The Devine formula - the most medically cited - gives an ideal body weight of 67.7 kg (149 lb) for a 170 cm (5'7") male and 63.2 kg (139 lb) for a female. The WHO-recommended healthy BMI range (18.5–24.9) is broader: 53.5–72.1 kg (118–159 lb) for 170 cm. IBW formulas were designed for drug dosing - they are reference points, not prescriptions.
How to use this ibw calculator
Select your unit system and sex, then enter your height. The Devine ideal body weight, the healthy BMI range (18.5–24.9 kg/m²), and three comparison formula estimates appear instantly. Optionally enter your current weight to see how far above or below the Devine IBW you are.
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What is ideal body weight?
Ideal body weight (IBW) is a height- and sex-based weight estimate used primarily in clinical pharmacokinetics to calculate drug dosages. The concept was popularised by Benjamin Devine in 1974 to determine the correct dose of gentamicin - an antibiotic whose distribution in the body follows lean mass rather than total mass.
The term "ideal" is misleading in a fitness context. The Devine formula was not derived from population health data or body composition studies - it was a clinical approximation for medication dosing. Modern usage has expanded beyond its intended scope, but IBW remains a useful starting point for understanding healthy weight ranges.
For most adults, the WHO healthy BMI range of 18.5–24.9 is a more evidence-based target than any single IBW formula, because it is derived from large-scale epidemiological data linking BMI to health outcomes.
IBW formulas compared
Four formulas are in common use. All share the same structure: a base weight (for someone exactly 5 feet / 152.4 cm tall) plus a fixed increment per inch of height above 5 feet.
| Formula | Year | Male base + per inch | Female base + per inch | Original purpose |
|---|---|---|---|---|
| Devine | 1974 | 50.0 kg + 2.3 kg/in | 45.5 kg + 2.3 kg/in | Gentamicin dosing |
| Robinson | 1983 | 52.0 kg + 1.9 kg/in | 49.0 kg + 1.7 kg/in | General drug dosing |
| Miller | 1983 | 56.2 kg + 1.41 kg/in | 53.1 kg + 1.36 kg/in | General drug dosing |
| Hamwi | 1964 | 48.0 kg + 2.7 kg/in | 45.5 kg + 2.2 kg/in | Diabetes dietary planning |
The Devine formula (1974)
The most clinically cited formula. Medicine cites the Devine formula most often because it is the standard for calculating drug doses, not because it offers a more accurate view of a healthy weight than the other formulas.
For men:
$$\text{IBW}_{\text{male}} = 50.0 + 2.3 \times (\text{height (in)} - 60)$$
For women:
$$\text{IBW}_{\text{female}} = 45.5 + 2.3 \times (\text{height (in)} - 60)$$
Where height is measured in inches and 60 represents 5 feet (the formula's baseline). At exactly 5'0" (152.4 cm), IBW equals the base weight: 50.0 kg for men and 45.5 kg for women.
The Robinson formula (1983)
The Robinson formula was an attempt to refine the Devine formula by applying a more rigorous statistical analysis to the same data. It is generally considered more accurate for people of average height, though it tends to underestimate weight for very tall men.
The per-inch increment is lower (1.9 kg/in for men vs 2.3 kg/in in Devine), making Robinson give slightly lower IBW values for taller individuals.
For men:
$$\text{IBW}_{\text{male}} = 52.0 + 1.9 \times (\text{height (in)} - 60)$$
For women:
$$\text{IBW}_{\text{female}} = 49.0 + 1.7 \times (\text{height (in)} - 60)$$
Key differences
- The Starting Point: Robinson starts men at 52 kg and women at 49 kg for the first 5 feet.
- The Scaling: For every inch over 5 feet, it adds 1.9 kg for men and 1.7 kg for women.
Robinson formula comparison
Because these increments (1.9 and 1.7) are lower than Devine’s (2.3 for both), the Robinson formula will give you a "lighter" ideal weight the taller you get.
The Miller formula (1983)
The Miller formula was developed as an alternative to the Devine model by re-evaluating the same clinical data. It is unique because it sets a higher base weight for individuals at 5 feet tall but uses a much lower weight increase for every inch after that.
For men:
$$\text{IBW}_{\text{male}} = 56.2 + 1.41 \times (\text{height (in)} - 60)$$
For women:
$$\text{IBW}_{\text{female}} = 53.1 + 1.36 \times (\text{height (in)} - 60)$$
While a 5'0" male starts at 56.2 kg (the highest base weight of the four formulas), the low per-inch increment means the ideal weight scales more slowly. This makes the Miller formula generally more conservative for taller individuals compared to the Devine or Hamwi methods.
The Hamwi formula (1964)
Commonly referred to as the "rule of thumb" method, the Hamwi formula is popular because of its simplicity. Like others, it uses a base weight for the first 5 feet of height and adds a set amount for every additional inch.
For men:
$$\text{IBW}_{\text{male}} = 48.0 + 2.7 \times (\text{height (in)} - 60)$$
For women:
$$\text{IBW}_{\text{female}} = 45.5 + 2.2 \times (\text{height (in)} - 60)$$
Where height is measured in inches and 60 represents the 5 foot baseline. At exactly 5'0", the ideal weight is 48.0 kg for men and 45.5 kg for women. Since the male increment of 2.7 kg per inch is the highest among these common formulas, Hamwi tends to predict higher ideal weights for taller men.
Why the formulas differ
Each formula was derived from a different patient sample using regression analysis. The 2-5 kg spread between formulas at typical adult heights reflects statistical variation between samples rather than a meaningful clinical difference. In practice, all four formulas give broadly similar guidance - the choice of formula rarely matters more than ±5% of body weight.
Healthy weight range (BMI method)
The WHO defines a healthy adult weight as BMI between 18.5 and 24.9 kg/m². Converting this to a weight range for a given height:
$$\text{Healthy weight} = \text{BMI} \times \text{height (m)}^2, \quad \text{BMI} \in [18.5,\, 24.9]$$
This gives a range rather than a single "ideal" point - a more realistic and better-validated target than any IBW formula.
| Height | BMI healthy min (18.5) | BMI healthy max (24.9) | Devine IBW (male) | Devine IBW (female) |
|---|---|---|---|---|
| 155 cm (5'1") | 44.4 kg (98 lb) | 59.8 kg (132 lb) | 50.0 kg (110 lb) | 45.5 kg (100 lb) |
| 160 cm (5'3") | 47.4 kg (104 lb) | 63.7 kg (140 lb) | 51.5 kg (114 lb) | 47.1 kg (104 lb) |
| 165 cm (5'5") | 50.4 kg (111 lb) | 67.8 kg (149 lb) | 55.0 kg (121 lb) | 50.5 kg (111 lb) |
| 170 cm (5'7") | 53.5 kg (118 lb) | 72.1 kg (159 lb) | 67.7 kg (149 lb) | 63.2 kg (139 lb) |
| 175 cm (5'9") | 56.7 kg (125 lb) | 76.3 kg (168 lb) | 72.6 kg (160 lb) | 68.1 kg (150 lb) |
| 180 cm (5'11") | 59.9 kg (132 lb) | 80.7 kg (178 lb) | 77.5 kg (171 lb) | 73.0 kg (161 lb) |
| 185 cm (6'1") | 63.3 kg (140 lb) | 85.2 kg (188 lb) | 82.4 kg (182 lb) | 77.9 kg (172 lb) |
| 190 cm (6'3") | 66.8 kg (147 lb) | 89.9 kg (198 lb) | 87.3 kg (192 lb) | 82.8 kg (183 lb) |
Limitations of IBW
IBW formulas have four important limitations that make them poor personal health targets without additional context.
No distinction between muscle and fat
A 180 cm male athlete with 85 kg body weight and 10% body fat has an FFMI of approximately 23 - well-muscled and healthy by any body composition measure. Yet the Devine formula says his "ideal weight" is 77.5 kg. The formula cannot distinguish muscle from fat, so muscular individuals will consistently appear "overweight" against their IBW.
Age is not considered
Evidence suggests adults over 65 benefit from a slightly higher BMI (23–27.5) than the standard healthy range, due to reduced sarcopenia risk and improved survival outcomes. IBW formulas do not adjust for age. For older adults, erring toward the higher end of the healthy BMI range is typically more appropriate than targeting a single IBW.
Ethnicity thresholds differ
WHO Asian-specific BMI cut-offs recommend overweight from 23.0 and obesity from 27.5 - lower than the standard 25.0 and 30.0 thresholds. This affects what constitutes a healthy weight range for individuals of East and South Asian descent. IBW formulas do not incorporate ethnicity.
Frame size is not captured
Hamwi's original formulation included small, medium, and large frame adjustments (±10% of the base). Most online calculators - including this one - use the medium-frame values only. Individuals with genuinely large or small bone structures may find the default IBW systematically high or low by several kilograms.
FAQs
What is the most accurate ideal weight formula?
No IBW formula is more "accurate" in a biological sense - all are regression approximations from older clinical populations. The Devine formula is the most widely cited in medicine because drug dosing protocols reference it, not because it better predicts a healthy weight. For personal health decisions, the WHO BMI range (18.5–24.9) is the more evidence-based target.
What is a healthy weight for my height?
Use the BMI range: multiply your height in metres squared by 18.5 (minimum) and 24.9 (maximum). For 170 cm: 1.70² = 2.89; 2.89 × 18.5 = 53.5 kg minimum, 2.89 × 24.9 = 72.0 kg maximum. This 18.5 kg range is your healthy weight band, within which any weight is considered clinically normal.
Do IBW formulas work for heights under 5 feet?
The formulas still compute a number below 5 feet (152.4 cm), but they become less reliable because the original regression data had few subjects in this range. The per-inch coefficient turns negative below 5 feet, reducing IBW by that coefficient for each inch below the baseline. For individuals under 5 feet, the BMI healthy range is more defensible than any single IBW formula.
Should I try to reach my IBW?
IBW is a reference point, not a prescription. If your weight falls anywhere within the healthy BMI range (18.5–24.9), your weight is clinically normal regardless of IBW. Athletes and muscular individuals will often exceed IBW while being in excellent health. Rather than targeting a specific IBW number, aim for the healthy BMI range and consult a healthcare professional for personalised guidance.
Why do the Robinson and Miller formulas give different results from Devine?
All three were derived from the same underlying dataset (Metropolitan Life Insurance height-weight tables) but used different regression methods and made different adjustments. Robinson gives slightly lower values for tall people (1.9 kg/in vs 2.3 kg/in increment). Miller gives the highest base weights but the lowest per-inch increment. The 2–5 kg difference between formulas at typical adult heights is clinically negligible.
How does ideal weight relate to BMI?
The Devine IBW corresponds to different BMIs at different heights. For a 170 cm male, Devine IBW of 67.7 kg gives BMI = 67.7 / 1.70² = 23.4 - squarely in the healthy range. For a 190 cm male, Devine IBW of 87.3 kg gives BMI = 87.3 / 1.90² = 24.2. The formulas are implicitly calibrated to keep IBW within the healthy BMI range for typical adult heights.
How much should I weigh?
There is no single "ideal" weight that fits everyone. Health professionals generally view a healthy weight as a range rather than a specific target number. This is because factors like your body composition, muscle mass, age, and genetic makeup heavily influence what is healthy for your specific body.
Calculators like these are helpful tools for finding a starting point or tracking progress, but they have limitations. For example, they often do not distinguish between body fat and muscle. An athlete with a high level of muscle mass might weigh more than these formulas predict, even while maintaining excellent health.
The most effective approach is to focus on a weight that supports your daily life, allows you to maintain consistent energy levels, and is sustainable through healthy habits. If you have specific concerns about your weight or health, talking with a doctor or a registered dietitian is the best way to get personalized advice tailored to your needs.