Ideal Weight Calculator

"What should my ideal weight be?" is the opening question of almost every patient walking into a nutrition clinic. In my clinical experience, I observe that focusing on a healthy weight range rather than a single number yields the most sustainable results. The answer is not simple, because ideal weight is not a single number but a range, and few people know the formulas behind it. This ideal weight calculator applies the six most widely used formulas (Hamwi, Devine, Robinson, Miller, Lorentz, BMI 22) at the same time, presents their average, and — if you choose — refines the calculation with your wrist circumference and activity level.

This updated assessment also shows your lean body mass (LBM), body surface area (BSA), and a sustainable goal plan (how many weeks + target date) to reach your ideal weight from your current weight. For users over 65, a protective-weight note appears automatically, and for the Asian/Turkish population, an alternative threshold notice is available. Now let's unpack the science behind the number.

What Is Ideal Weight? The "No Single Number" Approach

Ideal weight is the weight range at which all body functions (heart, metabolism, hormones, immunity) operate most efficiently when height, age, gender, and body frame are evaluated together. It is not aesthetic; clinically it is tied to the longest life expectancy and lowest chronic-disease risk.

👩‍⚕️ DIETITIAN'S NOTE: The calculator says "you should be 62 kg," but in the real world you can be perfectly healthy at ±5% around this number (roughly 59-65 kg). If you have high muscle mass or a large frame, being closer to the upper limit is normal; with a small frame, being closer to the lower limit is normal.

6 Different Formulas — Which Is Right? (Hamwi → Lorentz Comparison)

In the result panel you will see six different formula results side by side. Which one is "right" is less clear than people assume; each formula has merits tied to its era and the population on which it was developed.

• Hamwi (1964): The oldest clinical formula. Used for decades in drug-dose calculations; now superseded by Devine but historically important.
• Devine (1974): Still the standard for drug-dose calculation. Used routinely across all health systems; the safe dose of intravenous drugs is calculated against the Devine ideal weight.
• Robinson (1983): A more realistic revision of Hamwi and Devine. Frequently preferred in general nutrition guidelines.
• Miller (1983): The formula producing the lowest results. Sets a more aggressive boundary for individual goal-setting.
• Lorentz (age-adjusted): The only formula that incorporates an age factor. Adds a small buffer for every year above 20 — the math of the sarcopenia-protective approach.
• BMI 22 (Lemmens, 2005): Uses BMI 22 (the midpoint of the healthy range) as the target. In large population studies, the lowest mortality risk is observed at this BMI.

Our tool shows the arithmetic mean of these six formulas as the "recommended ideal weight." Using multiple perspectives instead of a single formula improves the precision of the estimate.

Determine Your Body Frame With Wrist Circumference

Two people can be the same height but one may be "small-framed" (delicate skeleton) and another "large-framed" (broad shoulders, thicker bones). This difference directly affects ideal weight: a small-framed individual's ideal can be 6-10 kg lower than a large-framed individual's.

The most practical measurement method is the Grant formula: we measure the thinnest part of your wrist with a tape and compute the height/wrist ratio. Thresholds:

If you enter the measurement in the tool's optional "Wrist Circumference" field, your frame is detected automatically and a -10% for small, 0 for medium, +10% for large correction is applied to the ideal weight. A "large-frame-adjusted" or "small-frame-adjusted" note appears in the result card.

Lean Body Mass (LBM) and Body Surface Area (BSA): Clinical Metrics

Ideal weight answers the "how much" question; LBM answers the "how much of the weight is NOT fat" question. Lean Body Mass (LBM) is the sum of bone, muscle, organs, and fluid. The Boer formula we prefer:

• Male: LBM = (0.407 × weight_kg) + (0.267 × height_cm) − 19.2
• Female: LBM = (0.252 × weight_kg) + (0.473 × height_cm) − 48.3

LBM is a natural alternative to BMI, which cannot distinguish muscle from fat in athletes. Your LBM value is shown automatically in the result card.

Body Surface Area (BSA) is used in medicine for drug dosing, cardiac output, and metabolic rate calculations. The Du Bois formula has been the standard since 1916:

• BSA (m²) = 0.007184 × weight_kg^0.425 × height_cm^0.725

A healthy adult typically has a BSA between 1.5-2.0 m². This metric determines chemotherapy doses in oncology and the cardiac index in cardiology. Your BSA value also appears in a small card in the result panel.

Ideal Weight Changes With Age: 30/40/50/60+ Tables

As age advances, metabolism slows, muscle mass declines, and body composition changes. For this reason, age-flexible ideal ranges have been developed. The table below is a reference; an individual target may shift ±2-3 kg around it.

If you enter an age of 65 or above in the "Age" field, a "Protective Weight" note is displayed automatically in the result card. The Lorentz formula already incorporates age adjustment; the average of the six formulas reflects this correction.

How Long Should It Take to Reach Ideal Weight? Goal Plan

A comprehensive assessment does not just state "your ideal weight is X"; it also shows how many weeks and on which date you can reach the ideal from your current weight. The sustainability targets are evidence-based:

• Weight loss: 0.5 kg per week (2 kg per month, about 1-2% of current weight). Faster weight loss raises the risk of muscle loss, metabolic adaptation (slowdown), and rebound.
• Weight gain: 0.3 kg per week (1.2 kg per month). Faster gain becomes fat-dominant; the right pace yields muscle-dominant gain.

The "Goal Plan" box in the result card uses this pace to auto-compute the number of weeks and the target date. For example, someone who needs to lose 8 kg reaches the ideal in 16 weeks (~4 months). If you are already in the ideal range (difference between current and ideal <1.5 kg), the plan box shows a "Congratulations" message.

Women-Men Differences + Athlete Exception

The BMI formula is gender-independent, but ideal-weight formulas (Hamwi, Devine, Robinson, Miller) use different coefficients by gender. The base weight and incremental factors for men are higher; the physiological reason is that men have higher natural muscle-bone density than women.

A critical exception applies to athletes: professional athletes (body fat <10% in men, <18% in women) may appear 5-10% above ideal weight — that excess comes from muscle mass, not fat. If you select "Active" or "Very Active" in the tool's activity field, an extra note appears in the result card. For a deeper muscle-fat distinction, you can also use our body fat percentage calculation.

65+ Older Adults and the Asian Population: Threshold Notes

The standard ideal-weight formulas were developed on a Caucasian adult population. Two important special cases exist:

• 65+ older adults: To protect against sarcopenia (age-related muscle loss), the BMI target range is widened to 23-29.9. Excessively low weight in this age group raises frailty, fall, and infection risk. The geriatric nutrition approach page covers this in detail.
• Asian/Turkish population: The WHO Asia-Pacific guideline lowers the cardiometabolic risk threshold to BMI 23. Using BMI 22 as the ideal-weight anchor yields a safer range. Because the Turkish population reflects a Mediterranean-Asian phenotype mix, both thresholds (BMI 22 and classic BMI 22.5) should be considered. This notice appears as a collapsible info box in the result card. For a broader framework, you can review the Asian threshold section in our BMI calculation thresholds.

Warning for Children + Roadmap

These formulas and metrics are strictly for adults (age 18+). Because growth hormones are active in children and adolescents, adult formulas are misleading. If you enter an age under 18 in the tool, an automatic warning box is displayed.

For children, age- and sex-specific percentile curves (growth tracking) are used. When a family has weight concerns about a child, instead of applying adult diets they should consult a pediatric nutrition specialist.

Let's Draw the Right Roadmap for You

Ideal weight is a starting point; the real success is how — and over what timeframe — you get there. The recommended ideal weight, healthy range, and goal plan the tool provides form the skeleton of a personalized nutrition program but are not enough on their own. Your metabolic rate, hormonal status, lifestyle, and current chronic conditions are what actually draw the roadmap.

You can contact me using the form below or via the online diet counseling page. Take the right step today to reach the ideal weight the calculator suggests with an evidence-based, sustainable method.

Related Scientific Resources

• National Institutes of Health (NIH) — Healthy Weight
• World Health Organization (WHO) — Obesity and Overweight Fact Sheet
• Centers for Disease Control and Prevention (CDC) — Assessing Your Weight
• American Heart Association (AHA) — Losing Weight
• Mayo Clinic — Metabolism and Weight Loss