Free Ideal Weight Calculator

Many people want to know what their ideal weight should be, but the answer is not a single number. Health professionals define an ideal body weight (IBW) as the weight associated with the lowest mortality risk for a given height and sex. This free ideal body weight calculator uses your height and sex along with six classical formulas — including the widely adopted Devine formula — plus the Peterson formula that relies on a target BMI, to give you a full picture of your healthy weight range.

How the IBW Calculator Works

The calculator is designed for ease of use. You start by selecting your unit system (metric or imperial). Your sex is recorded once and saved for subsequent visits. Then you enter your height, which must be between 153 cm (5 ft) and 272 cm (8.9 ft) for the algorithms to function correctly. After that, you provide your current weight (minimum 15 kg / 33 lb, maximum 635 kg / 1400 lb). Once all data is entered, the tool instantly computes your IBW according to every formula and displays the results in a table and an interactive graph.

In addition to the formula‑based numbers, the calculator derives a healthy weight range based on your BMI, using the standard normal BMI interval of 18.5–24.9. This range acts as a quick reference: if your current weight falls inside it, you are likely in a low‑risk zone; if it does not, the tool shows exactly how many kilograms you would need to gain or lose to reach either boundary.

The Six Classical Formulas

Below are the equations used for men and women. All formulas that use inches rely on a baseline for 5 feet (152.4 cm) and add a certain amount for each extra inch.

For Men

Formula	Calculation (kg)
Robinson	$52 + 1.9 \times ( \text{inches over 5 ft} )$
Miller	$56.2 + 1.41 \times ( \text{inches over 5 ft} )$
Hamwi	$48.0 + 2.7 \times ( \text{inches over 5 ft} )$
Devine	$50.0 + 2.3 \times ( \text{inches over 5 ft} )$
Broca	$\text{height (cm)} - 100$
Lorentz	$(\text{height (cm)} - 100) - \dfrac{\text{height (cm)} - 150}{4}$

For Women

Formula	Calculation (kg)
Robinson	$49 + 1.7 \times ( \text{inches over 5 ft} )$
Miller	$53.1 + 1.36 \times ( \text{inches over 5 ft} )$
Hamwi	$45.5 + 2.2 \times ( \text{inches over 5 ft} )$
Devine	$45.5 + 2.3 \times ( \text{inches over 5 ft} )$
Broca	$\text{height (cm)} - 100$
Lorentz	$(\text{height (cm)} - 100) - \dfrac{\text{height (cm)} - 150}{2}$

The Devine formula has the strongest clinical evidence and is commonly used to calculate doses of drugs such as levothyroxine and immunoglobulins. Robinson and Miller are sometimes considered refinements of Devine, while Hamwi tends to produce higher estimates, especially for taller individuals.

Understanding Formula Differences

The spread among the six formulas can be surprising at first. For a 183 cm man, the estimates range from 73 kg (Miller) to 83 kg (Broca) — a 10 kg difference. This variation occurs because each formula uses different baseline weight for 5 feet and different increments per inch. For instance, Miller uses a higher baseline (56.2 kg) but a smaller increment (1.41 kg), making it more suitable for people with a slender build, whereas Hamwi uses a relatively low baseline (48.0 kg) but a large increment (2.7 kg), which can overestimate ideal weight for very tall individuals. Understanding these tendencies helps you pick the formula that best matches your body type.

The Peterson Formula

The Peterson formula differs from the classical ones because it incorporates a customizable target BMI rather than a fixed increment:

$$\text{IBW} = (2.2 \times \text{BMI}_{\text{target}}) + (3.5 \times \text{BMI}_{\text{target}} \times (\text{height}_{\text{m}} - 1.5))$$

By default, the calculator uses a target BMI of 22, but you can adjust this value (e.g., to 25) to see how your ideal weight would change. This formula is independent of sex, making it a universal option.

Example Application

Take the case of a 6‑foot (183 cm) male who currently weighs 80 kg. The calculator returns these ideal weights:

• Peterson (target BMI 22): 74 kg
• Miller: 73 kg
• Robinson: 75 kg
• Devine: 78 kg
• Hamwi: 81 kg
• Broca: 83 kg
• Lorentz: 75 kg

Additionally, the healthy BMI range corresponds to a weight interval of 62–83 kg (137–183 lb). If the target BMI is raised to 25, the Peterson value becomes 84 kg. This example shows that even for the same person, different formulas can suggest slightly different targets, which is why seeing the full set is helpful.

Understanding the Healthy Weight Range

Body Mass Index is defined as:

$$\text{BMI} = \dfrac{\text{weight (kg)}}{\left(\text{height (m)}\right)^{2}}$$

The normal BMI span (18.5–24.9) translates into the following weight limits for a given height:

$$\text{Weight}_{\text{lower}} = 18.5 \times (\text{height}_{\text{m}})^{2}, \quad \text{Weight}_{\text{upper}} = 24.9 \times (\text{height}_{\text{m}})^{2}$$

For example, for a height of 1.70 m, the healthy range would be approximately 53.5–72 kg. Staying inside this range is generally associated with lower risks of cardiovascular disease, diabetes, and other weight‑related conditions.

Interpretation and Limitations

While the calculator provides multiple numbers, it is important to understand that no formula can capture individual differences such as muscle mass, bone density, age, or ethnicity. People with high lean body mass (e.g., athletes) may have a true healthy weight that exceeds the formula predictions. Conversely, those with low muscle mass might need to be toward the lower end of the range.

The IBW calculator is designed for non‑pregnant adults only. For children and teenagers, growth percentiles are more appropriate. Pregnant women should follow specialised weight gain guidelines rather than relying on IBW formulas.

It is also crucial to remember that these formulas were originally created for medical purposes — mainly to standardise drug dosages — not as strict targets for body aesthetics or performance. If your current weight is already within the healthy BMI range, there is usually no medical imperative to adjust it to match a specific formula number.

Why Six Formulas?

Different formulas exist because they were derived from different populations and at different times. By presenting all of them, the calculator avoids the arbitrary choice of a single equation. You can look for the common cluster of values and use it as a realistic goal. This approach reinforces the idea that ideal weight is not a fixed point but a range, and that maintaining a healthy lifestyle matters more than hitting an exact number on the scale.