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How to Calculate BMI in 2026: Formula, Chart & Healthy Ranges

Learn how to calculate BMI step by step using the metric and imperial formulas, read the WHO weight categories, and understand when BMI is and isn't a reliable indicator of health.

By Daniel Agrici Reviewed by Rahul Singh, Health Researcher

Quick Answer: BMI = weight(kg) ÷ height(m)². Example: 70kg ÷ (1.75m)² = 22.9 BMI (Healthy range: 18.5–24.9). Imperial: [weight(lbs) × 703] ÷ height(inches)². Use our Free BMI Calculator for instant results.

BMI — Body Mass Index — is the most widely used screening tool for assessing whether body weight is in a healthy range relative to height. It requires no lab test, no special equipment, and takes under a minute to calculate. Despite its simplicity, it remains the standard first-line measure used by the WHO, the CDC, and healthcare providers worldwide.

This guide explains exactly how to calculate BMI in 2026 using both the metric and imperial formulas, walks through step-by-step worked examples, explains how to read the result, and covers where BMI is reliable and where it falls short. If you want to skip the arithmetic, the BMI Calculator gives you an instant result with category labels and healthy weight estimates.

The BMI Formula

There are two versions depending on which measurement system you use.

Metric formula (kilograms and meters):

BMI = weight (kg) / height (m)²

Imperial formula (pounds and inches):

BMI = (weight in lbs × 703) / height (in)²

The 703 conversion factor accounts for the difference between the metric and imperial unit systems. Both formulas produce exactly the same BMI value for the same person — they are mathematically equivalent.

The formula squares height rather than using it directly because body mass scales non-linearly with height. A person who is twice as tall is not twice as heavy — they are roughly eight times as heavy if proportions stay constant. Squaring height (rather than using it raw, or cubing it) produces a ratio that stays roughly consistent across the range of adult heights, which is why Adolphe Quetelet settled on this form in the 1830s. Some researchers argue that an exponent of 2.5 would be slightly more accurate, but height squared strikes the practical balance between simplicity and consistency.

Step-by-Step: Imperial Calculation

Example: A person weighs 185 pounds and is 5 feet 9 inches tall.

  1. Convert height to total inches: 5 x 12 + 9 = 69 inches
  2. Square the height: 69 x 69 = 4,761
  3. Multiply weight by 703: 185 x 703 = 130,055
  4. Divide: 130,055 / 4,761 = 27.3

BMI = 27.3 — this falls in the overweight category.

Example 2: A person weighs 140 pounds and is 5 feet 5 inches tall.

  1. Height in inches: 5 x 12 + 5 = 65 inches
  2. Height squared: 65 x 65 = 4,225
  3. Weight x 703: 140 x 703 = 98,420
  4. Divide: 98,420 / 4,225 = 23.3

BMI = 23.3 — this falls in the normal weight range.

Step-by-Step: Metric Calculation

Example: A person weighs 78 kg and is 1.72 meters tall.

  1. Square the height: 1.72 x 1.72 = 2.9584
  2. Divide weight by height squared: 78 / 2.9584 = 26.4

BMI = 26.4 — overweight category.

Example 2: A person weighs 62 kg and is 1.68 meters tall.

  1. Height squared: 1.68 x 1.68 = 2.8224
  2. Divide: 62 / 2.8224 = 21.97

BMI = 22.0 — normal weight.

The metric version is more direct — no conversion factor, just divide. If you work with pounds and feet, remember to convert height entirely to inches before squaring.

BMI Categories: The 2026 Standard

The WHO adult categories have not changed in 2026. They apply to adults aged 20 and over of both sexes:

BMI RangeCategoryHealth Implication
Below 18.5UnderweightMay indicate nutritional deficiency, increased infection risk
18.5 — 24.9Normal weightAssociated with lowest all-cause mortality in most populations
25.0 — 29.9OverweightElevated risk for metabolic conditions, cardiovascular disease
30.0 — 34.9Obesity Class ISignificant risk; medical evaluation recommended
35.0 — 39.9Obesity Class IIHigh risk; weight management intervention strongly advised
40.0 and aboveObesity Class IIIVery high risk; associated with severe comorbidities

For a quick result with these category labels applied automatically, use the BMI Calculator.

Working Backwards: Finding Your Healthy Weight Range

The BMI formula can be reversed to find the weight range that falls within the normal category for a given height. This gives a concrete target rather than an abstract number.

Formula: Weight = BMI x height (m)² or Weight (lb) = BMI x height (in)² / 703

Example: What is the healthy weight range for someone who is 5 feet 8 inches (68 inches) tall?

Lower bound (BMI = 18.5): 18.5 x 68² / 703 = 18.5 x 4,624 / 703 = 121.6 lbs

Upper bound (BMI = 24.9): 24.9 x 4,624 / 703 = 163.8 lbs

A 5’8” adult falls within the normal BMI range between approximately 122 and 164 pounds. The BMI Calculator shows this range automatically alongside your calculated BMI.

How BMI Varies by Population

BMI does not carry identical meaning for everyone. Three key variables shift how the number should be interpreted.

Sex: Women naturally carry more essential body fat than men. At the same BMI, women tend to have a higher body fat percentage than men. This does not change the cutoffs, but it does mean a woman at BMI 24 may have a different health profile than a man at the same value.

Age: Older adults typically lose muscle mass while gaining fat, a process called sarcopenia. This means a 70-year-old with a BMI of 24 may carry more fat and less lean tissue than a 30-year-old with the same number. Some research suggests that a slightly higher BMI in the 25-27 range may be associated with better survival outcomes in adults over 65, possibly because modest fat reserves aid recovery from illness.

Ethnicity: People of South Asian and East Asian descent tend to develop metabolic complications — insulin resistance, type 2 diabetes, cardiovascular disease — at lower BMI values than those of European descent. The WHO has noted that the overweight threshold for some Asian populations may be more appropriately set at 23 rather than 25. Pacific Islander populations, who often have higher bone density and muscle mass, may tolerate higher BMI values without equivalent metabolic risk.

Children and teens: Adult BMI categories do not apply to anyone under 20. For younger people, BMI must be plotted on age-and-sex-specific growth percentile charts. The CDC defines overweight as at or above the 85th percentile and obesity as at or above the 95th percentile for age and sex.

Where BMI Falls Short

BMI is a useful screening tool, but it has well-documented limitations that are worth understanding.

It cannot distinguish fat from muscle. A professional rugby player, an Olympic weightlifter, or a serious recreational athlete may have a BMI of 28 or 29 due to high muscle mass while carrying very little body fat. BMI would flag them as overweight — clearly a misleading signal. For anyone who trains with weights regularly, body fat percentage is a far more meaningful metric. The Body Fat Calculator provides a more nuanced picture.

It ignores fat distribution. Visceral fat — the fat stored around internal organs in the abdominal region — is far more metabolically dangerous than subcutaneous fat stored under the skin. Two people can share the same BMI while having very different fat distributions. Waist circumference is a useful complement: the CDC suggests that a waist above 40 inches (men) or 35 inches (women) indicates elevated risk regardless of BMI.

It can miss normal-weight obesity. People with a BMI below 25 can still carry a high proportion of visceral fat — a condition sometimes called metabolically obese normal weight. Elevated fasting glucose, high triglycerides, or blood pressure concerns may be present even when the BMI looks fine.

It is less accurate at the extremes of height. Very tall people tend to have BMI underestimated; very short people tend to have it overestimated. This is a known mathematical property of the height-squared formula.

BMI Alongside Other Health Metrics

The most reliable picture of metabolic health comes from combining BMI with complementary measures:

MetricWhat It MeasuresWhere to Calculate
Body fat percentageFat vs lean tissue ratioBody Fat Calculator
Waist circumferenceAbdominal fat accumulationTape measure at navel
BMRResting calorie needsBMR Calculator
TDEETotal daily calorie burnCalorie Calculator
Waist-to-hip ratioFat distribution patternTape measure

When BMI, body fat percentage, and waist circumference are all within healthy ranges, the odds of metabolic disease are substantially lower than when any single measure is used alone.

Frequently Asked Questions

Q: What is a healthy BMI for a woman in her 40s?

The standard WHO healthy range of 18.5 to 24.9 applies, but context matters. Women in their 40s are often in or approaching perimenopause, which is associated with changes in fat distribution — particularly an increase in abdominal fat — even without significant weight change. A BMI within the normal range does not rule out rising visceral fat, so waist circumference and routine blood work (especially fasting glucose and lipid panels) are worth tracking alongside BMI during this period.

Q: Is BMI still used by doctors in 2026?

Yes, BMI remains the most widely used clinical screening tool for weight status. In 2023, the American Medical Association (AMA) issued guidance recommending that BMI be used in conjunction with other measures rather than as a standalone diagnostic. Most clinical guidelines still use BMI as the starting point for conversations about weight-related health, while increasingly pairing it with waist circumference, body fat percentage, and metabolic markers for a fuller assessment.

Q: Does BMI account for bone density?

No. BMI treats all weight the same regardless of whether it comes from fat, muscle, water, or bone. People with naturally high bone density — which is more common in certain ethnic groups and in people who have done significant weight-bearing exercise over their lifetime — may have a higher BMI without any excess fat. This is one reason why BMI should not be used as the sole basis for clinical decisions.

Q: How accurate is online BMI calculation?

A BMI calculator that uses the standard WHO formula will give a mathematically accurate result provided you enter your height and weight correctly. The accuracy question is really about what that number means for your individual health — which depends on age, sex, ethnicity, muscle mass, and fat distribution in ways that no formula can fully capture. Use the number as a starting point, not a verdict.

Q: At what BMI should someone see a doctor?

The CDC recommends that adults with a BMI below 18.5 or 30 and above consult a healthcare provider. If BMI falls in the overweight range (25 to 29.9) and is accompanied by other risk factors — high blood pressure, family history of type 2 diabetes, elevated cholesterol — a medical conversation is also warranted. Ultimately, any concerns about weight or metabolic health are worth discussing with a doctor regardless of BMI category.

Sources

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Daniel Agrici

NovaCalculator Editorial Team

Our writers combine mathematical expertise with clear writing to make calculations accessible to everyone. Content is peer-reviewed for accuracy against authoritative sources including NIST, WHO, and CFPB.

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