancy-related changes in body composition and fluid. Use maternity-care guidance and discuss questions with a qualified healthcare professional.

Can a low BMI be dangerous?+

A BMI below 18.5 is associated at a population level with some health risks, but BMI alone cannot identify a cause or diagnose a condition. If the result is unexpected or accompanied by symptoms or unintentional weight change, consider discussing it with a qualified clinician.

Should I use BMI to track weight loss progress?+

BMI can be one trend measure, but it does not directly measure body fat, muscle mass, or individual health. A qualified clinician or registered dietitian can help select appropriate measures based on your health context and goals.

What makes an online BMI calculator accurate?+

An accurate BMI calculator correctly applies the standard formula — weight (kg) ÷ height² (m²) — the same reference calculation used by major health organizations worldwide, consistently across metric and imperial units. That correctness is a matter of accurate arithmetic, not medical accuracy: BMI itself is a population screening measure, so no BMI calculator, however precise the math, can diagnose an individual’s health or replace an assessment from a qualified clinician.

References & Further Reading

1.WHO Expert Consultation (2004). Appropriate body-mass index for Asian populations. The Lancet, 363(9403), 157–163. View ↗
2.Keys A, et al. (1972). Indices of relative weight and obesity. Journal of Chronic Diseases, 25(6), 329–343. View ↗
3.Berrington de Gonzalez A, et al. (2010). Body-Mass Index and Mortality. NEJM, 363, 2211–2219. View ↗
4.World Health Organization. (2021). Obesity and overweight. WHO Fact Sheet. View ↗
5.National Institutes of Health. (1998). Clinical guidelines on identification, evaluation, and treatment of overweight and obesity in adults. View ↗
6.Centers for Disease Control and Prevention. (2022). About Adult BMI. View ↗

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BMI Calculator

Free BMI Calculator with instant results. Calculate your Body Mass Index, get your ideal weight range, and receive AI-powered health recommendations.

Methodology, sources & limitations

This calculator uses a published formula and the values entered in the calculator to generate the result.

Formula: BMI = weight(kg) / height(m)²
Jurisdiction & units: Intended for US, IN, EU, GB, AU, CA, Global. Supports both units where applicable.
Assumptions & limitations: Results are screening or educational estimates based on the inputs you provide. They do not diagnose, treat, or replace advice from a qualified clinician.
Review status: Formula and automated QA completed September 9, 2026; independent professional review is pending. Next scheduled review: December 9, 2026.

Validation sources

CDC Growth Charts
WHO Global Database on BMI

BMI Calculator — Answer & Method

Calculate adult Body Mass Index with the standard weight-to-height formula. Supports metric and US units and shows adult screening categories, BMI Prime, and a reference weight range.

Formula: Body Mass Index

BMI = weight(kg) / height(m)²

w = Weight (kg)

h = Height (m)

Example Calculation

A person weighing 70 kg at 1.75 m tall has a BMI of 22.86, classified as Normal weight by WHO standards.

Important limitation

This is an educational estimate, not a diagnosis or a substitute for professional medical advice.

Key Facts

BMI is calculated as weight in kilograms divided by height in meters squared.
WHO classifies BMI below 18.5 as underweight, 18.5-24.9 as normal, 25-29.9 as overweight, and 30+ as obese.
BMI does not directly measure body fat percentage.
CDC recommends BMI screening for adults aged 20 and older.

Sources & Validation

CDC Growth ChartsWHO Global Database on BMI

Related Calculators

Body Fat Calculator BMR Calculator Ideal Weight Calculator Calorie Deficit Calculator

Deterministic: YesAI-Generated Numbers: NoVerified: 2026-02-12

BMI Calculator

⚖️ Details

Related Articles

BMI vs. Body Fat Percentage: Which Is Better?

How Many Calories Do You Need? TDEE & BMR

Best Free BMI Calculator in 2026: 7 Tools Tested

📊 BMI Chart

BMI Chart — Adult Categories

📜 History of BMI

📝 Worked Examples

Normal Weight

Overweight

Obese Class I

✅ Published Calculation and QA Details

⚠️ Limitations of BMI

❌ Cannot distinguish fat from muscle

❌ Does not measure body fat distribution

❌ Age-related inaccuracy

❌ Ignores bone density

❌ Pregnancy limitations

❌ Does not reflect metabolic health

🩺 Health Risks Linked to BMI Categories

Associated with higher BMI (overweight/obesity)

Associated with lower BMI (underweight)

🧒 BMI Calculator for Kids and Teens

Why kids need a different method

📊 Obesity & Overweight Prevalence: Current Data

⚖️ BMI vs. Body Fat vs. Ideal Weight

🌏 Ethnicity & BMI Adjustments

Standard WHO Cutoffs (General)

Additional Asian Population Action Points

🩺 Discussing Your BMI Result

Underweight (BMI < 18.5)

Normal Weight (18.5–24.9)

Overweight (25–29.9)

Obese (BMI ≥ 30)

🔬 Key Research on BMI

Obesity and Overweight

About Adult BMI

BMI and Mortality Risk

🔍 BMI Myths vs. Facts

❓ Frequently Asked Questions

References & Further Reading

Related Health Calculators

Explore All Health & Fitness Calculators

BMI Calculator

Methodology, sources & limitations

Validation sources

BMI Calculator — Answer & Method

Formula: Body Mass Index

Example Calculation

Important limitation

Key Facts

Sources & Validation

Related Calculators

Related Articles

BMI vs. Body Fat Percentage: Which Is Better?

How Many Calories Do You Need? TDEE & BMR

Best Free BMI Calculator in 2026: 7 Tools Tested

See Also

Body Fat Calculator

Waist-to-Height Ratio

Ideal Weight Calculator

BMI Health Guide

What people are saying

BMI Calculator

⚖️ Details

Related Articles

BMI vs. Body Fat Percentage: Which Is Better?

How Many Calories Do You Need? TDEE & BMR

Best Free BMI Calculator in 2026: 7 Tools Tested

📊 BMI Chart

BMI Chart — Adult Categories

📜 History of BMI

📝 Worked Examples

Normal Weight

Overweight

Obese Class I

✅ Published Calculation and QA Details

⚠️ Limitations of BMI