Ideal Weight Calculator
Example 1
A 30-year-old woman with a height of 1.65 m wants to estimate her ideal body weight using both the Devine and Robinson formulas. Her height in inches is 165 ÷ 2.54 = 65.0 inches, which is 5 inches above the 5-foot (60-inch) reference height.
Solution
Apply the Devine formula for women: ideal weight = 45.5 + 2.3 × (height in inches − 60).
Apply the Robinson formula for women: ideal weight = 49 + 1.7 × (height in inches − 60).
Both formulas produce nearly identical results for this height, which is common for women close to the 5-foot reference height.
Answer
57 to 58 kg is the ideal weight range for this height using the Devine formula. For a 1.65 m woman, both formulas agree closely, giving a target of approximately 57 to 58 kg.
Source: Devine BJ, Gentamicin Therapy. Drug Intelligence & Clinical Pharmacy, 1974
Example 2
A 40-year-old man who is 1.80 m tall wants to know his ideal weight using the Devine and Robinson formulas. His height in inches is 180 ÷ 2.54 = 70.87 inches, which is 10.87 inches above the 5-foot reference height.
Solution
Apply the Devine formula for men: ideal weight = 50 + 2.3 × (height in inches − 60).
Apply the Robinson formula for men: ideal weight = 52 + 1.9 × (height in inches − 60).
The Devine formula produces a higher estimate than the Robinson formula for this height, which is expected since the Devine formula uses a larger per-inch increment.
Answer
75 kg is the ideal weight for a 1.80 m man using the Devine formula. The Robinson formula gives 72.7 kg. The healthy BMI range for this height is 59.9 to 80.6 kg.
Example 3
A person with a BMI of 27 and a waist circumference of 95 cm wants to understand their target weight range. Their height is 1.70 m and their current weight is 78 kg. The healthy BMI range is 18.5 to 24.9.
Solution
Calculate the healthy weight range for a height of 1.70 m. The healthy BMI range is 18.5 to 24.9.
Their current weight of 78 kg corresponds to a BMI of 78 ÷ 2.89 = 27.0, which is in the overweight category. They need to lose between 6 kg (to reach 72 kg, the upper end) and 24 kg (to reach 54 kg, the lower end).
Answer
For a height of 1.70 m, the healthy BMI range of 18.5 to 24.9 corresponds to 53.5 to 72.0 kg. The current weight of 78 kg (BMI 27) is 6 kg above the healthy range, requiring a loss of at least 6 kg to reach the upper boundary.
Source: WHO: BMI Classification, 2024
Example 4
A 28-year-old man is 180 cm tall with a large frame. What is his ideal weight range using the Devine formula and frame adjustment?
Solution
Large frame adjustment (+10%): 75.2 × 1.10 = 82.7 kg.
Healthy BMI range (18.5-24.9) for 180 cm: 60.0-80.7 kg. With large frame, upper end is more appropriate.
Answer
Devine ideal: 75.2 kg. With large frame: 82.7 kg. BMI range: 60-81 kg.
Source: Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm, 1974
Published:
Updated:
References
- [1]CDC, Centers for Disease Control and Prevention - About Adult BMI. https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html
- [2]National Institutes of Health, National Heart, Lung, and Blood Institute - Assessing Your Weight and Health Risk. https://www.nhlbi.nih.gov/health/educational/lose_wt/risk.htm
- [3]Drug Intelligence Publications, Devine BJ - Gentamicin Therapy. Drug Intelligence & Clinical Pharmacy, 1974. https://pubmed.ncbi.nlm.nih.gov/4606809
Glossary
- Ideal body weight – An estimate of the weight associated with the lowest health risk for a given height and biological sex, used primarily for medication dosing and clinical reference.
- Devine formula – A formula developed in 1974 by Dr. Bernard Devine for calculating ideal body weight, originally for theophylline dosing. Uses 50 kg base for men and 45.5 kg for women at 5 feet, adding 2.3 kg per inch above 5 feet.
- Robinson formula – A formula published in 1983 derived from NHANES I survey data. Uses 52 kg base for men and 49 kg for women at 5 feet, adding 1.9 kg per inch for men and 1.7 kg per inch for women.
- Miller formula – A formula published in 1983 that uses a smaller per-inch increment than Devine and Robinson, giving lower estimates for taller individuals. Base weights of 56.2 kg for men and 53.1 kg for women.
- Hamwi formula – A formula developed in 1964 for dietetics reference, using a larger per-inch increment. Base weights of 48 kg for men and 45.5 kg for women, adding 2.7 kg per inch for men and 2.2 kg per inch for women.
- Body Mass Index (BMI) – A measure of body fat based on height and weight, calculated as weight in kilograms divided by height in metres squared. WHO classifies BMI below 18.5 as underweight, 18.5 to 24.9 as normal, and 25.0 and above as overweight.
- Healthy weight range – The weight range corresponding to a BMI of 18.5 to 24.9, as defined by the WHO. Unlike ideal weight formulas, this is a range rather than a single number.
- Frame size – An individual's bone structure size, typically classified as small, medium, or large. Frame size affects the relationship between height and healthy weight but is not accounted for in standard ideal weight formulas.
- Lean body mass – The total mass of the body minus body fat, consisting of muscle, bone, organs, and water. Ideal weight formulas aim to estimate lean body mass range for medication dosing purposes.
- Adjusted body weight – A modified weight used for obese patients in clinical dosing, calculated as ideal body weight plus a fraction of the excess weight. Commonly used when actual weight exceeds ideal weight by more than 20 percent.
How to Use?
- 1
Enter your height
Type your height into the height field. Use the unit dropdown to switch between centimetres (cm), feet (ft), or inches (in). The calculator converts to centimetres automatically.
- 2
Select your biological sex
Choose male or female from the dropdown. The Devine and Robinson formulas use different base weights and increments for each sex.
- 3
Review your ideal weight estimates
The calculator displays the Devine formula estimate, Robinson formula estimate, and healthy BMI minimum and maximum. Switch between kilograms, pounds, and stone using the unit dropdown on any result.
- 4
Compare the estimates on the visual scale
The coloured BMI scale shows where the Devine formula estimate falls relative to the WHO classification categories. The bar chart below the estimates compares all four values side by side for quick visual comparison.
- 5
Use the estimates as a reference range
Your personal healthy weight is likely somewhere between the Devine and Robinson estimates and within the BMI range. Do not fixate on a single number. Combine these estimates with body composition, waist circumference, and blood work for a complete health picture.
Frequently Asked Questions
Ideal body weight (IBW) is an estimate of the weight that is associated with the lowest health risk for a given height and biological sex. It is determined using population-level formulas, the widely used being the Devine and Robinson formulas. Both calculate a base weight for a height of 5 feet (152.4 cm) and add a fixed amount per inch above that height. The Devine formula adds 2.3 kg per inch for both sexes, while the Robinson formula adds 1.9 kg per inch for men and 1.7 kg per inch for women. These estimates are reference points for clinicians, not precise individual targets.
The Devine formula calculates ideal weight as 50 kg for men at 5 feet plus 2.3 kg per inch above 5 feet, and 45.5 kg for women at 5 feet plus 2.3 kg per inch above 5 feet. It was published in 1974 by Dr. Bernard Devine for calculating theophylline doses in respiratory medicine. It has since become a widely used ideal weight formula in clinical practice, particularly for medication dosing in anaesthesia, critical care, and chemotherapy. The formula is simple but was never validated for general health assessment, which is why it should be used alongside the healthy BMI range.
The Robinson formula calculates ideal weight as 52 kg for men at 5 feet plus 1.9 kg per inch above 5 feet, and 49 kg for women at 5 feet plus 1.7 kg per inch above 5 feet. It was published in 1983 by Dr. Robinson and colleagues using data from the first National Health and Nutrition Examination Survey (NHANES I). Because the formula was derived from a nationally representative sample, it is often preferred in nutrition research and dietetics. The Robinson formula tends to give higher estimates for shorter individuals and lower estimates for taller individuals compared to the Devine formula.
Neither formula is definitively more accurate because both are population-level estimates with substantial individual variation. The Devine formula is the clinical standard for medication dosing and is recommended by major anaesthesia and critical care guidelines. The Robinson formula is more commonly used in nutrition research because it was derived from a representative population survey. In practice, the two formulas typically produce estimates within 2 to 5 kg of each other, and the true healthy weight for an individual depends on muscle mass, bone density, frame size, and overall body composition. The most useful approach is to use the range between the two estimates as your target zone.
Ideal weight is a single number produced by a formula such as Devine or Robinson. Healthy weight is the entire weight range corresponding to a BMI of 18.5 to 24.9, as defined by the WHO. A person with a height of 170 cm has a healthy weight range of 53.5 to 72.0 kg, while their Devine estimate (for a male) is 66.5 kg. The two concepts serve different purposes: ideal weight formulas give a clinical reference point for dosing and screening, while the healthy BMI range gives a wider target zone associated with the lowest population-level mortality. For personal weight goals, the healthy BMI range is more useful because it accounts for individual variation.
Yes, ideal weight estimates can serve as reference points for setting realistic weight loss or gain targets, but they should not be the sole determinant. A reasonable approach is to aim for a weight within the healthy BMI range, using the ideal formula estimates as rough guidelines. If your current weight is above the healthy BMI maximum, set an initial goal of reaching the upper end of the range, then reassess. Always combine weight targets with body composition assessment. Losing weight while preserving muscle mass is more important than reaching a specific number on the scale.
No, ideal weight formulas do not account for muscle mass, bone density, or body composition. They use only height and biological sex to produce an estimate. This is their most significant limitation. A muscular athlete and a sedentary person of the same height and sex receive the same ideal weight estimate, even though muscular individuals typically weigh more and have healthier body composition. If you are physically active and have significant muscle mass, your healthy weight may be 5 to 15 kg above the formula estimate. Body fat percentage measured by skinfold calipers or bioelectrical impedance provides a more accurate assessment.
The standard Devine and Robinson formulas do not include ethnicity adjustments, and no widely accepted ethnicity-specific versions exist. Research suggests that the relationship between height, muscle mass, and body fat varies across ethnic groups, which may affect the accuracy of ideal weight estimates. People of Asian descent tend to have higher body fat percentages at the same BMI and may have lower optimal weights than the formula estimates. People of African descent may have higher bone density and muscle mass, potentially making the formula estimates conservative. The healthy BMI range provides a more flexible target zone that partially addresses these differences, but individuals should discuss personalised weight targets with their healthcare provider.
Ideal weight formulas are less applicable to athletes and bodybuilders because these individuals have significantly more muscle mass than the general population. A male bodybuilder with a height of 180 cm may weigh 90 to 100 kg with very low body fat, which is well above his Devine estimate of 69.8 kg. This does not mean he is overweight; it means the formula does not account for his muscle mass. Athletes should use body fat percentage as their primary body composition metric rather than weight-based formulas. The ideal weight estimates on this page are provided as general reference only and should not be used as health targets for highly muscular individuals.
The Devine and Robinson formulas were developed for general adult populations and may be less appropriate for older adults. After age 30, adults lose 3 to 8% of their muscle mass per decade, which changes body composition even if weight remains stable. A 75-year-old who achieves the same weight as their 30-year-old ideal estimate may have more body fat and less muscle than is healthy. Some geriatric guidelines recommend a slightly higher BMI target of 24 to 27 for adults over 65, as a modest amount of body fat provides metabolic reserve during illness and a slightly higher weight correlates with better outcomes. Older users should discuss weight targets with a healthcare provider who can assess their individual muscle mass and functional status.
Stand against a wall with your heels, buttocks, and shoulders touching the surface. Remove your shoes. Look straight ahead so your line of sight is horizontal. Place a flat object such as a book or ruler on top of your head, perpendicular to the wall. Mark the wall at the bottom edge of the object. Measure from the floor to the mark using a tape measure. Record your height to the nearest 0.1 cm or 0.1 inch. Do not estimate your height by looking down at a tape measure, as this introduces parallax error of 1 to 3 cm.
No, the formulas use different base weights and per-inch increments for men and women. For the Devine formula, men start at 50 kg at 5 feet and women start at 45.5 kg. The per-inch increment of 2.3 kg is the same for both sexes. For the Robinson formula, men start at 52 kg with an increment of 1.9 kg per inch, while women start at 49 kg with an increment of 1.7 kg per inch. These differences reflect average differences in body composition, muscle mass, and fat distribution between sexes. At the same height, the male estimate is always higher than the female estimate, typically by 4 to 8 kg depending on the formula.
Ideal weight estimates do not change unless your height changes, which is rare in adults. You only need to recalculate if you want to see the estimates in a different unit or if your height changes due to conditions such as spinal compression from aging, scoliosis, or vertebral fractures. The more useful practice is to track your actual body weight relative to the healthy BMI range over time. Checking your weight once per month and comparing it to your target range gives you a meaningful trend. A gradual drift toward the upper end of the range signals the need for preventive action, while a stable weight within the range confirms that you are maintaining a healthy weight.
Your ideal weight estimate does not change unless your height changes because the formulas use only height and biological sex. However, your personal optimal weight can and should change as you age. As muscle mass declines and body composition shifts, the weight that is healthiest for you may differ from the formula estimate. For example, an active 30-year-old may thrive at 3 kg above their Devine estimate because they carry significant muscle mass, while the same person at 70 with reduced muscle mass may be healthier 2 kg below their Devine estimate. The static nature of the formulas is a limitation, which is why they should be treated as reference points rather than targets.
Yes, discussing weight targets with a healthcare provider is recommended, especially if you have underlying health conditions, are taking medications, or are planning significant weight changes. A doctor can assess your individual risk factors, review your blood work, measure your waist circumference and body fat, and help you set a personalised weight target that accounts for your muscle mass, bone density, medical history, and lifestyle. This calculator provides population-level estimates that are useful for general reference but should not replace personalised medical advice. Always consult a qualified healthcare provider before starting a weight management programme.
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