How Ideal Weight Is Calculated

Summary

Ideal body weight (IBW) calculators estimate a healthy weight range based on your height and sex. Multiple formulas exist (Devine, Robinson, Miller, Hamwi), each producing slightly different results. The calculator shows the range from all formulas and compares it to the BMI-based healthy weight range (18.5-24.9), giving you a comprehensive picture of what weight range might be appropriate for your height.

How it works

Common formulas

All formulas share the same structure: a base weight for 5 feet (152.4 cm) of height, plus an increment for each additional inch.

Devine formula (1974):

• Men: 50.0 + 2.3 x (height in inches - 60)
• Women: 45.5 + 2.3 x (height in inches - 60)

Robinson formula (1983):

• Men: 52.0 + 1.9 x (height in inches - 60)
• Women: 49.0 + 1.7 x (height in inches - 60)

Miller formula (1983):

• Men: 56.2 + 1.41 x (height in inches - 60)
• Women: 53.1 + 1.36 x (height in inches - 60)

Hamwi formula (1964):

• Men: 48.0 + 2.7 x (height in inches - 60)
• Women: 45.5 + 2.2 x (height in inches - 60)

BMI-based range

A complementary approach uses BMI thresholds:

• Healthy weight range = Height(m)^2 x 18.5 to Height(m)^2 x 24.9

This gives a wider range than any single formula and is the method recommended by the NHS and WHO.

Worked example

Male, 5’10” (70 inches, 177.8 cm)

• Devine: 50.0 + 2.3 x 10 = 73.0 kg (161 lbs)
• Robinson: 52.0 + 1.9 x 10 = 71.0 kg (156 lbs)
• Miller: 56.2 + 1.41 x 10 = 70.3 kg (155 lbs)
• Hamwi: 48.0 + 2.7 x 10 = 75.0 kg (165 lbs)
• BMI range: 1.778^2 x 18.5 to 24.9 = 58.5 to 78.7 kg

The formula range (70-75 kg) falls within the BMI healthy range (58.5-78.7 kg) and represents the middle of the healthy spectrum.

Inputs explained

• Height — in cm or feet/inches
• Sex — different base values for men and women
• Frame size — some calculators allow small/medium/large frame adjustment

Outputs explained

• Ideal weight from each formula — Devine, Robinson, Miller, Hamwi
• BMI healthy range — the weight range for BMI 18.5-24.9
• Average ideal weight — the mean of all formulas
• Current weight comparison — how far you are from the ideal range

Assumptions & limitations

• These formulas were developed primarily for drug dosing (Devine for gentamicin), not for defining healthy weight goals. They were repurposed for general health use.
• They do not account for body composition. A muscular person may weigh well above the “ideal” while having healthy body fat levels.
• The formulas were derived from insurance actuarial data of predominantly white, middle-class Americans in the mid-20th century and may not be appropriate for all populations.
• Frame size significantly affects appropriate weight but is not included in most formulas.
• The BMI-based range is more flexible and is generally preferred by modern health authorities. Even within the “healthy” BMI range, optimal weight varies by individual.