Ideal Weight in kg — Metric Body Weight Calculator

What an Ideal Weight Formula Tells You

An ideal weight formula is a simple height-based equation that estimates a typical body weight associated with general wellness in large population samples. The word "ideal" is misleading — these formulas were never intended to give a single perfect number for each individual. They are historical reference points developed by researchers in the mid-to-late 20th century for specific evidence-based purposes. Think of them as three rough estimates from three different eras, not as personal targets written in stone.

Our calculator displays three formulas side by side: Devine (1974), Hamwi (1964), and Robinson (1983). Each was derived on a different population using different statistical approaches, which is why they disagree by several kilograms for the same height. Presenting all three together lets you see the plausible range of reference weights rather than pretending any one formula is uniquely correct. We also show a ±10 percent band around each estimate because human healthy weight naturally spans a meaningful range even at identical height and sex.

The Three Formulas

All three formulas use the same underlying structure: a baseline weight at 5 feet (152.4 cm) plus an additional weight per inch of height above 5 feet. The constants vary. For heights below 5 feet, the math works out to subtractions rather than additions, and in practice the formulas become increasingly unreliable the further below 5 feet you go.

Devine Formula — Primary. Where It Came From and Why It Matters

The Devine formula is the most commonly referenced ideal weight equation in modern medical literature and evidence-based practice, but it was never actually designed to tell anyone what they should weigh. Dr. B. J. Devine published his famous constants in 1974 for a very specific purpose: estimating lean body weight in adult men and women so that clinicians could calculate appropriate compounds proper amounts, most notably for the anticoagulant heparin and certain chemotherapeutic agents whose safe dosing window depends on the volume of distribution of lean tissue rather than total body weight.

Devine himself did not call the result an "ideal weight." He derived his constants from a small set of earlier studies that had measured lean body mass via isotope dilution in a limited sample of adults. Over time, clinicians and textbooks began to use Devine's lean body weight estimate as a convenient shorthand for a "reasonable weight" in conversation with adults, and from there it spread into online calculators and popular wellness writing. Today the Devine formula is the default primary estimate in this calculator precisely because it is the most-cited historical reference in peer-reviewed literature, not because anyone in 2025 believes it is a definitive ideal target.

The Devine formula has no frame-size adjustment. This is an important limitation. Two adults with identical height and sex but very different skeletal frame sizes will receive the same Devine estimate even though the larger-framed person can healthily carry several kilograms more than the smaller-framed person. Our UI presents a frame-size selector so you can mentally contextualize the results: if you know you have a broad, large build, the upper end of the ±10 percent band is a more appropriate reference than the midpoint. For small-framed individuals, the lower end of the band is typically a better personal reference.

Hamwi and Robinson — Historical Context

The Hamwi formula was developed in 1964 and was widely used in evidence-based nutrition through the 1970s and 1980s. It produces slightly higher estimates for men and slightly lower estimates for shorter women compared to Devine. It was the standard "ideal weight" taught in many nutrition schools for a generation and still appears in some older dietary software and insurance tables. The Hamwi formula is also the basis for the Broca index variants you still occasionally see in older European textbooks.

The Robinson formula was published in 1983 specifically for athletic populations after researchers observed that Devine and Hamwi estimates were often unrealistically heavy for shorter athletes and unrealistically light for taller athletes. Robinson used a lower per-inch coefficient for both sexes and a heavier baseline at 5 feet. For people 5 ft 10 and taller, Robinson typically gives the lightest of the three estimates, which is why it is sometimes preferred in strength and conditioning contexts where high lean mass at a given height is common.

Worked Example

For a 175 cm (5 ft 9 in) male. 5 ft 9 in is 9 inches over 5 ft. Devine: 50.0 + 2.3 × 9 = 70.7 kg. Hamwi: 48.0 + 2.7 × 9 = 72.3 kg. Robinson: 51.7 + 1.86 × 9 ≈ 68.4 kg. The three formulas span a range of roughly 4 kg for this example, which is entirely typical and illustrates why no single formula should be addressed as a definitive answer. Taking each result and applying a ±10 percent healthful band gives a wide but realistic reference window.

FAQ-Style Explanations

Why doesn't the calculator adjust Devine for frame size? The original Devine formula has no frame-size term. Adding one would make it no longer the Devine formula. Some textbooks and calculators do add ±10 percent adjustments for small, medium, and large frame, but these adjustments were not part of the original publication and are not standardized across sources. To keep the formulas historically faithful, we display the unmodified Devine number as the primary result and present the ±10 percent band beneath it as a general healthy range that naturally accounts for frame.

If all three formulas disagree, which one should I use? Start with the Devine estimate as the most common medical literature reference. Then compare your current weight, how you feel, how your clothes fit, and your energy levels. If you feel energetic, recover well, have regular menstrual cycles if applicable, sleep well, and have normal blood markers at a weight outside these formulas, that weight is fine for you. These are population references, not verdicts.

How does frame size affect healthy weight? Skeletal frame size — measured roughly by wrist circumference, elbow breadth, or shoulder width relative to height — creates a range of healthy weights that can differ by 8 to 12 kg between a small-framed and large-framed person of the same height and sex. Frame size has a genetic component and does not change in adulthood. People who are large-boned are not "overweight" simply because they exceed a formula midpoint. Use the ±10 percent band and your own common sense.

Known Limitations

• These formulas were never designed as standalone wellness tools. Devine was for compounds dosing, Hamwi was for older evidence-based practice, Robinson was for athletic populations.
• None of them account for body composition. Two people with identical height and sex can have the same weight but very different ratios of muscle to fat with very different metabolic health profiles.
• None of them account for age. Body composition changes with age, and a weight that is appropriate at 30 may or may not be appropriate at 70.
• Reliability degrades at heights far from the 5 ft baseline. The formulas become increasingly speculative for people shorter than roughly 150 cm or taller than roughly 195 cm.
• No prospective study has ever shown that matching one of these formula midpoints produces better long-term health outcomes than simply staying within a broad BMI Normal band and maintaining consistent physical activity and good nutrition.
• Not intended for use by children, adolescents, or pregnant or lactating individuals.

Ideal Weight in Metric Units

The classic ideal weight formulas were originally published in metric units — kilograms for weight and centimeters for height — which makes the kg version the native form of the Devine, Hamwi, and Robinson equations. Working in metric avoids the rounding that comes from converting feet and inches, and it lines up with how most of the world measures body weight. The Devine formula gives men 50 kg plus 2.3 kg per inch over 5 feet (152.4 cm), and women 45.5 kg plus 2.3 kg per inch over 5 feet. Because the per-inch increment is in kg, the metric output is direct, with no further conversion needed.

The Devine Formula in kg

The term (height in cm − 152.4) ÷ 2.54 converts the height above 5 feet into inches, since 2.54 cm equals 1 inch. For a 178 cm man: (178 − 152.4) ÷ 2.54 = 10.08 inches over 5 feet, so Devine gives 50 + 2.3 × 10.08 = 73.2 kg. For a 165 cm woman: (165 − 152.4) ÷ 2.54 = 4.96 inches over 5 feet, so Devine gives 45.5 + 2.3 × 4.96 = 56.9 kg. Apply the ±10 percent healthy reference range to widen the target zone for frame size and muscle mass.

Height (cm) to Weight (kg) Reference Table

Metric and Imperial Conversion

If you need to move between metric and imperial units, the conversions are simple. For weight, 1 kilogram equals 2.2046 pounds, so multiply kg by 2.2046 to get lb, or divide lb by 2.2046 to get kg. For height, 1 inch equals 2.54 cm exactly, so multiply inches by 2.54 to get cm, or divide cm by 2.54 to get inches. To convert feet and inches to cm, first convert to total inches (feet × 12 + inches) then multiply by 2.54. A 5'9" person is 69 inches, or 175.3 cm. A 70 kg person weighs 154.3 lb. Most calculators handle these conversions automatically, but knowing the factors helps you sanity-check the results.

Cross-Check With BMI in kg

The BMI Normal band (18.5 to 24.9) gives an independent weight range in kg for any height in cm. The BMI formula in metric units is weight in kg divided by height in meters squared. For a 175 cm (1.75 m) person, BMI 18.5 corresponds to 18.5 × 1.75² = 56.6 kg, and BMI 24.9 corresponds to 24.9 × 1.75² = 76.2 kg. The Devine estimate of 70.7 kg sits inside this band. The two methods usually agree for medium-frame adults with average muscle mass. Where they disagree is informative: if your formula estimate sits well outside the BMI band, double-check your height input; if your actual weight sits outside both, that signals a meaningful gap to address through training and nutrition.

Practical Tips

• Use the metric table directly if you measure your height in cm and weight in kg. No conversion needed.
• Apply the ±10 percent healthy reference range to widen the target zone for your frame size and muscle mass.
• Cross-check the formula estimate against the BMI 18.5 to 24.9 kg range for your height. The two should agree for medium-frame adults.
• If you switch between metric and imperial, use 2.2046 for kg-to-lb and 2.54 for cm-to-inch to avoid rounding drift.
• Pair the kg target with body fat percentage and waist circumference for a fuller picture of body composition.