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Obesity Class Calculator

Work out obesity class instantly with clear inputs, formula shown and shareable results.

About Obesity Class Calculator

The WHO classification bands BMI at 25, 30, 35 and 40. At 105 kg and 1.72 m the BMI is 35.5 - obesity class II, needing about 1.4 kg to drop into class I and 31.1 kg to reach a BMI of 25. Even a 5-10% weight loss produces meaningful metabolic improvement well before any class boundary is crossed.

Formulas

WHO classes

25 overweight, 30 class I, 35 class II, 40 class III

Weight at a target BMI

weight = target BMI x height(m)^2

Worked example

With the default values below, Obesity Class Calculator returns Body Mass Index of 35.49. Change any input above and every figure here is recalculated in your browser.

Inputs used

Body weightminimum 1 kg
105 kg
Heightminimum 100 cm
172 cm

Results

Body Mass Index
35.49 kg/m2
WHO Classification
Obesity class II
Weight Loss To The Next Class Down
1.5 kg
Weight At A BMI Of 25
74.0 kg

Step by step

  1. 1Values used
  2. 2WHO classes
  3. 3Weight at a target BMI
  4. 4Body Mass Index= 35.49 kg/m2
  5. 5WHO Classification= Obesity class II
  6. 6Weight Loss To The Next Class Down= 1.5 kg
  7. 7Weight At A BMI Of 25= 74.0 kg

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • These figures are population-average estimates, not a medical assessment or diagnosis. Body composition equations carry errors of several percentage points, and healthy ranges vary with age, ethnicity, muscularity and medical history. Discuss weight or body composition goals with a qualified clinician or dietitian.
  • This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

These figures are population-average estimates, not a medical assessment or diagnosis. Body composition equations carry errors of several percentage points, and healthy ranges vary with age, ethnicity, muscularity and medical history. Discuss weight or body composition goals with a qualified clinician or dietitian.

Frequently Asked Questions

Does moving down a class matter clinically?

The boundaries are conventions rather than biological cliffs. A 5-10% loss improves blood pressure, lipids and glycaemia regardless of class change.

Are the classes the same worldwide?

No. Several Asian countries use lowered thresholds of 23 for overweight and 27.5 for obesity, reflecting risk at lower BMI.

Related Calculators

Obesity Class Calculator – Calculate Body Mass Index