Weight Calculator

What This Tool Does

This calculator estimates your ideal body weight (IBW) based on your height, age, and gender. It runs your inputs through four widely referenced formulas simultaneously and also shows the healthy weight range based on WHO BMI guidelines — so you can see how the results compare side by side. It is useful as a general reference point, not a prescription for a specific target weight.

You can also use this PPP Calculator.

How It’s Calculated

All four IBW formulas share the same structure: a base weight for a height of 5 feet, with a fixed amount added per inch above that. They differ in the exact values used, reflecting different research approaches and target populations.

The Four Formulas

Hamwi Formula (1964)

• Male: 48.0 kg + 2.7 kg per inch over 5 feet
• Female: 45.5 kg + 2.2 kg per inch over 5 feet

Devine Formula (1974) — most widely used

• Male: 50.0 kg + 2.3 kg per inch over 5 feet
• Female: 45.5 kg + 2.3 kg per inch over 5 feet

Robinson Formula (1983)

• Male: 52 kg + 1.9 kg per inch over 5 feet
• Female: 49 kg + 1.7 kg per inch over 5 feet

Miller Formula (1983)

• Male: 56.2 kg + 1.41 kg per inch over 5 feet
• Female: 53.1 kg + 1.36 kg per inch over 5 feet

Worked Example — Male, 5’10” (178 cm):

• Hamwi: 48.0 + (2.7 × 10) = 75.0 kg
• Devine: 50.0 + (2.3 × 10) = 73.0 kg
• Robinson: 52 + (1.9 × 10) = 71.0 kg
• Miller: 56.2 + (1.41 × 10) = 70.3 kg

The spread across formulas — about 5 kg in this example — is normal. No single formula is definitively correct, which is why comparing all four gives a more useful range than picking one number.

Healthy BMI Range

The WHO defines a healthy BMI as 18.5 to 25.0 for adults. The corresponding healthy weight range for any height is:

• Lower bound: 18.5 × height² (in metres)
• Upper bound: 25.0 × height² (in metres)

For a height of 178 cm (1.78 m):

• Lower: 18.5 × (1.78)² = 58.6 kg
• Upper: 25.0 × (1.78)² = 79.2 kg

This gives a wider range than the IBW formulas, reflecting that a healthy weight is a range, not a single number.

Factors That Affect Ideal Weight

Height: The primary driver in all IBW formulas. Taller individuals have proportionally more muscle mass and bone, which contributes to higher healthy weight ranges.

Gender: Men generally weigh more than women at the same height due to higher average muscle mass and bone density. The formulas account for this with different base values and increments by sex.

Age: IBW formulas are designed for adults and are most applicable from late adolescence onward. As people age, lean muscle mass naturally decreases and body fat tends to increase even if total weight stays the same. The formulas do not adjust for this shift in body composition with age.

Body frame size: People with larger bone structures naturally weigh more at the same height. Frame size can be estimated using wrist circumference relative to height — large-framed individuals may comfortably sit above IBW formula outputs without this being a health concern.

Muscle mass: IBW formulas do not distinguish between muscle and fat. A highly trained athlete may weigh significantly above their formula-derived IBW while carrying very little body fat — and be in excellent health. Conversely, someone at their “ideal” weight may still have an unhealthy body composition if muscle mass is low and fat mass is high.

Edge Cases and Special Rules

Children and teenagers: All four IBW formulas are calibrated for adults aged 18 and above. For children and adolescents, the CDC recommends using BMI-for-age percentile charts, which account for the fact that healthy weight ranges shift significantly during growth. A BMI between the 5th and 85th percentile is considered healthy for children aged 2–20.

People at height extremes: The formulas become less reliable at very short or very tall heights, where the linear weight-per-inch increment does not accurately reflect physiology. Use the BMI range as a cross-check in these cases.

Pregnancy: Weight during pregnancy increases naturally and continuously — IBW formulas are not applicable during pregnancy. Weight gain during pregnancy is guided by pre-pregnancy BMI and obstetric recommendations.

People with physical disabilities or amputations: IBW formulas assume standard skeletal structure. Adjusted formulas exist for amputees that account for the weight of missing limbs — standard IBW calculators are not appropriate in these cases.

Who Uses This

• Individuals setting a general weight goal who want a reference range based on their height and gender
• Healthcare professionals using IBW for initial medication dosing estimates, particularly for drugs where dosing is based on ideal rather than actual body weight
• Fitness and nutrition coaches establishing a starting reference point before assessing body composition
• Athletes and sports competitors checking weight classifications relevant to their sport
• Parents and caregivers checking whether a child’s weight falls within a healthy range for their height and age

Ideal Weight vs. BMI

BMI and IBW formulas both use height and weight but answer slightly different questions. IBW formulas produce a single target weight or a narrow range. BMI produces a ratio that places a person in a category — underweight, normal, overweight, or obese — based on their current weight relative to height.

Neither accounts for body composition. A muscular person can have a high BMI without excess fat, and a thin person can have a “normal” BMI while carrying an unhealthy proportion of body fat. Both measures are useful screening tools — not diagnostic tests — and should be interpreted alongside other health indicators.

FAQ

What is the ideal weight for my height?

It depends on your gender and the formula used. For a quick reference at 75% confidence across formulas: multiply your height in metres squared by 21.75 (the midpoint of the healthy BMI range) to get a central estimate. For example, at 165 cm: 1.65² × 21.75 = approximately 59 kg.

Which ideal weight formula is most accurate?

The Devine formula is the most widely used in clinical settings, particularly for medication dosing. The Robinson and Miller formulas are modifications that some researchers consider more reflective of contemporary populations. No single formula is universally more accurate — the healthy BMI range is often the most practical reference for general health purposes.

Should I aim for my ideal body weight?

IBW is a reference point, not a prescription. Being slightly above or below formula-derived IBW is not inherently a health problem. Sustainable healthy habits — consistent exercise, a varied diet, adequate sleep — matter more than hitting a specific number.

Is ideal weight different for men and women at the same height?

Yes. All four formulas produce different values for men and women at the same height, reflecting differences in average muscle mass, bone density, and body composition between sexes.

How does age affect ideal weight?

The formulas themselves do not change with age for adults. However, as muscle mass naturally decreases with age, the weight at which a person is healthiest may shift — making body composition monitoring (rather than scale weight alone) increasingly important with age.

A Note on Results

Ideal body weight formulas are general estimation tools developed primarily for clinical dosage calculations — not for defining a personal health target. Being above or below formula-derived IBW does not indicate poor health, and no formula can account for individual variation in muscle mass, bone density, genetics, or health conditions. Use these results as one data point among many, and speak with a healthcare provider for personalised guidance on healthy weight for your specific situation.