Ideal body weight:
a healthy range for your height

What ideal body weight means, and what it does not

Ideal body weight is a reference figure for a given height, produced by a simple formula. It was never designed as a verdict on whether you are healthy, and it cannot account for frame, muscle, age or medical history.

Several formulas exist and they disagree with each other. That alone tells you the figure is a range of reasonable weights, not a single correct number.

Heights and weights also change with age. A figure that suits a 25-year-old may not describe a healthy weight at 65, and unintended weight loss in later life deserves a doctor's attention.

The most useful way to think of it is a healthy range for your height, which you can cross-check with your waist measurement and how you feel.

Ideal body weight formulas: Devine and the BMI range

The Devine formula is one of the best known. It was devised in the 1970s to help estimate drug doses, and it counts inches above 5 feet (60 inches).

The second approach is the healthy-weight range implied by BMI. Multiply the squared height in metres by the lower and upper limits of the healthy band, 18.5 and 24.9.

Three other well-known formulas follow the same pattern with different constants: Robinson, Miller and Hamwi. They all start from 5 feet and add a fixed amount for each extra inch, which is why they sit within a few kilograms of one another at average heights.

How to find your own healthy weight range

1. 1Measure your height without shoes, standing straight, and note it in centimetres.
2. 2Divide by 100 to convert to metres, then square the result.
3. 3Multiply by 18.5 for the lower end of the range and by 24.9 for the upper end.
4. 4Divide your height in cm by 2 to get an upper limit for your waist, in cm, as a quick cross-check.

For 170 cm, that gives a squared height of 2.89, a range of 53.5 to 72.0 kg and a waist limit of 85 cm. Compare the results with where you are today before drawing any conclusions.

Write the range down as a band, not a point. Weights inside it can look very different from person to person, and the band is wide on purpose.

Worked example: a woman 165 cm tall

1. 1Convert height to inches: 165 ÷ 2.54 = 64.96 in.
2. 2Subtract 60 to find the inches over 5 ft: 4.96 in.
3. 3Apply the Devine formula for women: 45.5 + 2.3 × 4.96.
4. 4Compare with the BMI range for 1.65 m.

The Devine figure sits comfortably inside the range, a little below its midpoint. A person at 67 kg is still in the healthy band at this height, which is why a single target can be misleading.

Ideal weight chart by height (150 – 185 cm)

Reading across a row shows how much the formulas differ. At 170 cm the BMI range spans almost 19 kg, while the two Devine figures are about 4.5 kg apart. The single numbers are narrower than the truth, which is a good reason to prefer the range.

Use the range column as your main guide. The Devine columns are single reference points, and they differ from each other by about 4.5 kg at every height because the starting constants differ.

Waist size gives a useful cross-check. A waist-to-height ratio below 0.5 is a commonly used benchmark, which for a person 165 cm tall means a waist under 82.5 cm. The waist-to-height ratio calculator on this page does the sum for you.

Where ideal weight formulas fall short

• They ignore muscle. A person who trains regularly can sit above the 'ideal' without carrying excess fat.
• They ignore frame size and bone structure, which vary a lot between people of the same height.
• They were not designed with South Asian populations in mind, where health risks can begin at lower weights.
• They are not meant for children, teenagers or pregnancy, and are less certain for older adults.
• They say nothing about blood sugar, blood pressure or fitness, which are measured separately.

For adults of South Asian origin, several Indian guidelines suggest earlier BMI thresholds, with overweight starting from 23. At 165 cm, a BMI of 23 corresponds to about 62.6 kg, a good reason to read the upper end of any chart with caution and to ask your doctor which scale suits you.

Using an ideal weight figure well

Before comparing yourself with any table, measure honestly. Height shrinks slightly through the day and with age, so measuring in the morning, without shoes, and against a wall gives a figure you can reuse.

Use the range as context, not a deadline. If you are inside it, there is no need to chase the lower end. If you are above it, a gradual change over months, guided by health markers rather than a number alone, is the sensible route.

A second example shows how wide the band is for taller people. For a man 178 cm tall, the Devine formula gives 73.2 kg, while the BMI range runs from 58.6 kg to 78.9 kg, a spread of more than 20 kg.

Think in terms of what you want to be able to do: climb stairs comfortably, sleep well, manage blood sugar. Weight is one input to those goals, not the goal itself.

If your reading is far outside the range, or you are underweight, speak to a doctor. Being too low is as much a health matter as being too high, and a formula cannot tell you why you are where you are.

The BMI guide on this site explains the categories behind the 18.5 and 24.9 limits in more detail.