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Obesity Calculator

HealthHeight, Weight and Growth
Units
Sex

Sets the waist cut-offs only; BMI classes are the same for both.

Measured midway between the lowest rib and the top of the hip bone.

BMI —
WHO class
—
Weight against the obesity line
—
Waist-related risk
—
Waist-to-height ratio
—
BMI against the WHO obesity classes
The chart appears with your result

Adult obesity is defined by the WHO as a BMI of 30 or more, split into class I (30–34.9), class II (35–39.9) and class III (40 and above). A man 175 cm tall weighing 95 kg has a BMI of 31.0, class I; a 104 cm waist adds substantially increased risk.

About this tool

Clinicians grade obesity in two ways: by BMI class and by where the fat sits. This calculator does both. From height and weight it gives the BMI, the WHO class from pre-obesity through class III, and the weight that would put your height exactly on the BMI 30 line, shown as a gap above or below it. Add a waist measurement and it applies the WHO waist cut-offs for your sex (94 and 102 cm for men, 80 and 88 cm for women) and the waist-to-height ratio, where 0.5 or more points to central fat. These are screening numbers for adults; they cannot separate fat from muscle, and they are not used for children, whose weight is judged on growth percentiles.

How to use it

  1. Pick units and sex

    Metric uses cm and kg, US uses feet, inches and pounds. Sex only changes the waist cut-offs.

  2. Enter height and weight

    The BMI, WHO class and distance from the BMI 30 line appear as you type.

  3. Add your waist

    Optional. With it, the result adds the waist risk level and the waist-to-height ratio.

  4. Read the scale and working

    The chart places your BMI on the obesity classes, and the steps show each division.

Examples

5 ft 5 in, 150 lb

Units
US (lb, ft, in)
Sex
Female
Height
5
and
5
Weight
150

Result BMI: 25.0
WHO class: Overweight (pre-obesity)
Weight against the obesity line: 30.3 lb below BMI 30
Waist-related risk: Not entered
Waist-to-height ratio: —

  1. Weight = 68.04 kg, height = 1.651 m
  2. BMI = 68.04 ÷ 1.651² = 25 → Overweight (pre-obesity)
  3. Obesity threshold (BMI 30) at this height = 30 × 1.651² = 180.3 lb

A BMI of 25.0 sits at the start of pre-obesity, and about 30 lb short of the BMI 30 line for this height.

Man, 175 cm, 95 kg, 104 cm waist

Units
Metric (kg, cm)
Sex
Male
Height
175
Weight
95
Waist (optional)
104

Result BMI: 31.0
WHO class: Obesity class I
Weight against the obesity line: 3.1 kg above BMI 30
Waist-related risk: Substantially increased
Waist-to-height ratio: 0.59

  1. Weight = 95 kg, height = 1.75 m
  2. BMI = 95 ÷ 1.75² = 31 → Obesity class I
  3. Obesity threshold (BMI 30) at this height = 30 × 1.75² = 91.9 kg
  4. Waist 104 cm vs WHO cut-offs 94 / 102 cm (male) → Substantially increased
  5. Waist-to-height = 104 ÷ 175 = 0.59 (0.5 or more: central fat raised)

BMI 31.0 is obesity class I, and a 104 cm waist is past the 102 cm WHO cut-off for men.

Woman, 160 cm, 70 kg, 85 cm waist

Units
Metric (kg, cm)
Sex
Female
Height
160
Weight
70
Waist (optional)
85

Result BMI: 27.3
WHO class: Overweight (pre-obesity)
Weight against the obesity line: 6.8 kg below BMI 30
Waist-related risk: Increased
Waist-to-height ratio: 0.53

  1. Weight = 70 kg, height = 1.6 m
  2. BMI = 70 ÷ 1.6² = 27.3 → Overweight (pre-obesity)
  3. Obesity threshold (BMI 30) at this height = 30 × 1.6² = 76.8 kg
  4. Waist 85 cm vs WHO cut-offs 80 / 88 cm (female) → Increased
  5. Waist-to-height = 85 ÷ 160 = 0.53 (0.5 or more: central fat raised)

BMI is below 30, but an 85 cm waist is between the 80 and 88 cm female cut-offs and the ratio is above 0.5.

How it is calculated

BMI = weight (kg) ÷ height (m)²; obesity line = 30 × height (m)²; WHtR = waist ÷ height

weight
body mass in kg; pounds × 0.45359237
height
height in metres; inches × 0.0254
waist
waist circumference in cm; inches × 2.54

BMI is placed in the WHO adult classes: 25 to 29.9 pre-obesity, 30 to 34.9 class I, 35 to 39.9 class II, 40 and over class III. The weight at BMI 30 for your height is compared with your actual weight. A waist at or above 94 cm (men) or 80 cm (women) is increased risk, and at or above 102 cm or 88 cm substantially increased, per the WHO expert consultation. A waist-to-height ratio of 0.5 or more is the NICE flag for central adiposity.

Sources

When not to use it

  • Children and teenagers are assessed on BMI-for-age percentiles, not adult classes.
  • During pregnancy, weight and waist change for reasons unrelated to body fat.
  • Very muscular people can reach BMI 30 with little excess fat; the waist reading is more telling for them.

Common mistakes

  • Measuring the waist at the navel or over clothing instead of midway between rib and hip bone.
  • Treating BMI class I as the same risk for everyone regardless of waist size.
  • Entering height in metres into the centimetre field.

Frequently asked questions

What BMI counts as obesity?

For adults, the WHO and CDC define obesity as a BMI of 30 or higher. Class I runs from 30 to 34.9, class II from 35 to 39.9, and class III, sometimes called severe obesity, starts at 40.

Why does the calculator ask for waist size?

Fat stored around the abdomen is linked to type 2 diabetes and heart disease more strongly than fat elsewhere. Two people with the same BMI can carry very different amounts of it, and the waist measurement captures that difference.

What are the waist cut-offs for men and women?

The WHO uses 94 cm (about 37 in) for increased risk and 102 cm (about 40 in) for substantially increased risk in men. For women the figures are 80 cm (31.5 in) and 88 cm (34.6 in). Some populations, including South Asian adults, have lower national cut-offs.

What does a waist-to-height ratio of 0.5 mean?

It means the waist is half the height. NICE guidance uses 0.5 to 0.59 as increased health risk and 0.6 or more as high risk, and the ratio works the same way for men and women of any height.

Is pre-obesity the same as overweight?

Yes. The WHO uses pre-obesity for a BMI of 25 to 29.9, which the CDC and most clinics call overweight. It is a separate band from the obesity classes that start at 30.

Why is the obesity line shown as a weight?

Turning BMI 30 back into kilograms or pounds for your height makes the threshold concrete. At 175 cm the line is 91.9 kg, so someone at 95 kg is about 3.1 kg above it.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 9). Obesity Calculator. Tools Directory. Retrieved October 28, 2026, from https://tools.milunir.com/health/height-weight-and-growth/obesity-calculator/

MLA

Tools Directory Editorial Team. “Obesity Calculator.” Tools Directory, 9 Oct. 2026, https://tools.milunir.com/health/height-weight-and-growth/obesity-calculator/. Accessed 28 Oct. 2026.

Chicago

Tools Directory Editorial Team. “Obesity Calculator.” Tools Directory. Last modified October 9, 2026. Accessed October 28, 2026. https://tools.milunir.com/health/height-weight-and-growth/obesity-calculator/.

Link<a href="https://tools.milunir.com/health/height-weight-and-growth/obesity-calculator/">Obesity Calculator – Tools Directory</a>