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BMI Calculator

Calculate adult body mass index using metric or imperial measurements. BMI is a screening measure and is only one part of a broader health assessment.

Detailed optionsStep-by-step guideWorked examples
Make it yours

Imperial values are converted internally using 1 lb = 0.45359237 kg and 1 inch = 2.54 cm.

years

This adult model supports whole ages from 20 to 100. Children and teens need age-specific assessments.

kg

Use a recent weight measurement in the selected units.

cm

Enter standing height. For imperial units, enter total inches: 5 feet 9 inches = 69 inches.

Private by design. Calculated in your browser.
Your body mass indexLIVE RESULT
22.86BMI
Healthy weight
UnderweightHealthyOverweightObesity
Weight (kg)70
Height (cm)175
Adult educational estimate. See the methods and limitations below.
YOUR ANIMATED GUIDE

Follow your numbers, step by step.

These steps use your current inputs. Choose a step or play the walkthrough.

STEP 1 / 4
70 kg
1234

Use consistent measurements

Convert pounds and inches to kilograms and centimeters when needed.

Weight = 70 kg · height = 175 cm
Explore at your own pace
ONE ASSUMPTION, A DIFFERENT PERSPECTIVE

Understand the adult categories

Category boundaries use the full, unrounded BMI.

At your height, BMI 18.5 to below 25 corresponds to 56.7 kg to below 76.6 kg. Rounded mathematical reference only; this is not an individual weight target.

Adult screening reference
Adult BMI categoryBMI range
UnderweightBelow 18.5
Healthy weight18.5 to below 25
Overweight25 to below 30
Obesity · class 130 to below 35
Obesity · class 235 to below 40
Obesity · class 340 and above

Source: CDC adult BMI categories. This screening measure should be considered with other health information.

How to use this bmi calculator

This adult BMI calculator supports kilograms and centimeters or pounds and total inches, and shows the arithmetic behind the result. The category table includes the adult screening ranges; a separate height-based range shows the weights corresponding to BMI 18.5 up to, but not including, 25. That interval is a mathematical reference, not an individual target or a diagnosis.

Measure first, then calculate

Use standing height and a recent weight in the same measurement system. For imperial height, enter total inches: multiply feet by 12 and add the remaining inches. A height of 5 feet 9 inches is 69 inches. The calculator converts imperial measurements to metric internally so both systems follow the same arithmetic.

Why the square matters

BMI divides kilograms by meters squared. Centimeters must be divided by 100 before the height is squared. At 175 cm, height is 1.75 m and height squared is 3.0625 m². A 70 kg weight therefore gives 70 / 3.0625 ≈ 22.857. Squaring 175 directly would use the wrong units and give an entirely different number.

Use the result with context

The adult categories are screening ranges for people 20 and older. BMI does not directly measure body fat or separate fat from muscle, and individual interpretation can differ. Pregnancy and child or teen growth require other assessments. Discuss an individual result with a qualified health professional.

Understanding the height-based reference range

The lower boundary is 18.5 × height in meters squared; the upper boundary is 25 × height in meters squared, with the upper boundary excluded. Displayed bounds are rounded, so use the unrounded BMI when interpreting a value near a category boundary.

BMI formulas, explained

Metric BMI

BMI = kilograms ÷ meters²

Convert centimeters to meters before squaring.

Exact imperial conversion

kg = lb × 0.45359237; meters = inches × 0.0254

The commonly used 703 shortcut is rounded; this calculator uses the conversion factors above.

Height-based reference interval

18.5 × meters² ≤ weight < 25 × meters²

This interval describes the adult healthy-weight BMI category, not a personal weight recommendation.

EVERY OPTION, EXPLAINED

Know what goes into your result.

Use this reference to check units, assumptions and advanced settings.

BMI calculator input reference
Input or optionWhat it means
Measurement systemImperial values are converted internally using 1 lb = 0.45359237 kg and 1 inch = 2.54 cm.
Your ageThis adult model supports whole ages from 20 to 100. Children and teens need age-specific assessments.
Your weightUse a recent weight measurement in the selected units.
Your heightEnter standing height. For imperial units, enter total inches: 5 feet 9 inches = 69 inches.
PUT THE FORMULA TO WORK

Worked examples you can try.

Load an example into the calculator, then change one value to explore.

EXAMPLE 01

Metric measurements

70 kg and 175 cm gives BMI ≈ 22.86. The same measurements in imperial units give the same unrounded result.

EXAMPLE 02

Feet to total inches

5 feet 9 inches = 69 inches. Try 160 lb and 69 inches to practice imperial entry.

MAKE THE NUMBERS MAKE SENSE

Common mistakes to avoid

  • Entering feet as a decimal instead of total inches in imperial mode.
  • Using centimeters directly where the formula requires meters.
  • Treating the mathematical reference interval as a personal prescription.
A LITTLE MORE CLARITY

Frequently asked questions

What do the adult BMI categories mean?

For adults 20 and older: below 18.5 is underweight, 18.5 to under 25 is healthy weight, 25 to under 30 is overweight, and 30 or above is the obesity category.

Is BMI a complete measure of health?

No. BMI does not distinguish muscle from fat or account for every individual factor. These categories are for adults 20+ and are not a pregnancy assessment. Discuss personal results with a clinician.

Why does the calculator ask for age?

Age confirms the adult scope. Age itself is not a variable in the adult BMI formula.

Does changing units change my result?

Switching units converts the current measurements. The calculated BMI should remain the same apart from a small display-rounding difference.

Why might a rounded value appear at a boundary?

Classification uses the full internal value. A result just under 25 may display as 25.00 while still being below the boundary.

Methodology & assumptions

Calculations run in your browser using the formulas and assumptions explained on this page. Intermediate values retain full floating-point precision; displayed amounts are rounded. Health results are adult educational estimates and do not replace an individual clinical or nutrition assessment. Sharing an input link places those inputs in the URL.

Further reading:CDC adult BMI categories and scope
KEEP EXPLORING

A little more perspective.

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