Ideal Weight Calculator

Understanding the Ideal Weight Calculator

An ideal weight calculator applies the Devine formula alongside a healthy BMI range. It's worth knowing at the outset that the Devine formula was never designed as a health target: it was created in 1974 for calculating medication doses, and its use as a body-image benchmark is a repurposing its author never intended.

How it actually works

Enter your height and the calculator applies the Devine formula, which starts from a base weight at 5 feet and adds 2.3 kilograms per additional inch, showing separate male and female figures. It also converts the healthy BMI range of 18.5 to 24.9 into a weight range for your height. At 5 feet 8 inches, Devine gives about 150.8 pounds for men and 140.9 for women.

The deeper context most people miss

Notice that Devine produces a single number while the BMI approach produces a range spanning 40 pounds or more. That difference is meaningful: there is no single correct weight for a given height, and the range reflects genuine variation in frame size, muscle mass, and body composition. Treating the single Devine figure as a target mistakes a drug dosing convenience for a health goal.

Where these formulas came from and what they were built for

The Devine formula was published by Dr B J Devine in 1974 in the context of calculating doses of certain medications, particularly aminoglycoside antibiotics, where dosing based on actual body weight in patients with obesity risks toxicity because the drug distributes primarily into lean tissue. Devine needed a standardised estimate of lean body size derived from height, and by his own account the formula was arrived at somewhat arbitrarily rather than derived from population data on healthy weight. It has remained genuinely useful for its intended purpose and continues to appear in clinical pharmacology. Similar formulas followed, including Robinson and Miller in 1983 and Hamwi somewhat earlier, each producing slightly different numbers from the same reasoning. None of them was developed as a health or aesthetic target. The distinction matters because a formula validated for estimating lean mass for drug distribution has no particular claim to describing the weight at which a given person is healthiest. Population health evidence points in a different direction: the relationship between body weight and health outcomes is a broad range rather than a point, it varies with age, sex, ethnicity, and body composition, and the weight associated with lowest mortality in large cohort studies frequently sits somewhat higher than these formulas suggest, particularly at older ages. Presenting a single number as an ideal implies a precision the underlying science does not support.

A worked example: the same height, several legitimate weights

At 5 feet 8 inches, Devine suggests 150.8 pounds for a man, while the healthy BMI range spans 122 to 164 pounds. Consider three men at that height. The first weighs 145 pounds with modest muscle mass and a sedentary lifestyle; he sits below the Devine figure and within the BMI range. The second weighs 175 pounds after years of resistance training, with a waist measurement of 32 inches and a body fat percentage around 14%; he exceeds both the Devine number and the BMI range and is by any meaningful measure in excellent condition. The third weighs 150 pounds, matching Devine almost exactly, but carries most of it around the abdomen with a 38-inch waist and little muscle, a pattern sometimes described as normal weight obesity, and his metabolic risk markers may be worse than the second man's. The formula ranks these three in an order that has little to do with their actual health. This is the central problem with weight-based targets generally, and it's why clinical practice increasingly pairs weight with waist circumference, body composition where available, and metabolic markers including blood pressure, glucose, and lipids, none of which correlate reliably with hitting a formula-derived number.

Deciding whether a weight target is the right goal at all

For many people, a specific weight target is less useful than the outcomes they actually care about, and reframing tends to produce better results. If the underlying goal is health, the measures with strong evidence are cardiovascular fitness, strength, waist circumference, blood pressure, glucose regulation, and lipid profile, all of which can improve substantially without large weight change, and improvements in fitness in particular are associated with reduced mortality risk somewhat independently of weight. If the goal is athletic performance, the relevant target is body composition and power-to-weight ratio for the specific sport rather than a general formula. If the goal is appearance, that's a legitimate personal preference, though it's worth recognising that a formula from a 1974 pharmacology paper is an arbitrary anchor for it. There's also a practical argument for range-based rather than point targets: body weight fluctuates by several pounds day to day from fluid, food volume, glycogen, and hormonal cycles, so a single-number target guarantees frequent apparent failure regardless of actual progress. Setting a range, tracking a weekly average rather than daily readings, and pairing weight with a measurement like waist circumference gives a far more stable and informative picture. If weight has become a source of significant distress, or if pursuing a target is affecting eating patterns, that's worth discussing with a doctor or registered dietitian rather than working through with a calculator.

Why formula-based ideal weight is particularly poor for some groups

The limitations fall unevenly. Athletes and anyone with substantial muscle mass are systematically misclassified, since these formulas estimate a standardised lean size from height alone and have no way to account for genuinely higher muscle. Older adults are another group where the standard advice misleads: evidence increasingly suggests that a somewhat higher body weight is associated with better outcomes in later life, possibly reflecting the protective value of reserves during illness and the greater danger of sarcopenia and frailty than of moderate excess weight. Formulas derived largely from populations of European descent may fit other populations poorly, and the recognition that health risk begins at different body sizes across ethnic groups has led several countries to adopt different BMI thresholds. Very tall and very short people are poorly served, since the linear addition of 2.3 kilograms per inch is an approximation that breaks down at the extremes. People with limb differences, amputations, or significant fluid retention fall outside the formulas' assumptions entirely, and clinical adjustments exist for exactly this reason in the drug dosing context where the formula is genuinely used. Pregnancy makes the concept inapplicable. Children and adolescents require growth charts and percentiles rather than adult formulas of any kind. Given how many groups the caveats cover, the honest position is that formula-derived ideal weight is a rough population reference with narrow legitimate use.

Variations: Robinson, Miller, Hamwi, and BMI-based ranges

Several formulas exist and produce different numbers from the same height, which is itself informative about their precision. Hamwi, from the 1960s, uses 106 pounds at 5 feet plus 6 pounds per inch for men, and 100 pounds plus 5 pounds per inch for women. Robinson from 1983 uses 52 kilograms plus 1.9 per inch for men. Miller, also 1983, uses 56.2 kilograms plus 1.41 per inch. At 5 feet 8 inches these span roughly 10 pounds, and there's no principled basis for preferring one. BMI-based ranges are generally more defensible for health purposes because they derive from population outcome data rather than from clinical convenience, though BMI carries its own well-known limitations around body composition. Adjusted body weight, used in clinical settings, adds a fraction of the excess over ideal weight for patients with obesity, which matters for drug dosing. For body composition rather than weight, methods including waist-to-height ratio, body fat percentage estimation, and DEXA scanning provide information that no height-based formula can.

Using this calculation appropriately

Recognise that the Devine formula was designed in 1974 for medication dosing rather than as a health target, and that its use as a body-image benchmark is a repurposing without scientific backing. Prefer the BMI-derived range over the single Devine figure, since the range reflects genuine variation in frame size and body composition and derives from population outcome data. Pair any weight figure with waist circumference, which captures abdominal fat that weight alone cannot, using the guideline of keeping waist below half your height. Consider whether a weight target is the right goal at all, since fitness, strength, blood pressure, and glucose regulation can improve substantially without large weight change and carry strong independent evidence. Track a weekly average rather than daily readings if you do use weight, since day-to-day fluctuation of several pounds is normal. And speak to a doctor or dietitian if weight has become a source of distress.

What people get wrong

• Treating the Devine figure as a health target, when it was created in 1974 for medication dosing and was, by its author's account, arrived at somewhat arbitrarily.
• Reading a single number as the correct weight, when the healthy BMI range for the same height spans 40 pounds or more and reflects genuine variation.
• Applying these formulas to athletes or anyone with substantial muscle, who are systematically misclassified since height-based formulas cannot see body composition.
• Using an adult formula for older adults without adjustment, when evidence suggests somewhat higher weight is associated with better outcomes in later life.

Where the math comes from

Devine formula: 50 kg + 2.3 kg per inch over 5 feet for males, and 45.5 kg + 2.3 kg per inch over 5 feet for females. The healthy weight range is derived from BMI, calculated as BMI × height in metres squared, using the standard range of 18.5 to 24.9. The Devine formula was developed for estimating lean body size in medication dosing rather than as a health or aesthetic target.

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