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BMI Calculator: Check Your Body Mass Index

Check your Body Mass Index

HealthBy Numora health teamReviewed by Numora editorial review board, Registered Dietitian (RD)Updated Peer-reviewed

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Reviewed against primary sources.

Assumptions
kg
cm
Your BMI
Enter your values

Fill in the 2 fields above to see your result.

BMI is a screening tool only. Consult a healthcare professional for individual advice.

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⚡ The answer

BMI (body mass index) is weight divided by height squared, in kilograms per square metre. It's a rough population-level indicator of whether an adult's weight is in a healthy range — useful for tracking trends, not for diagnosing individuals, since it doesn't distinguish muscle from fat.

Quick takeaway

BMI (Body Mass Index) is a widely used screening tool for adults, calculated by dividing weight in kilograms by the square of height in meters. It quickly categorizes individuals into underweight, healthy weight, overweight, or obese ranges, providing a general indicator of potential health risks. However, BMI has limitations; it does not directly measure body fat or differentiate between muscle and fat mass, meaning highly muscular individuals might have a high BMI without excess body fat. Therefore, it should be interpreted as a preliminary assessment, not a definitive health diagnosis. Always consult a healthcare professional for a comprehensive evaluation and personalized health advice.

What is a bmi?

Use this BMI calculator to quickly determine your Body Mass Index (BMI) based on your height and weight, and identify which adult healthy-weight band you fall into. BMI serves as a valuable initial screening tool, widely adopted for population-level health assessments and trend tracking. While it offers a convenient snapshot, it's crucial to remember that BMI does not directly measure body fat or distinguish between muscle and fat mass. Therefore, it should be interpreted as a preliminary indicator rather than a definitive health diagnosis. This calculator aligns with the World Health Organization's adult BMI classifications and the Centers for Disease Control and Prevention's Healthy Weight clinical guidance, providing a reliable starting point for understanding your weight status.

The formula

BMI = weight(kg) / height(m)^2

Source: World Health Organization (WHO) Adult BMI Classification.

Worked examples

1Office worker, healthy weight range

Inputs
weight: 70height: 175
Walkthrough

A 70 kg person who is 175 cm tall has a BMI of 22.9, which sits comfortably in the Healthy weight band (18.5–25). This is close to the statistical midpoint of the healthy range, so there is meaningful buffer before either threshold. That said, BMI alone doesn't rule out elevated waist circumference or poor metabolic markers — a routine check-up remains worthwhile even at a 'good' number.

2Heavier build near the Obese threshold

Inputs
weight: 100height: 170
Walkthrough

At 100 kg and 170 cm the BMI is 34.6, placing this person in the Obese category (≥30). At this level, clinical guidelines typically recommend discussing weight management with a GP, as risk of type 2 diabetes and cardiovascular disease rises noticeably above a BMI of 30. However, if this person is a strength athlete with substantial muscle mass, a body-composition scan would give a more accurate picture than BMI alone. The number flags a conversation worth having — it doesn't close it.

3Older adult, normal BMI but potential for sarcopenia/normal-weight obesity

Inputs
weight: 65height: 165
Walkthrough

An older adult at 65 kg and 165 cm has a BMI of 23.9, placing them in the 'Healthy weight' category. While this number seems ideal, BMI alone doesn't reveal body composition changes common with aging, such as muscle loss (sarcopenia) and increased visceral fat. It's possible for an older individual to have a 'healthy' BMI but still carry health risks associated with normal-weight obesity. Regular physical activity, a protein-rich diet, and a discussion with a doctor about body composition are important for this demographic, even with a seemingly optimal BMI.

How to use this calculator

  1. Weight
  2. Height
  3. Read the result. Use the worked examples below to sanity-check against a known scenario.

What your result means and what to do next

If above
A BMI of 25.0 to 29.9 is 'Overweight', and 30.0 or higher is 'Obese'. These ranges indicate an increased risk for conditions like type 2 diabetes, heart disease, and certain cancers. Further assessment, including waist circumference and blood tests, is recommended.
If below
A BMI below 18.5 is 'Underweight'. This can be associated with nutritional deficiencies, weakened immune function, and other health concerns. Medical evaluation is advisable to determine the underlying cause and appropriate interventions.
When to escalate
If your BMI falls outside the 'Healthy weight' range, or if you have concerns about your weight, body composition, or associated health risks, consult a healthcare professional. This is especially important if you have existing health conditions, are experiencing symptoms, or are considering significant lifestyle changes.
Common misreading
Interpreting BMI as a direct measure of health or body fat. Highly muscular individuals may have a high BMI without excess fat, while older adults with a 'healthy' BMI might have high body fat due to muscle loss. BMI is a screening tool, not a diagnostic one.

Common mistakes and edge cases

Reading the category as a health diagnosis. A BMI of 25.3 is labelled 'Overweight', but that single data point says nothing about blood pressure, cholesterol, fitness level, or metabolic age. Studies show that 30–40% of people classified as overweight by BMI are metabolically healthy, while a similar proportion in the 'Healthy weight' band carry elevated risk factors.

Using kg/cm inputs directly without converting height to metres. The formula requires height in metres. If you feed 175 instead of 1.75 into the denominator, you get 70 ÷ (175 × 175) = 0.002 — a nonsensical result. The calculator handles the conversion automatically, but if you replicate the formula in a spreadsheet, remember to divide centimetres by 100 first.

Applying adult cut-points to children or teenagers. WHO and CDC use age- and sex-specific percentile charts for anyone under 20. A 14-year-old with a BMI of 24 might fall at the 85th percentile for their age and sex, placing them in the 'Overweight' category for children — even though 24 is squarely 'Healthy weight' on the adult scale. Never use this calculator to interpret a child's weight status.

How small changes affect your result

**Starting point (Healthy weight):** A 70 kg individual at 175 cm has a BMI of 22.9, placing them in the healthy weight range.

Moderate weight increase (+5 kg)
** Adding 5 kg shifts the BMI to 24.5, still healthy but nearing the overweight threshold of 25.0.
Moderate weight decrease (-5 kg)
** A 5 kg weight loss brings the BMI to 21.2, comfortably within the healthy range.
Slight height increase (+5 cm)
** An increase of 5 cm in height (to 180 cm) while maintaining 70 kg lowers the BMI to 21.6, still healthy.
Slight height decrease (-5 cm)
** A decrease of 5 cm in height (to 170 cm) with 70 kg raises the BMI to 24.2, still healthy but closer to overweight.
Entering overweight category
** At 80 kg and 175 cm, the BMI is 26.1, placing the individual in the 'Overweight' category.
Entering obese category
** A weight of 95 kg at 175 cm results in a BMI of 31.0, which is classified as 'Obese'.
Muscular build (high BMI, but not necessarily high fat)
** A 95 kg person at 180 cm has a BMI of 29.3 ('Overweight'). For a highly muscular individual, this might not indicate excess body fat, highlighting BMI's limitations.

WHO adult BMI categories with health-risk associations (ages 20+)

BMI bandRange (kg/m²)CategoryCardiometabolic risk
Underweight< 18.5Below healthyIncreased — nutritional deficiency, low immunity
Healthy weight18.5 – 24.9NormalLowest baseline
Overweight25.0 – 29.9Above healthyIncreased — type 2 diabetes, hypertension
Obese class I30.0 – 34.9Obese (mild)Moderate — metabolic + cardiovascular risk
Obese class II35.0 – 39.9Obese (severe)High — surgery considered for comorbidities
Obese class III≥ 40.0Obese (extreme)Very high — bariatric surgery often indicated

Bands and risk associations from WHO Adult BMI Classification (2000, updated 2004). For Asian populations the WHO recommends an overweight cutoff of 23.0 kg/m² and an obese cutoff of 27.5 kg/m² to better reflect regional cardiovascular risk profiles.

Frequently asked questions

What is a healthy BMI for adults?
The WHO and CDC define the healthy range as 18.5 to 24.9. A BMI below 18.5 is classed as Underweight, 25–29.9 as Overweight, and 30 or above as Obese. These thresholds apply to adults of all ages but were calibrated on predominantly European populations — some Asian health authorities use lower cut-offs (≥23 for overweight).
Is BMI accurate for muscular people?
No — BMI cannot distinguish muscle from fat. A 180 cm powerlifter at 100 kg would register a BMI of 30.9 (Obese), even with very low body fat. If you are highly muscular, a DEXA scan, hydrostatic weighing, or waist-to-height ratio gives a more accurate picture of body composition.
How do I convert pounds and inches to use this calculator?
Divide your weight in pounds by 2.2046 to get kilograms. Multiply your height in feet by 30.48, or your height in inches by 2.54, to get centimetres. For example, 154 lb ÷ 2.2046 ≈ 70 kg; 5 ft 9 in = 69 in × 2.54 = 175 cm.
Can I use this BMI calculator for children?
No. Children's bodies are still developing, so the same BMI number means different things at different ages and for different sexes. Paediatricians use age- and sex-specific growth charts where BMI is expressed as a percentile. Use a dedicated paediatric BMI tool, or ask your child's doctor.
Does BMI change with age?
The formula is the same at every age, but body composition shifts across a lifetime — older adults tend to lose muscle and gain fat without their weight necessarily changing. This means a 65-year-old and a 25-year-old with identical BMIs may have very different fat percentages. Waist circumference becomes an especially useful companion measure in older adults.
What should I do if my BMI is in the Obese range?
Start by speaking with a GP or registered dietitian rather than acting on a single number. They can contextualise BMI alongside blood pressure, blood glucose, cholesterol, physical activity level, and other factors. Sustainable changes to diet and activity are better supported with professional guidance than self-directed intervention based on BMI alone.
How is BMI calculated?
BMI is weight in kilograms divided by height in meters squared (kg ÷ m²). For US units, the formula is (weight in pounds × 703) ÷ (height in inches²). The result is a number — typically between 15 and 50 for adults — that's compared to standard ranges to flag possible underweight, healthy weight, overweight, or obesity status.
What is the normal BMI range?
The World Health Organization defines adult BMI bands as: underweight below 18.5, healthy weight 18.5–24.9, overweight 25.0–29.9, and obesity 30 or higher. These ranges apply to adults aged 20 and over. The CDC uses the same thresholds for US clinical screening.

BMI glossary

Body Mass Index (BMI)
A number calculated from weight divided by height squared (kg/m²), used as a population-level proxy for body fatness in adults.
Waist circumference
The distance around the narrowest part of the torso, measured in centimetres or inches. It captures central (abdominal) fat more directly than BMI and is often used alongside it to refine cardiovascular risk estimates.
Visceral fat
Fat stored around internal organs in the abdominal cavity. High visceral fat is more strongly linked to metabolic disease than overall body weight, and is not captured by BMI.
Normal-weight obesity
A condition where a person has a BMI in the healthy range but an abnormally high percentage of body fat, particularly visceral fat — illustrating why BMI can miss meaningful health risk.
WHO cut-points
The internationally agreed BMI thresholds (18.5, 25, 30) set by the World Health Organization, derived from studies linking BMI ranges to disease incidence and mortality across large populations.

How we built this calculator

Methodology

BMI is calculated by dividing body weight (kg) by height in metres squared. A person who is 70 kg and 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. The WHO and CDC use four cut-points — 18.5, 25.0, and 30.0 — to define the four standard categories. These thresholds were derived from large population studies linking BMI ranges to disease risk and mortality, not from individual physiology.

This calculator was written by Numora health team and reviewed by Numora editorial review board, Registered Dietitian (RD) before publication. Both names link to full bios with verifiable credentials.

Formula source
World Health Organization (WHO) Adult BMI Classification
Last reviewed
2026-04-25
Reviewer
Numora editorial review board, Registered Dietitian (RD)
Calculation runs
Client-side only
NH
WRITTEN BY
Numora health team
NE
REVIEWED AND APPROVED BY
Numora editorial review board, Registered Dietitian (RD)
In this review:
  • Verified the formula matches World Health Organization (WHO) Adult BMI Classification (2000 (updated 2004)).
  • Confirmed the rounding rule applied by the engine: BMI is rounded to one decimal place, consistent with clinical reporting standards.
  • Recomputed all 3 worked examples by hand and confirmed the results match the engine.
  • Confirmed all 8 cited sources resolve to current pages on the issuing institution.
  • Spot-checked the sensitivity scenarios against the engine for the primary baseline inputs.

Reviewed on 2026-04-25 · Next review: 2026-10-25

See editorial policy

Sources & references

Every numeric assumption traces to a primary source.

  1. https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.htmlUSA
  2. https://www.who.int/data/gho/data/themes/theme-details/GHO/body-mass-indexINT
  3. https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htmUSA
  4. https://www.nhs.uk/common-health-questions/lifestyle/what-is-the-body-mass-index-bmi/UK
  5. https://www.heart.org/en/healthy-living/healthy-eating/losing-weight/about-weightUSA
  6. https://www.diabetes.org.uk/guide-to-diabetes/managing-your-diabetes/bmi-and-ethnicityUK
  7. https://easo.org/education-portal/easo-guidelines/EU
  8. https://www.canada.ca/en/public-health/services/health-promotion/healthy-living/weight-management/body-mass-index-adults.htmlCAN
  9. Numora Editorial Policy. numora.net/editorial-policy
⚠ Important

This calculator is for informational purposes only and does not constitute medical advice. Numbers shown are estimates based on the inputs you provide. Conventions and regulations vary by country. Consult a qualified healthcare provider in your country before making decisions based on these results.