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Body Mass Index (BMI) Calculator

Assess if your weight is healthy for your height.

Metric (cm/kg)

Imperial (in/lbs)

Sex

Age (Years)

Height (cm)

Weight (kg)

Toolkit Resources

This section provides essential information and guidance to help you make the most of your Weight Management & Body Composition Toolkit.

Purpose: Estimate a healthy weight range by height, sex, and frame size.
Formulas Used (height in inches, results in kilograms):
- Hamwi Formula:
  - Men: $$48\,\text{kg} + 2.7\,\text{kg for each inch over 5 ft}$$
  - Women: $$45.5\,\text{kg} + 2.2\,\text{kg for each inch over 5 ft}$$
- Devine Formula:
  - Men: $$50\,\text{kg} + 2.3\,\text{kg for each inch over 5 ft}$$
  - Women: $$45.5\,\text{kg} + 2.3\,\text{kg for each inch over 5 ft}$$
- Robinson Formula (1983):
  - Men: $$52\,\text{kg} + 1.9\,\text{kg for each inch over 5 ft}$$
  - Women: $$49\,\text{kg} + 1.7\,\text{kg for each inch over 5 ft}$$
- Miller Formula (1983):
  - Men: $$56.2\,\text{kg} + 1.41\,\text{kg for each inch over 5 ft}$$
  - Women: $$53.1\,\text{kg} + 1.36\,\text{kg for each inch over 5 ft}$$
Frame Size Calculation:
Your body frame size is estimated using the 'r-value', which is the ratio of your height (in cm) to your wrist circumference (in cm):
$$R = \frac{\text{Height (cm)}}{\text{Wrist Circumference (cm)}}$$
- For Men:
  - Small Frame: $$R > 10.4$$
  - Medium Frame: $$9.6 \le R \le 10.4$$
  - Large Frame: $$R < 9.6$$
- For Women:
  - Small Frame: $$R > 11.0$$
  - Medium Frame: $$10.1 \le R \le 11.0$$
  - Large Frame: $$R < 10.1$$
If wrist circumference is not provided, the frame size adjustment is skipped.
Incorporating Frame Size:
After calculating the base ideal body weight from each formula, a further adjustment is made based on your estimated frame size. This refines the weight range to better reflect individual body types:
- For a Small Frame, the calculated ideal weight is reduced by 5%.
- For a Large Frame, the calculated ideal weight is increased by 5%.
- For a Medium Frame, no specific adjustment is made for frame size.
Additionally, a general $\pm5\%$ range is applied to each formula's result to provide a healthy weight range.

References:

MDCalc: Ideal Body Weight (For Hamwi, Devine, Robinson, and Miller Formulas)
National Library of Medicine (NIH) - Ideal Body Weight Formula (Discusses various formulas including Hamwi, Devine, Robinson, Miller)
Grant, J.P. (1980). *Handbook of Parenteral Nutrition*. W.B. Saunders, Philadelphia. (Primary reference for height-to-wrist ratio frame size classification)
Blackburn GL, Thornton PA. Nutritional assessment of the hospitalized patient. Med Clin North Am. 1979;63(5):1103-15. (Often cited for ideal body weight concepts and frame size)
Metropolitan Life Insurance Company. Desirable weights for men and women. Stat Bull Metropol Life Insur Co. 1959;40:1–4. (Historical basis for ideal weight ranges)

Purpose: Estimate the percentage of body weight that is fat (a more complete measure than weight alone).
U.S. Navy Method (Metric version):
Men: $$\mathrm{BF\%} = \frac{495}{1.0324 - 0.19077\log_{10}(Ws - N) + 0.15456\log_{10}(H)} - 450$$ Women: $$\mathrm{BF\%} = \frac{495}{1.29579 - 0.35004\log_{10}(Ws + Hp - N) + 0.22100\log_{10}(H)} - 450$$
All measurements must be in centimeters.
Tip: For best accuracy, measure waist at the narrowest point, hips at the widest, and neck just below the larynx. Stand relaxed, exhale gently.

Variables:

Ws = waist circumference (cm)

Hp = hip circumference (cm, women only)

N = neck circumference (cm)

H = height (cm)

Reference: Hodgdon & Beckett, 1984

3-Site Skinfold Method (Jackson & Pollock):
Men (Chest, Abdomen, Thigh): $$\mathrm{Density} = 1.10938 - 0.0008267S + 0.0000016S^2 - 0.0002574A$$ Women (Triceps, Suprailiac, Thigh): $$\mathrm{Density} = 1.0994921 - 0.0009929S + 0.0000023S^2 - 0.0001392A$$ Then use the Siri Equation: $$\mathrm{BF\%} = \frac{495}{\mathrm{Density}} - 450$$

Variables:

S = sum of 3 skinfolds (mm)

A = age (years)

Density = body density (g/cm³)

BF% = body fat percentage

Reference: Jackson & Pollock, 1978 (British Journal of Nutrition)

Note: The YMCA method uses different, simpler formulas often based on waist circumference and body weight.

Interpreting Your Body Fat Percentage

For Men:

Essential fat: 2–5%
Athletes: 6–13%
Fitness: 14–17%
Average: 18–24%
Obese: 25% and above

For Women:

Essential fat: 10–13%
Athletes: 14–20%
Fitness: 21–24%
Average: 25–31%
Obese: 32% and above

How to Use Your Result

Compare your result to the table above to see which category you fall into.
Lower percentages (below essential fat) can be dangerous for health. Most people fall in the average or fitness range.
Higher percentages (in the obese range) may increase the risk of health problems such as heart disease and diabetes.
Use this information to set realistic fitness or weight management goals. Remember, healthy body fat levels depend on age, sex, genetics, and activity level.

For medical advice or weight loss planning, consult a healthcare professional or registered dietitian.