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Ideal Weight Calculator

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How It Works

Ideal Body Weight (IBW) is a target derived from height (and sex) by one of four classic formulas — Hamwi (1964), Devine (1974), Robinson (1983), and Miller (1983). Each formula starts from a base weight at 5 ft and adds (or subtracts) a per-inch increment for every inch above (or below) 5 ft. None of the four is "the" right answer: they were derived in different eras for different clinical purposes, and they disagree by several kilograms at the same height. This page shows all four side-by-side so you can see the spread.

Example Problem

A 5'10" (70 in) male asks for his ideal body weight. The delta over 5 ft is 70 − 60 = 10 inches. Compute all four formulas.

  1. Identify the inputs: sex = male, height = 70 in, delta over 5 ft = 10 in.
  2. Hamwi: 48 + 2.7 × 10 = 75 kg ≈ 165 lb.
  3. Devine: 50 + 2.3 × 10 = 73 kg ≈ 161 lb.
  4. Robinson: 52 + 1.9 × 10 = 71 kg ≈ 156 lb.
  5. Miller: 56.2 + 1.41 × 10 = 70.3 kg ≈ 155 lb.
  6. Range across the four: roughly 70.3–75 kg, or 155–165 lb — none is the single "true" target.

Key Concepts

Hamwi (1964) was published by Dr. George Hamwi for use by registered dietitians and is the most generous (highest target). Devine (1974) was published by Dr. B.J. Devine for gentamicin dosing in obese patients and has become the de-facto reference in pharmacy. Robinson (1983) and Miller (1983) were both published in clinical-pharmacy journals as revisions intended to better match modern population means; both produce lower targets than Hamwi and Devine. All four were derived from US adult cohorts and become unreliable for very tall (>6'4") or very short (<4'10") adults, for athletes with significant muscle mass, and for pediatric populations. For general health screening, BMI is preferred — IBW is most useful in clinical settings where a single body-size reference is needed for drug dosing.

Applications

  • Estimating a reference body size for medication dosing (the original clinical purpose of Devine).
  • Setting a rough weight target during a structured weight-loss program — paired with BMI and body-fat percentage, not used alone.
  • Comparing four published formulas side-by-side when textbooks cite different numbers.
  • Quick sanity-check against your current weight — but the spread between formulas is wide, so don't treat a single number as authoritative.

Common Mistakes

  • Treating one formula as "the" right answer. The four formulas were published for different purposes and disagree by 5+ kg at the same height — that's expected, not a bug.
  • Using IBW as a weight-loss goal without context. BMI and body-fat percentage are better individual targets; IBW is a population reference for clinical dosing.
  • Applying these formulas to children or teens. They were derived from adult cohorts and don't reflect growing bodies — use CDC/WHO growth charts instead.
  • Forgetting that the per-inch delta is signed. Heights below 5 ft subtract from the base; the math still works, but the resulting numbers should be cross-checked against clinical judgment for very short adults.
  • Reading ethnic differences as built-in. The formulas were derived from primarily White US cohorts in the 20th century and have known biases for South Asian, East Asian, and Pacific Islander populations.

Frequently Asked Questions

What is ideal body weight?

Ideal Body Weight (IBW) is a reference weight estimated from height (and sex) using a published formula. It was originally introduced as a clinical reference for drug dosing — not as a target every person should hit. Four formulas are in common use (Hamwi, Devine, Robinson, Miller), and they routinely disagree by several kilograms at the same height.

Which ideal weight formula is best?

No single formula is "the" right one. Devine (1974) is the de-facto pharmacy reference because it was published for gentamicin dosing and is widely cited in drug-dosing protocols. Hamwi (1964) is the dietitian standard. Robinson and Miller (both 1983) were intended as revisions matching modern population means. For an individual, the safer answer is the range across all four.

Why do the four formulas disagree?

They were derived in different eras (1964, 1974, 1983, 1983) from different cohorts and with different clinical purposes. Hamwi is the most generous (highest target), Miller the least. The 5+ kg spread at the same height is the honest measure of how loose the underlying concept is — there is no single correct IBW.

Does ethnicity matter for ideal body weight?

Yes, but the four classic formulas don't adjust for it. They were derived primarily from White US adult cohorts and overestimate IBW for South Asian, East Asian, and many Pacific Islander populations. For ethnicity-specific screening, lower BMI thresholds (e.g., overweight at BMI 23 for adults of South Asian descent) are recommended by several health bodies — not adjusted IBW formulas.

Should I aim for my ideal weight?

Not necessarily. IBW is a clinical reference, not a personal goal. For most adults, BMI (18.5–24.9 is the WHO Normal band) and body-fat percentage are more meaningful targets. If you're using IBW to set a weight-loss goal, pick a number inside the range across the four formulas rather than treating one as authoritative — and discuss it with a clinician.

How accurate are the Hamwi, Devine, Robinson, and Miller formulas?

All four are reasonable estimates for typical adult heights (about 5 ft to 6 ft 4 in) but become unreliable at the extremes and for athletes with high muscle mass. The spread between the four formulas (often 5+ kg at the same height) is roughly the true uncertainty — any single formula's precision should not be read as accuracy.

What is the formula for ideal body weight?

All four formulas have the same shape: IBW (kg) = base + per-inch × (height in inches − 60). The base and per-inch coefficients differ by formula and sex. Hamwi male: 48 + 2.7 × delta. Devine male: 50 + 2.3 × delta. Robinson male: 52 + 1.9 × delta. Miller male: 56.2 + 1.41 × delta. Female versions use the same shape with smaller bases and slightly smaller per-inch coefficients.

Worked Examples

Pharmacy Dosing

What is the Devine IBW for a 5'10" male (the gentamicin reference)?

A 5'10" (178 cm) adult male is admitted for IV antibiotic therapy. The pharmacy needs Devine ideal body weight to compute gentamicin dosing. What is the Devine IBW, and how does it compare to the other three classic formulas?

  • Identify the inputs: sex = male, height = 178 cm ≈ 70 in, delta over 5 ft = 70 − 60 = 10 in.
  • Apply Devine: IBW = 50 + 2.3 × 10 = 73 kg ≈ 161 lb.
  • For context, the other three at the same height: Hamwi = 75 kg (165 lb), Robinson = 71 kg (156 lb), Miller = 70.3 kg (155 lb).
  • Spread across the four: 70.3–75 kg (155–165 lb) — about 5 kg of disagreement at this height.

Devine IBW ≈ 73 kg (161 lb); range across all four ≈ 70.3–75 kg (155–165 lb)

Devine is the de-facto pharmacy reference because it was published for gentamicin dosing in 1974. For an individual patient, the range across all four formulas is a more honest representation than any single number.

Outpatient Clinic

What is the ideal weight range for a 5'4" female?

A 5'4" (163 cm) adult female asks her primary-care clinician for an ideal-weight target. The clinician wants to show the spread across the four classic formulas rather than picking one.

  • Identify the inputs: sex = female, height = 163 cm ≈ 64.2 in, delta over 5 ft ≈ 4.2 in.
  • Hamwi: 45.5 + 2.2 × 4.2 ≈ 54.7 kg (≈ 121 lb).
  • Devine: 45.5 + 2.3 × 4.2 ≈ 55.2 kg (≈ 122 lb).
  • Robinson: 49 + 1.7 × 4.2 ≈ 56.1 kg (≈ 124 lb).
  • Miller: 53.1 + 1.36 × 4.2 ≈ 58.8 kg (≈ 130 lb).
  • Range ≈ 54.7–58.8 kg (121–130 lb).

Ideal weight range ≈ 55–59 kg (121–130 lb) across the four formulas

Informational only — not a substitute for clinical judgment. For most adults BMI and body-fat percentage are better individual targets than IBW. IBW is most useful in clinical settings (drug dosing) where a single body-size reference is needed.

Short Stature

How do the formulas behave for a 4'10" adult (below the 5 ft base)?

A 4'10" (147 cm) adult male asks how the four classic IBW formulas behave at his height. Each formula's per-inch delta is signed, so heights below 5 ft subtract from the base.

  • Identify the inputs: sex = male, height = 147 cm ≈ 57.9 in, delta over 5 ft ≈ −2.1 in.
  • Hamwi: 48 + 2.7 × (−2.1) ≈ 42.3 kg.
  • Devine: 50 + 2.3 × (−2.1) ≈ 45.2 kg.
  • Robinson: 52 + 1.9 × (−2.1) ≈ 48.0 kg.
  • Miller: 56.2 + 1.41 × (−2.1) ≈ 53.2 kg.
  • Range ≈ 42.3–53.2 kg (93–117 lb) — a much wider spread than at average heights.

Range ≈ 42–53 kg (93–117 lb) — formulas disagree by ~11 kg at short stature

The four formulas were derived from US adult cohorts in the 1960s–80s and become unreliable at the extremes of height. For adults under 4'10" or over 6'4", treat any single formula's number with extra skepticism.

Ideal Body Weight Formulas

All four classic formulas share the same shape — a base weight at 5 ft plus (or minus) a per-inch increment for every inch above (or below) 5 ft. They differ only in the base and the per-inch coefficient, and in how the male and female versions are split:

IBW (kg) = base + per-inch × (height_in − 60)
Hamwi (1964) — male 48 + 2.7; female 45.5 + 2.2
Devine (1974) — male 50 + 2.3; female 45.5 + 2.3
Robinson (1983) — male 52 + 1.9; female 49 + 1.7
Miller (1983) — male 56.2 + 1.41; female 53.1 + 1.36

Where:

  • IBW — Ideal Body Weight in kilograms
  • base — formula- and sex-specific kilogram base at 5 ft (60 in)
  • per-inch — formula- and sex-specific kg increment per inch over 5 ft
  • height_in — total height in inches; values below 60 produce a signed (negative) delta

None of these is "the" correct answer. Devine is the de-facto pharmacy reference because it was published for gentamicin dosing in 1974. Hamwi was published in 1964 for dietitian use and is the most generous (highest target). Robinson and Miller were published in 1983 as revisions intended to better match modern population means. All four were derived from US adult cohorts and become unreliable at the extremes of height, for athletes with significant muscle mass, and for non-US populations. For general health screening, BMI and body-fat percentage are better individual targets than IBW. This calculator is informational only and is not a substitute for clinical judgment.

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