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Peterson Ideal Body Weight Calculator

A modern, sex-neutral ideal weight equation: pick a target BMI and see the matching body weight.

How it is calculated

The tool applies the Peterson equation, which is the same for men and women: IBW = 2.2 × BMI + 3.5 × BMI × (height − 1.5), with height in metres (typed in centimetres) and BMI in kg/m². A higher target BMI raises the weight proportionally. If the target BMI is left empty or zero, the tool uses 22; values below 10 or above 40 show no result, and so do heights outside 50 to 272 cm. Alongside the ideal weight in kg and in pounds (kg × 2.20462) it prints a range: the same equation evaluated at a BMI of 18.5 and at 24.9. The equation is meant for adults, so small heights give implausibly low weights, and below about 88 cm it returns nothing. Age, muscle mass and frame size are not part of the formula.

Worked example

Height 170 cm (1.70 m), target BMI 22. The height term is 1.70 − 1.5 = 0.2. IBW = 2.2 × 22 + 3.5 × 22 × 0.2 = 48.4 + 15.4 = 63.80 kg, or 63.80 × 2.20462 = 140.65 lb. The range at BMI 18.5 and 24.9 runs from 53.65 to 72.21 kg. This is not simply 22 × 1.70² = 63.58 kg; the equation has its own height correction, so the two differ slightly.

Try this example →

Common mistakes

  • Entering height in metres or feet; the field is in centimetres, and a value below 50 shows no result.
  • Assuming the result equals target BMI × height squared. The Peterson equation adds a height-dependent term, so it differs from that shortcut, especially for very tall or very short people.
  • Picking an extreme target BMI. Only 10 to 40 is accepted, and a target near either end of that range does not describe a healthy weight.
  • Treating the single ideal figure as the goal for everyone and ignoring the range line, which shows weights at BMI 18.5 to 24.9.
  • Comparing it with Devine or Hamwi results, which use sex-specific constants and a different logic.

Sources

About this calculator

The Peterson ideal body weight equation, published in 2016 in The American Journal of Clinical Nutrition, calculates ideal weight directly from height and a chosen target BMI: IBW = 2.2 × BMI + 3.5 × BMI × (height(m) − 1.5). Unlike older formulas from the 1970s and 80s (Devine, Robinson, Hamwi, Miller), which use separate constants for men and women and were derived from limited, non-representative samples, Peterson’s equation is sex-neutral and was built by working backward from a target BMI within the healthy range.

The older formulas remain in wide clinical use for drug dosing because hospitals standardized on them decades ago, but researchers have pointed out they don’t correspond cleanly to any defined BMI category, making Peterson’s approach appealing whenever the goal is genuinely “a healthy BMI for this height” rather than matching a legacy dosing convention — clinicians and researchers who want a modern, BMI-anchored reference point choose a target (commonly 22 for a mid-range healthy BMI) and let the equation solve for the matching weight.

Enter your height and a target BMI, and this calculator applies the Peterson equation to give you the corresponding ideal body weight in kilograms and pounds, plus the weight range for a BMI of 18.5 to 24.9 at your height. If you leave the BMI blank it uses 22.

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