Ideal Weight by Age — How Your Target Changes Over Time

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 They are historical reference points developed by researchers in the mid-to-late 20th century for specific evidence-based purposes.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.

How Ideal Weight Shifts With Age

The classic ideal weight formulas (Devine, Hamwi, Robinson) use only height and sex — they do not include age. Yet body composition changes with age in ways that matter for interpretation. Muscle mass declines gradually after age 30, bone density shifts, and the proportion of weight made up by fat rises even when scale weight stays flat. That means a single formula estimate applied at age 25 and again at age 55 will read the same number, but the body behind the number is different. The practical fix is to apply a small age adjustment on top of the formula estimate, widening the acceptable range rather than changing the formula itself.

The 25 to 30 Baseline

Most ideal weight reference tables are built around adults aged 25 to 30, the age band where lean mass typically peaks and body composition is most stable. At this baseline, the formula estimate plus the ±10 percent healthy reference range gives a clean target zone. For a 175 cm man, the Devine estimate of 70.7 kg plus ±10 percent gives roughly 64 to 78 kg. For a 165 cm woman, the Devine estimate of 57 kg plus ±10 percent gives roughly 51 to 63 kg. Use this baseline range as the anchor, then apply age adjustments as described below.

Age Adjustment: 1 to 2 kg per Decade

A common practical adjustment is to allow roughly 1 to 2 kg of additional acceptable weight per decade above age 30, reflecting the natural shift in body composition that accompanies aging. The table below shows how the acceptable range widens with age for a 175 cm man (Devine baseline 70.7 kg):

The same pattern applies to women, with the baseline range adjusted for the female formula estimate. The age adjustment is descriptive, not rigid — it reflects what is typical and acceptable, not what is optimal. Many active adults who strength train maintain weight closer to the baseline range well into their 60s and 70s.

Why Older Adults Benefit From Slightly Higher Weight

For adults aged 65 and older, a slightly higher weight within or just above the reference range is often associated with better long-term outcomes than the lower end of the range. The reasons are practical. Extra reserve supports resilience during periods of stress, unintentional weight loss, or recovery, all of which become more common with age. Sarcopenia — the gradual loss of skeletal muscle — means older adults may sit at a lower scale weight while carrying proportionally more fat, so a slightly higher total weight often reflects preserved muscle. Low body weight in older age is associated with weaker grip strength, slower recovery, and reduced mobility. For older adults, strength, mobility, and energy often matter more than hitting a specific number on the scale.

Muscle Preservation Shifts the Trend

The age-related rise in acceptable weight assumes the typical pattern of muscle loss. Adults who resistance train two to three times per week and eat adequate protein (roughly 1.2 to 1.6 g per kg of body weight for older adults) slow that muscle loss substantially. Many active adults in their 50s and 60s maintain weight and body composition closer to the 25 to 30 baseline than the age-adjusted range. This is the strongest argument for resistance training across the lifespan: it preserves the muscle that keeps body composition favorable and lets you stay near the baseline range rather than drifting upward. The age adjustment is a safety margin for typical aging, not a license to let weight climb without attention.

Practical Tips by Age

• In your 20s and 30s, anchor to the formula estimate plus ±10 percent. Build the strength and muscle reserve you draw on for decades.
• In your 40s and 50s, allow 1 to 4 kg above the baseline range, but prioritize resistance training and protein to slow muscle loss.
• In your 60s and beyond, favor the upper half of the range. Strength, mobility, and energy matter more than the lowest possible weight.
• Pair ideal weight with body fat percentage and waist circumference. Composition matters more than scale weight, especially with age.
• Re-evaluate annually. The formula estimate itself is stable, but your acceptable range widens with age.