Ideal Weight Calculator, Explained

After reading this you will know where the four classic "ideal weight" formulas come from, why they disagree by a few kilograms, and how to read their output next to the wider BMI healthy range.

What the calculator does

The tool takes your height and sex and returns a single reference weight from four formulas: Devine, Robinson, Miller and Hamwi. It also shows the weight range that BMI marks as healthy for the same height, so you can compare a single target against a band.

Here is the hook. For a man 175 cm tall, the four formulas land between about 68 and 72 kg, while the BMI healthy range for that height runs from roughly 57 to 76 kg. One method hands you a point. The other hands you a span nearly 20 kg wide. Both describe the same body, and neither is a verdict.

These formulas were written to help clinicians pick drug doses that scale with lean body size, not to define how anyone should look. Treat the number as a dosing reference that happens to be labelled "ideal".

Where these formulas come from

All four share the same skeleton: a base weight at 5 feet (152.4 cm) plus a fixed increment for each inch above that. They differ only in the base and the increment, and each was fitted to a different dataset.

Hamwi (1964): The oldest, built as a bedside shortcut for insulin dosing. Largest per-inch increment, so it climbs fastest with height.
Devine (1974): Written for drug dosing and now the most widely cited. It became the de facto standard in pharmacy.
Robinson (1983): A re-fit of Devine against different reference data. Lower base weights, so it usually gives the smallest number.
Miller (1983): Another re-fit from the same era, with a smaller per-inch step. It sits close to Robinson.

Because they all key off height above 5 feet, they agree almost exactly at 152.4 cm and spread apart as you get taller. That spread is the honest error bar on the whole idea.

The formula and the intuition

Each formula follows the same pattern. Let h_{in} be your height in inches and h_{in} \gt 60, since the increment applies only above 5 feet.

W = B + k \cdot (h_{in} - 60)

Here W is the ideal weight in kilograms, B is the base weight at 60 inches, and k is the weight added per inch above 60. The table below gives B and k for each formula and sex.

Base weight and per-inch increment, in kilograms
Formula	Male base B	Male step k	Female base B	Female step k
Hamwi	48.0	2.722	45.5	2.268
Devine	50.0	2.300	45.5	2.300
Robinson	52.0	1.900	49.0	1.700
Miller	56.2	1.410	53.1	1.360

The intuition is simple: taller people carry more lean mass, so the formulas add a roughly linear amount per inch. Hamwi adds the most (2.722 kg per inch for men), Miller the least (1.410 kg). At 6 inches above 5 feet that difference alone is about 7.9 kg, which is why tall readers see the widest spread.

A worked example with the demo data

Male, 175 cm

The demo uses the defaults: male, metric, height 175 cm. First convert height to inches.

Height in inches: 175 / 2.54 = 68.90 in.
Inches above 60: 68.90 - 60 = 8.90 in.
Devine: 50.0 + 2.300 × 8.90 = 70.5 kg.
Robinson: 52.0 + 1.900 × 8.90 = 68.9 kg.
Miller: 56.2 + 1.410 × 8.90 = 68.8 kg.
Hamwi: 48.0 + 2.722 × 8.90 = 72.2 kg.

The four targets run from 68.8 to 72.2 kg, a spread of 3.4 kg. For the BMI range, multiply the BMI limits by height in metres squared. Height is 1.75 m, so h^2 = 3.0625. The healthy band (BMI 18.5 to 24.9) is 18.5 × 3.0625 = 56.7 kg up to 24.9 × 3.0625 = 76.3 kg.

All four bars sit inside the BMI healthy range of 56.7 to 76.3 kg, clustered near its upper middle.

How the spread grows with height

The formulas match at 5 feet and fan out as height rises. The chart below plots each formula for a male from 150 to 200 cm. Watch Hamwi (steepest) pull away from Miller (flattest).

Devine weight rises about 0.9 kg per cm. The marker at 175 cm reads near 70.5 kg, matching the worked example.

To feel the spread yourself, use the widget below to move a single height slider and watch all four targets and the BMI band shift together.

Reading and interpreting the result

Treat the four numbers as a small cluster, not four competing answers. A fair summary is their midpoint. For the demo that is about 70.1 kg. The useful question is not "which formula is right" but "where does my current weight fall relative to the cluster and the BMI band".

If your weight sits inside the BMI band but above every formula target, that is common and not a problem on its own. The formulas describe a lean reference frame from the 1960s to 1980s. Muscle, a larger skeletal frame and normal body composition all push a healthy weight upward. The BMI band exists precisely to give that room: it is about 20 kg wide at 175 cm for a reason.

If you want a single anchor, use the midpoint of the four formulas, then treat the BMI band as the acceptable spread around it. Do not chase the lowest formula (usually Robinson or Miller) as a goal.

Common mistakes

A few errors turn a rough estimate into a misleading one.

Using it below 5 feet. At heights under 152.4 cm the increment term goes negative or is clamped to zero, and the formulas were never validated there. The output is unreliable for short stature.
Reading it as a health verdict. These numbers ignore muscle, frame and fat distribution entirely. A muscular 90 kg athlete and a sedentary 90 kg person get the same "excess" over target, which tells you nothing useful.
Mixing units. The base weights are in kilograms and the step is per inch. If you compute by hand, convert height to inches first, as in the worked example.
Applying adult formulas to children. They assume adult proportions. For a growing child use a percentile tool instead.

Do not use the gap between your weight and an "ideal" number to set a rapid weight-loss target. The formulas carry a spread of several kilograms and were built for dosing, not goal setting. Talk to a professional before making health decisions.

Related tools on this site

The BMI Calculator gives the healthy weight band shown here plus the WHO category. Because BMI cannot tell muscle from fat, pair it with the Body Fat Estimator (Navy Method) or the Waist-to-Hip and Waist-to-Height Calculator for a shape-based read. If your real goal is energy balance, the BMR and TDEE Calculator estimates daily calories, and the Macro Calculator splits those into grams. For drug-dosing style body-size numbers see the Body Surface Area Calculator, and for children use the Child Growth Percentile Calculator rather than any adult formula.

Frequently asked questions

Which ideal weight formula is most accurate?

None is "accurate" in the sense of measuring a fact, because ideal weight is a convention, not a measurement. Devine is the most widely used in clinical dosing. Robinson and Miller give lower numbers, Hamwi higher. Their spread at 175 cm is only about 3.4 kg, so the choice matters less than people expect.

Why do the formulas ignore my current weight?

They are functions of height and sex only. That is deliberate: they estimate a reference lean size for a given frame, not a target derived from where you are now. Compare your actual weight against the result separately.

My weight is above every formula but inside the BMI range. Is that bad?

Not on its own. The BMI healthy band at 175 cm runs from about 56.7 to 76.3 kg, and the formula targets cluster near 70 kg. Sitting between the targets and the top of the band is normal, especially with more muscle.

Can I use these formulas for a child?

No. They assume adult body proportions and are undefined or unreliable below 5 feet. Use a growth percentile tool built on WHO reference data for children.

Why do all four formulas use 5 feet as the starting point?

Each was published with a base weight at 152.4 cm and a per-inch increment above it. That shared design is why they agree at 5 feet and diverge as height rises: at 185 cm the Hamwi-to-Miller gap grows to about 10 kg.

Try it yourself in the tool