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BMI calculator: adult BMI and reference chart

Calculate an adult body mass index from height and weight, then see carefully framed international reference bands and height-specific boundary weights.

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Calculate your result

Enter your current measured weight.

Accepted range: 10 to 500 kg

Enter standing height without shoes.

Accepted range: 50 to 275 cm

Your result will appear here

Nothing is saved or added to the URL.

What this result means

BMI divides weight in kilograms by height in metres squared. Public-health guidance uses BMI as one adult screening measure and notes that it does not directly measure body fat or explain a person's whole health picture. [1][4][5]

International adult BMI reference bands

Published adult BMI references use these boundaries: below 18.5; 18.5 to below 25.0; 25.0 to below 30.0; 30.0 to below 35.0; 35.0 to below 40.0; and 40.0 or more. [1]

CDC describes adult BMI as a screening measure and notes that BMI does not measure body fat or health directly. [1]

LongevityMate assigns the reference label from the exact unrounded result. A displayed value near a boundary can therefore look the same after rounding while belonging to a different exact band. The labels are presented only as reference context, not as a diagnosis or personal weight judgement.

What the height-specific weight points show

Each displayed weight point is the exact weight that gives BMI 18.5, 25.0, 30.0, 35.0 or 40.0 at the entered height, rounded once for display in the selected units. It is a personalized chart lookup, not an ideal weight, target or instruction to gain or lose weight.

Formula and unit basis

Adult BMI is weight in kilograms divided by height in metres squared. [1]

NIST defines one pound as exactly 0.45359237 kilograms and one inch as exactly 0.0254 metres. [2]

LongevityMate applies those factors with exact decimal arithmetic, assigns the reference band before display rounding, and rounds the displayed BMI and height-specific boundary weights half-up to one decimal place.

What BMI cannot measure

BMI does not distinguish fat from muscle, show where body fat is carried, measure fitness or describe the whole health picture. Age, muscle mass, illness, fluid status and measurement error can change how useful it is for an individual. [1][5][6]

A waist measure may add different information for some adults, but it also has its own measurement protocol and exclusions. Do not substitute one number for a wider assessment. [4][5]

Why regional and personal context matters

Some UK and New Zealand guidance notes that people from certain Asian, Black African, African-Caribbean, Middle Eastern, Pacific or Māori backgrounds may experience health risk at different BMI levels. [4][7]

Canada also advises that age, ethnicity, muscularity and other factors can affect individual interpretation. A reference band is therefore context, not a final health judgement. [6]

The CDC adult BMI categories apply from age 20, while NHS, Health Canada and Health New Zealand adult guidance applies from age 18. [1][4][6][7]

LongevityMate limits this route to adults aged 18 and older. It does not collect ethnicity, silently change thresholds or provide country-specific clinical advice; follow local clinical guidance when interpretation matters.

Measure consistently

Use a current weight and standing height without shoes. Recheck an unexpected result before interpreting a small change, because scale accuracy, clothing, posture and height entry can affect the calculation. [1][4]

A calm next step

Use BMI as one piece of general context. If the result is unexpected, changes quickly, or raises a health or eating concern, discuss the wider picture with a qualified clinician rather than acting on this calculator alone. [1][4]

Formula and assumptions

Formula
BMI = kg ÷ m²
Version
Adult body mass index, adult-bmi-exact-unit-v1
Rounding
Convert pounds and inches to SI with exact factors, calculate BMI with exact decimal rational arithmetic, choose the reference band from the unrounded result, and round only the displayed BMI and height-specific boundary weights to one decimal place using half-up rounding.
Worked example
For 70.0 kg and 170.0 cm, height is 1.70 m and BMI is 70 ÷ 1.70² = 24.221453…. The displayed result is 24.2, while the exact unrounded result selects the 18.5-to-below-25.0 international adult reference band. At 170.0 cm, the BMI 25.0 boundary weight is 72.25 kg, displayed as 72.3 kg; it is a chart boundary, not a personal target.

Who this is for — and when not to use it

Intended use

Adults aged 18 years and older who want a transparent body mass index and a height-specific view of international adult BMI reference boundaries for general education.

Not intended for

This tool does not diagnose health, measure body fat, set a healthy or ideal weight, calculate calories, prescribe weight change, assess children or teenagers, or replace individualized clinical assessment.

Exclusions

  • Anyone under 18 years old; children and teenagers require age- and sex-specific growth references
  • Pregnancy
  • A diagnosed or suspected eating disorder, or use that could reinforce body checking
  • A condition that materially affects standing height
  • Amputation, substantial oedema or fluid retention, severe skeletal differences, or another situation where standard BMI interpretation is unsuitable
  • Diagnosis, treatment decisions, fitness clearance, body-fat estimation, ideal-weight targets or personal risk prediction

Evidence sources

  1. 1. Adult BMI categories — US Centers for Disease Control and Prevention. Accessed Aug 17, 2026.
  2. 2. NIST Guide to the SI, Appendix B conversion factors — National Institute of Standards and Technology. Accessed Aug 17, 2026.
  3. 3. Obesity and overweight fact sheet — World Health Organization. Accessed Aug 17, 2026.
  4. 4. Calculate your body mass index for adults — NHS. Accessed Aug 17, 2026.
  5. 5. Body mass index and waist circumference — Australian Government Department of Health, Disability and Ageing. Accessed Aug 17, 2026.
  6. 6. Canadian guidelines for body weight classification in adults: questions and answers — Health Canada. Accessed Aug 17, 2026.
  7. 7. Healthy weight and BMI calculator — Health New Zealand. Accessed Aug 17, 2026.