Ideal Weight Calculator

What Is an Ideal Weight Calculator?

An ideal weight calculator estimates a reference body weight from height and sex. Instead of presenting one number as a universal target, this calculator compares four commonly used ideal body weight (IBW) formulas: Devine, Robinson, Miller, and Hamwi.

It also shows a BMI-based healthy weight range. This gives you two different reference points: traditional IBW equations provide formula-based estimates, while BMI provides a range of body weights corresponding to an adult BMI of 18.5–24.9.

These approaches are not interchangeable, and neither should be treated as a precise definition of the weight every person should reach. Research and clinical reviews have highlighted important limitations in traditional IBW equations.

How Is Ideal Body Weight Calculated?

The four formulas used here are traditional height-based equations. Most use a base weight at 5 feet and add a fixed amount for each inch above 5 feet. The equations produce different estimates because they were developed from different historical data and approaches.

Devine Formula (1974)

The Devine formula was published in 1974 and became widely used for ideal body weight estimation in clinical and drug-dosing contexts. It is the most commonly cited IBW equation in clinical pharmacology.

• Men: 50.0 kg + 2.3 kg × each inch over 5 ft
• Women: 45.5 kg + 2.3 kg × each inch over 5 ft

Worked example (men, 5'10"): 50 + 2.3 × 10 = 73 kg (≈ 161 lb).

Best for: Clinical drug-dosing and pharmacokinetic calculations. It remains the standard reference in many medical contexts.

Limitation: Because it was developed for drug dosing, it was not designed to identify healthy body-composition targets for athletes or the general population.

Hamwi Formula (1964)

The Hamwi method is traditionally expressed in pounds. This calculator calculates it in its common imperial form and converts the result to kilograms when metric output is selected.

• Men: 106 lb + 6 lb × each inch over 5 ft
• Women: 100 lb + 5 lb × each inch over 5 ft

Worked example (men, 5'10"): 106 + 6 × 10 = 166 lb (≈ 75.3 kg).

Best for: A widely recognized imperial reference. Sometimes used alongside Devine in clinical settings.

Limitation: Hamwi often produces different estimates than Devine, and the direction and size of the difference varies with height and sex. It was developed before modern body-composition standards.

Robinson Formula (1983)

The Robinson equation was published in 1983 using height-weight data derived from Metropolitan Life Insurance Company tables.

• Men: 52.0 kg + 1.9 kg × each inch over 5 ft
• Women: 49.0 kg + 1.7 kg × each inch over 5 ft

Worked example (men, 5'10"): 52 + 1.9 × 10 = 71 kg (≈ 156.5 lb).

Best for: A moderate estimate between Devine and Miller. Sometimes preferred when a slightly lower reference value is appropriate.

Limitation: Also derived from historical insurance data that may not reflect modern body compositions.

Miller Formula (1983)

The Miller equation is another 1983 reference equation with different coefficients from Devine, Hamwi, and Robinson.

• Men: 56.2 kg + 1.41 kg × each inch over 5 ft
• Women: 53.1 kg + 1.36 kg × each inch over 5 ft

Worked example (men, 5'10"): 56.2 + 1.41 × 10 = 70.3 kg (≈ 155 lb).

Best for: A reference estimate that tends to produce lower values than Devine or Hamwi for the same height.

Limitation: Least commonly used in clinical settings. Same historical data limitations as the other formulas.

Below 5 Feet: Extrapolated Estimates

Traditional IBW equations use 5 feet (152 cm) as their baseline and add a fixed amount for each additional inch. For heights below 5 feet, the calculation extrapolates below this baseline. The extrapolated values are reference estimates rather than results validated in the original clinical datasets.

If your height is below 5 feet, treat the formula results with additional caution. A BMI-based range may provide a more useful secondary reference in this height range.

Which Ideal Body Weight Formula Is Most Accurate?

There is no universally accepted "most accurate" IBW formula. Devine, Hamwi, Robinson, and Miller can produce different results for the same height because they were developed from different historical datasets and methods.

Research comparing traditional IBW equations with BMI-based ranges has found that the formulas do not always align with the same BMI value across different heights. This is one reason a BMI-based range can provide useful additional context rather than relying on one formula alone.

RepMaths therefore shows the four equations separately and reports their overall range. The calculator does not rank one formula as the universally correct answer.

What Should I Weigh for My Height and Age?

For the adult IBW formulas on this page, age is not part of the calculation. Devine, Hamwi, Robinson, and Miller use height and sex rather than age.

So a search such as "ideal weight by age" should not be interpreted as though every adult age has a separate IBW number from these equations. Age can matter when assessing health, body composition, or other individual factors, but it is not an input to these four classic IBW formulas.

For adults, you can use the BMI Calculator alongside this tool to see how weight relates to height using a BMI-based reference range.

Ideal Weight vs Healthy Weight

"Ideal weight" and "healthy weight" are not interchangeable terms. Traditional IBW formulas return mathematical reference estimates, while a broader healthy-weight assessment can involve BMI, body composition, health history, physical activity, and other individual factors.

A person can be above a traditional IBW estimate without having excess body fat, particularly when they have substantial muscle mass. Conversely, being within an IBW estimate does not automatically mean that a person has an optimal body composition or overall health.

Does Ideal Weight Include Muscle Mass?

No. Traditional IBW equations do not directly measure muscle mass, fat mass, skeletal size, or fat distribution. They primarily use height and sex.

This limitation matters for bodybuilders, strength athletes, and muscular lifters. Someone who carries substantially more lean mass than the population represented by a traditional height-weight equation may weigh more than the calculated IBW while still having a healthy body composition.

If you are a lifter, use the result as a reference rather than as a mandatory target. Our Body Fat Calculator can provide additional body-composition context.

You can also use the Lean Body Mass Calculator to estimate fat-free mass, or the FFMI Calculator to put lean mass into a height-adjusted context.

Ideal Weight for Bodybuilders and Lifters

If you lift weights regularly, an IBW calculator can produce a result that feels surprisingly low. That does not necessarily mean that you should lose weight to reach the calculated number.

Traditional IBW equations were not designed to identify the ideal scale weight for a muscular athlete. They also do not distinguish how much of your body weight comes from muscle versus fat.

For a fitness-focused assessment, consider your body-fat percentage, lean body mass, performance, health markers, and personal goals alongside scale weight.

If your goal is to move toward a specific body weight, the Calorie Deficit Calculator can help estimate a calorie target and projected timeline.

If your goal is nutrition planning rather than weight loss, the Macro Calculator can help you set starting protein, carbohydrate, and fat targets.

What Is the Healthy BMI Weight Range?

For adults, a BMI of 18.5 through 24.9 is commonly used as the healthy-weight BMI category. Converting those BMI values back into body weight creates a height-specific reference range.

The calculation is: Weight = BMI × Height² when height is expressed in meters and weight in kilograms.

Unlike traditional IBW formulas, a BMI range gives you more than one target weight. However, BMI is a screening measure and cannot distinguish muscle mass from fat mass.

For that reason, muscular athletes should not interpret BMI or traditional IBW as a complete body-composition assessment.

Why Do Different Ideal Weight Calculators Give Different Results?

Different calculators may use different equations. Some use Devine, some use Robinson or Miller, and others use Hamwi or BMI-based calculations.

Even when two calculators use the same formula, differences can appear because of rounding, height conversion, unit conversion, or how heights around the 5-foot baseline are handled.

RepMaths shows the four reference equations separately so you can see the calculation rather than hiding those differences behind one unexplained number.

Frequently Asked Questions

Sources & Methodology

RepMaths uses four commonly published adult ideal body weight reference equations: Devine, Hamwi, Robinson, and Miller. It also calculates a separate BMI-based weight range using BMI values of 18.5 and 24.9.

• Devine BJ. Gentamicin therapy. Drug Intelligence and Clinical Pharmacy, 1974.
• Robinson JD, Lupkiewicz SM, Palenik L, Lopez LM, Ariet M. Determination of ideal body weight for drug dosage calculations. American Journal of Hospital Pharmacy, 1983.
• Pai MP, Paloucek FP. The origin of the "ideal" body weight equations. Annals of Pharmacotherapy, 2000.
• Peterson CM, Thomas DM, Blackburn GL, Heymsfield SB. Universal equation for estimating ideal body weight and body weight at any given body mass index. PLoS ONE, 2016.

The formulas are presented as reference estimates for educational and fitness-planning purposes. They are not a diagnosis and should not be treated as a universal target or a substitute for individualized medical advice.