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Ideal Weight Calculator

Calculate your ideal body weight with Devine, Robinson, Miller, and Hamwi formulas plus the healthy BMI range — shown side by side in kilograms and pounds.

Ideal weight inputs

This calculator is for informational purposes only and is not a substitute for professional medical advice. Consult a qualified healthcare provider before making changes to your diet, exercise, or health regimen.

What is ideal body weight?

Ideal body weight (IBW) is a reference weight for a given height and sex, produced by one of several historical formulas published between 1964 and 1983. None of the formulas were designed as a fitness or beauty target — they were built for clinicians who needed a reasonable weight estimate to calculate drug doses. Because they are simple and sex-specific they drifted into popular use as a rough weight goal. Read them as "a sensible neighbourhood" rather than "the exact right number".

This calculator shows all four classic formulas — Devine, Robinson, Miller, Hamwi — plus the average and the healthy weight range derived from BMI. Together they give you a window of plausible targets rather than pretending there is one correct answer.

How this calculator works

All four formulas share the same structure: a base weight at 5 ft (60 in) of height plus a per-inch increment for every additional inch. They differ only in the base and the increment.

  • Devine (1974): men 50.0 + 2.3 × inches over 5 ft; women 45.5 + 2.3 × inches over 5 ft. Published by Ben Devine in the context of gentamicin dosing.
  • Robinson (1983): men 52 + 1.9 × inches; women 49 + 1.7 × inches. A modification proposed in the American Journal of Hospital Pharmacy.
  • Miller (1983): men 56.2 + 1.41 × inches; women 53.1 + 1.36 × inches. Another AJHP modification from the same year.
  • Hamwi (1964): men 48.0 + 2.7 × inches; women 45.5 + 2.2 × inches. The oldest of the four, from George Hamwi\'s clinical guidance for diabetes care.

The calculator also reports the healthy BMI range (18.5–24.9) computed directly from your exact height. That range is wider than any single IBW number and reflects the current WHO definition of healthy adult weight.

Worked example

Take a man who is 178 cm tall. That is 70.08 inches, or 10.08 inches above 5 ft.

  • Devine: 50.0 + 2.3 × 10.08 ≈ 73.2 kg
  • Robinson: 52 + 1.9 × 10.08 ≈ 71.2 kg
  • Miller: 56.2 + 1.41 × 10.08 ≈ 70.4 kg
  • Hamwi: 48.0 + 2.7 × 10.08 ≈ 75.2 kg
  • Average: ≈ 72.5 kg (≈ 160 lb)
  • Healthy BMI range: 58.6 kg to 78.9 kg (129–174 lb)

The four formulas produce answers within a 5 kg window; the BMI range is wider still. Anywhere in that window is "a sensible weight for this height", and the right place within the window depends on body composition, training, and personal preference.

How to interpret the numbers

If you are already inside the healthy BMI range, you are in a reasonable zone by every formal definition. Use the IBW numbers as loose guidance, not as a prescription. If you are well above the range, moving toward it by even 5–10% of current body weight produces large improvements in blood pressure, blood sugar, and joint load — you do not need to hit the middle of the IBW window to see benefits.

If the IBW numbers are well below your current weight and you feel good, that is a sign the formulas are over-conservative for you. Athletes, muscular individuals, and people with naturally large frames commonly sit well above their IBW without being unhealthy. In those cases, body fat percentage or waist circumference is a better yardstick.

Common mistakes

  • Treating IBW as a goal. It is a reference, not a destination. Health markers matter more than hitting a specific kilogram.
  • Ignoring muscle mass. Strength-trained people will exceed IBW without being overweight. Use body fat percentage instead.
  • Applying adult formulas to children. IBW formulas are derived from adult data and do not apply to anyone under 18.
  • Picking the lowest number. Chasing the minimum IBW value often pushes you below the healthy BMI band.
  • Forgetting frame size. The spread between the formulas gives you an implicit frame-size window; smaller frames sit toward the low end, larger frames toward the high end.

Historical context and limits

Ben Devine published his formula in 1974 in a pharmacy journal as a tool for dosing gentamicin, an antibiotic that distributes in lean tissue. Dr George Hamwi proposed his in 1964 for diabetes nutrition counselling. Robinson and Miller published their modifications in 1983. None of these clinicians set out to invent a weight-loss target — they wanted a reasonable estimate of "a typical healthy person this tall". Six decades later, the formulas still float around fitness blogs, often presented with more authority than the data support. Use them with appropriate scepticism.

When to consult a professional

If you are considering a significant weight change, if your current weight is well outside your healthy BMI range, if you are pregnant, under 18, over 65, or recovering from an eating disorder, talk to a doctor or registered dietitian. Personalised advice from someone who can assess your body composition, health history, and training is far more valuable than any formula.

Frequently Asked Questions

What is "ideal body weight"?
Ideal body weight (IBW) is a target weight calculated from height and sex using historical formulas originally developed for clinical drug dosing. It is not a number that guarantees health, attractiveness, or fitness — it is a rough reference point derived from population averages. Treat it as one data point alongside BMI, body fat percentage, and how you feel, not as a goal to chase.
Which formula is the most accurate?
None of them is "accurate" in an absolute sense — they are all approximations. Devine (1974) is the most widely cited, especially in clinical settings for drug dosing. Robinson (1983) and Miller (1983) were published to refine Devine for modern populations. Hamwi (1964) is the oldest and tends to read slightly higher for men. We show all four plus the average so you can see the range rather than pretending there is one correct answer.
Why were these formulas originally created?
All four were developed to help clinicians calculate drug dosages based on a reasonable reference weight, especially for drugs that distribute primarily in lean tissue. Dosing a medication based on a patient's actual weight can lead to overdose in obese patients, so physicians wanted a "typical healthy" reference weight indexed to height and sex. The formulas were never intended as fitness targets, though they have drifted into popular use.
Why do the formulas only use height and sex?
Because they were built to be simple bedside tools. Adding age, frame size, body composition, or ethnicity would have improved accuracy at the cost of usability. Modern alternatives like BMI-derived healthy weight ranges, waist-to-height ratio, or body-fat-based targets are better for individual goal-setting. The classic IBW formulas survive mainly because they are embedded in medical reference material and drug dosing protocols.
Should I eat to hit my ideal weight?
Not blindly. If your current weight is far above your IBW, moving toward it is generally reasonable — but stop when you feel good and your health markers (blood pressure, blood sugar, energy, sleep) are where you want them. If your IBW falls below a BMI of 20, you may be under-fueling by chasing it. Use IBW as a rough compass, not a destination pin.
How does IBW compare to a healthy BMI range?
The calculator shows both. The healthy BMI range (18.5–24.9) is a wider band and is derived directly from your exact height, not from a rounded "inches over 5 feet" approximation. For most adults the IBW formulas land somewhere in the lower half of the healthy BMI range. If you are already inside the BMI range, you are in a sensible zone regardless of which IBW number you prefer.
Do these formulas work for very tall or very short people?
Less well. The formulas were calibrated around people near the middle of the adult height distribution. At heights below 5 ft (152 cm) they extrapolate downward and can produce implausibly small numbers; we clamp the "inches over 5 feet" input at −12 and display a warning. At very tall heights (over 200 cm) they are also less reliable. Use BMI or body-fat-based targets instead at the extremes.
Does IBW account for muscle mass?
No. A muscular athlete will weigh more than their IBW without being overweight. This is the same limitation as BMI — neither measure distinguishes muscle from fat. If you lift weights seriously, use body fat percentage rather than IBW as your primary reference point.
What about body frame size — small, medium, large?
The Hamwi formula in particular was sometimes adjusted by frame size (±10% for small or large frames). Frame-size definitions are subjective and rarely used consistently, so we do not apply that adjustment here. The spread between the four formulas in our table gives you an implicit frame-size window: the lower value is appropriate for smaller frames, the higher one for larger frames.
Is this a substitute for medical advice?
No. This calculator is an informational tool. Weight targets should be discussed with a qualified clinician if you have a medical condition, are pregnant or breastfeeding, are under 18 or over 65, are recovering from an eating disorder, or are preparing for a competitive sport. Do not use IBW as the sole basis for a weight-loss or weight-gain plan.