Ideal Weight Calculator

What "ideal weight" really means (and why there's no single perfect number)

Picture a 35-year-old woman who's 165 cm tall. She looks at a chart, sees "57 kg", and feels a little defeated because she's been 66 kg for years and feels fine. Is she doing something wrong? Probably not. The chart isn't a verdict. It's a rough estimate built from a formula, and formulas don't know her bones, her muscle, her job, or how she feels when she climbs stairs.

That's the honest starting point. "Ideal weight" is a shorthand for a weight that's statistically common among healthy adults of your height and sex. It isn't a target you've failed to hit, and it isn't one number. Even the people who invented these formulas never meant them as a personal goal for every body.

This calculator shows you a range, not a single figure, and it shows several formulas side by side so you can see how much they disagree. They do disagree, sometimes by 5 kg or more. That spread is useful information, because it tells you how fuzzy the whole idea is.

The four main formulas, explained simply

All four formulas start with the same idea: pick a base weight for someone who's 5 feet (152.4 cm) tall, then add a fixed amount for every inch above that. They differ in the base number and in how much they add per inch.

Devine (1974)

For men, 50 kg plus 2.3 kg for every inch over 5 feet. For women, 45.5 kg plus 2.3 kg per inch. It's the best known of the four, and it's the one most online calculators use.

Robinson (1983)

For men, 52 kg plus 1.9 kg per inch over 5 feet. For women, 49 kg plus 1.7 kg per inch. Robinson starts a little higher but adds less per inch, so it gives lower numbers for tall people than Devine does.

Miller (1983)

For men, 56.2 kg plus 1.41 kg per inch. For women, 53.1 kg plus 1.36 kg per inch. It has the highest starting point and the gentlest slope, so it's usually the most generous for shorter people and the lowest for the tall.

Hamwi (1964)

Hamwi works in pounds. Men get 106 lb plus 6 lb per inch over 5 feet, and women get 100 lb plus 5 lb per inch. We convert the result to kilograms for you. It tends to give the highest figure for tall men.

Look at the 5 ft 0 in woman. Her estimates run from 45.4 kg to 53.1 kg, a gap of nearly 8 kg. That's why we show all four and don't crown a winner.

The healthy BMI range, as a fifth view

We add one more line: the weights that would put you inside a healthy BMI range at your height. With the WHO scale that's a BMI of 18.5 to 24.9. With the South Asian cut-offs it's 18.5 to 22.9. It's a range from the start, which makes it a good companion to the single-number formulas.

A worked example

Let's run the numbers for the woman from the start of this guide. She's 165 cm tall, medium frame, and we'll use the standard WHO range.

Metric version

First convert her height to inches: 165 divided by 2.54 is 64.96 inches. That's 4.96 inches over 5 feet (60 inches). Now apply each formula for women.

1. Devine: 45.5 + 2.3 × 4.96 = 56.9 kg
2. Robinson: 49 + 1.7 × 4.96 = 57.4 kg
3. Miller: 53.1 + 1.36 × 4.96 = 59.8 kg
4. Hamwi: (100 + 5 × 4.96) lb = 124.8 lb, which is 56.6 kg

The BMI route: her height in metres squared is 1.65 × 1.65 = 2.7225. Multiply by 18.5 to get 50.4 kg, and by 24.9 to get 67.8 kg. So the WHO healthy range for her is 50.4 to 67.8 kg.

Imperial version

Say she measures herself as 5 ft 5 in, which is 65 inches. That's 5 inches over 5 feet.

1. Devine: 45.5 kg + 2.3 × 5 = 57.0 kg, or about 125.7 lb
2. Robinson: 49 + 1.7 × 5 = 57.5 kg, or about 126.8 lb
3. Miller: 53.1 + 1.36 × 5 = 59.9 kg, or about 132.1 lb
4. Hamwi: 100 lb + 5 × 5 = 125 lb, which is 56.7 kg

The two versions differ by a tenth of a kilo here and there, only because 5 ft 5 in is 165.1 cm and not exactly 165.

Putting it together

The four formulas land between about 56.6 and 59.8 kg. We pad that by 2 kg on each side, because no formula is that precise, and keep the result inside her BMI range. That gives a reasonable range of roughly 54.6 to 61.8 kg (about 120 to 136 lb). At 66 kg she's a little above that range, and still well inside the WHO healthy BMI range. Both statements are true at once, and that's the point. The range is a guide, not a grade.

Where these formulas came from

Here's the part most calculator pages skip. Devine's formula first appeared in a 1974 paper on dosing an antibiotic, gentamicin. Doctors needed a quick way to estimate a patient's lean size so they could work out a safe dose. It wasn't designed to tell anyone what to aim for on the scales, and its own roots are a little murky. Robinson and Miller published their versions in 1983 in the same pharmacy world, tweaking the numbers to fit drug-dosing needs.

Hamwi is older, from 1964. It began as a rule of thumb for dietitians working with people who had diabetes, so it was a practical shortcut and not a research finding. Before all of these, insurance companies published "desirable weight" tables based on who lived longest in their customer records. Those tables shaped how people thought about ideal weight for decades.

None of this makes the formulas useless. It just means they're rough tools that got borrowed for a job they weren't built for. Treat them like a rule of thumb for cooking, not a prescription.

Why your ideal weight can differ

Frame size

Two women can both be 165 cm and have very different bone structure. Someone with fine wrists and narrow shoulders will often be comfortable at a lower weight than someone with a broad frame. That's why the calculator has a frame setting, which adjusts the formula results by about 10% either way. The wrist helper gives you a quick guess if you're not sure which one you are.

Muscle

Take a 28-year-old man who lifts weights four times a week. He's 178 cm and 84 kg, and his body fat is low. The formulas say around 70 to 75 kg, and a plain BMI chart calls him overweight. He isn't. Muscle is dense and heavy, and none of these tools can tell muscle from fat.

Age

The formulas don't change with age, but real bodies do. Many people carry a bit more weight as they get older, and some research suggests a slightly higher weight can be protective later in life. A 55-year-old with a smaller frame might feel best at the lower end of the range, and that's perfectly reasonable too.

Ethnicity and where fat sits

The WHO healthy BMI range of 18.5 to 24.9 came mostly from studies of European populations. Research on people of South and East Asian background found that health risks like type 2 diabetes begin to rise at lower BMI values. If your doctor has talked about a different cut-off for people of South or East Asian background, that's why. Our Asian setting uses 22.9 as the upper end of the healthy range. It's a screening cut-off, not a diagnosis, and a lot of people in the region are healthy above it. It's just a more careful line.

Ideal weight vs healthy BMI range vs body fat %

These three ideas get mixed up all the time. Ideal weight, as the formulas calculate it, is a single estimate from your height and sex. The healthy BMI range is a band of weights for your height, built from a ratio of weight to height squared. Body fat percentage measures how much of your weight is fat, which is what you actually care about for health.

Body fat is the most informative of the three but also the hardest to measure well at home. Smart scales are rough. Skinfold calipers need practice. DEXA scans are accurate but not something you'd do weekly. If you want a simple, free extra check, measure your waist and divide it by your height. A result under 0.5 is a common rule of thumb. Our BMI Calculator includes that ratio, and the BMR Calculator helps if you're curious how many calories your body uses at rest.

If you want to compare your numbers across measurement systems, the unit converter handles kilograms and pounds, and feet and inches, and you can check your age in exact years and months with the Age & Date Calculator.

What to do with your result

If you're inside the range

Good news. Nothing needs fixing. Keep eating in a way you can live with, stay active, sleep properly, and don't chase a lower number just because it's lower.

If you're above it

A bigger number on the scale doesn't mean something's wrong, and there's no deadline. If you'd like to move closer to the range, small steady changes beat big dramatic ones. A pace of about 0.25 to 0.5 kg a week (roughly half a pound to a pound) is realistic for most people and easy to keep going. That works out to about a kilo or two a month. Crash diets and skipping meals tend to backfire, because the weight comes back and you feel awful on the way.

If you're below it

Some people are naturally slim and healthy. If that's you, and you eat well and feel strong, you probably don't need to change anything. If you've lost weight without trying, feel tired a lot, or your periods have stopped, it's worth a conversation with a doctor. To gain weight steadily, the same 0.25 to 0.5 kg a week is a sensible pace, with regular meals, enough protein and some strength training.

When to see a professional

Talk to a doctor or registered dietitian if you have a medical condition, take medication, are pregnant, have a history of disordered eating, or feel anxious about food and weight. They can look at the whole picture, which no calculator can.

Common myths and mistakes

Myth: there's one correct number for me. There isn't. There's a range, and the spread between formulas is part of the answer.

Myth: being outside the range means I'm unhealthy. Health depends on blood pressure, blood sugar, fitness, sleep, and more. Weight is only one input.

Myth: lower is always better. Being underweight carries its own risks, including weak bones, low energy, and a weaker immune system.

Mistake: comparing yourself with a chart made for someone else. A chart built on one population or one decade can mislead people elsewhere. If you're from South Asia, use the Asian range and talk to a local doctor about what suits you.

Mistake: weighing yourself every day and reacting to it. Weight moves by a kilo or two over a day through water, food and salt. Weekly checks at the same time of day tell you much more.

Special cases

Older adults. After about 65, a slightly higher weight can be fine, and unplanned weight loss can be a bigger worry than a few extra kilos. Treat the range as a loose guide and ask your doctor.

Athletes and very muscular people. Formulas will usually undershoot. Body composition and performance matter more than the scale.

Pregnancy. These formulas don't apply. Healthy weight gain in pregnancy depends on your starting weight, so follow your midwife or doctor's advice.

Teenagers and children. Adult formulas don't work for growing bodies, so the calculator won't show adult targets under 18. Doctors use growth charts and BMI-for-age percentiles, and a paediatrician or school nurse can explain them.

Frequently asked questions

Medical disclaimer

The results and information on this page are for general education only. They are estimates, not medical advice, a diagnosis or a treatment plan. Ideal weight formulas can't account for muscle mass, frame, age, ethnicity or health conditions. Please talk to a doctor or registered dietitian before making changes to your diet or exercise, especially if you're pregnant, have a medical condition, or have a history of disordered eating.