How to Calculate Your Ideal Weight (And Why There's No Single Number)

Google "ideal weight" and you'll get about twelve different answers, none of which agree with each other. One chart says you should weigh 155 pounds. Another says 172. A third insists 140 is the "perfect" number. They all sound confident, and they all can't be right.

The truth is that "ideal weight" depends on a lot more than a simple chart. Your body frame, muscle mass, bone density, age, and even your fitness level all play a role. In this guide, I'll walk you through the four main formulas people use, show you how they differ, and explain what actually matters when you're trying to figure out a healthy target weight.

The four main ideal weight formulas

Most online ideal weight calculators are running one of four equations behind the scenes. Each was developed by a different researcher, at a different time, for a slightly different purpose. Here they are, applied to two real examples: a 5'10" male and a 5'5" female.

Devine Formula (1974)

Created by Dr. B.J. Devine, originally designed for calculating medicinal dosages. Despite its clinical origin, it became the most widely used ideal weight formula in the United States.

• Males: 50 kg + 2.3 kg per inch over 5 feet
• Females: 45.5 kg + 2.3 kg per inch over 5 feet

Robinson Formula (1983)

Dr. J.D. Robinson modified Devine's formula after observing that it tended to overestimate ideal weight for shorter people. He lowered the base weights slightly.

• Males: 52 kg + 1.9 kg per inch over 5 feet
• Females: 49 kg + 1.7 kg per inch over 5 feet

Miller Formula (1983)

Also published in 1983, Dr. G.J. Miller's formula is similar to Robinson's but uses a lower base weight and slightly different incremental additions. It tends to give the most conservative (lowest) estimates.

• Males: 56.2 kg + 1.41 kg per inch over 5 feet
• Females: 53.1 kg + 1.36 kg per inch over 5 feet

Hamwi Formula (1964)

Dr. G.J. Hamwi developed this formula for clinical weight-loss programs. It tends to give the highest estimates and allows for a wider "ideal" range.

• Males: 48 kg + 2.7 kg per inch over 5 feet
• Females: 45.5 kg + 2.2 kg per inch over 5 feet

Look at how much they disagree

For our 5'10" male, the formulas range from 155.0 lbs (Miller) to 165.3 lbs (Hamwi) — a spread of over 10 pounds. For the 5'5" female, it's 124.6 lbs (Hamwi) to 132.1 lbs (Miller) — more than 7 pounds apart. That's a meaningful difference if you're trying to hit a specific target.

None of these formulas is "wrong," exactly. They're just built on different assumptions from different datasets. The problem starts when people treat any single one of them as gospel.

The BMI-based approach: a range, not a number

A more flexible approach uses the healthy BMI range (18.5 to 24.9) and works backward from your height to find a weight window. This gives you a range of 20-30 pounds, which is honestly more realistic than trying to land on a single number.

The formula is straightforward:

For our 5'10" male (1.78 m):

For our 5'5" female (1.65 m):

Now all four formula results fall comfortably within this range. That's reassuring. But notice how wide the range is — 45 pounds for the man, 38 pounds for the woman. Saying "your ideal weight is 155 lbs" is like saying "your ideal house temperature is 71.3 degrees." Technically within the range, but the specificity is fake.

Why formulas don't tell the whole story

All four formulas, plus the BMI approach, share the same fundamental flaw: they only use height and gender. Real bodies vary in ways that two measurements can't capture.

Muscle mass

This is the single biggest factor that formulas miss. Muscle is roughly 18% denser than fat. Two people who look identical in the mirror can weigh very differently on a scale if one strength trains and the other does not. A 5'10" man who weighs 185 lbs with 15% body fat is in far better shape than one who weighs 165 lbs with 28% body fat — but most "ideal weight" charts would label the first person as overweight.

Think about professional athletes. LeBron James, at 6'9" and roughly 250 lbs, has a BMI of about 26.5 — technically "overweight." Usain Bolt, at 6'5" and 207 lbs, has a BMI of about 24.5 — just barely in the "normal" range. Neither of these men is carrying excess fat.

Bone density and frame size

People with larger frames literally have bigger, heavier skeletons. The difference between a small-boned person and a large-boned person of the same height can be 8-10 pounds of bone alone. The Hamwi formula attempts to account for this by adding 10% for large frames and subtracting 10% for small frames, but most calculators don't even ask about frame size.

Age

As people age, they naturally lose muscle mass (a process called sarcopenia) and may gain body fat even at the same weight. This means an older adult at the "ideal" weight for their height might actually have a higher body fat percentage than a younger adult at the same weight. Some research suggests that a slightly higher BMI (25-27) may actually be protective for adults over 65, because it provides a buffer against unintentional weight loss during illness.

Fitness level and body composition

A person who runs 20 miles a week and a person who is sedentary can have the exact same height and weight but vastly different cardiovascular health, insulin sensitivity, and longevity prospects. Weight alone tells you nothing about fitness.

A better approach to finding your target weight

Instead of chasing a single number from a formula, consider these more meaningful metrics:

• Body fat percentage.This is what people actually care about when they talk about "ideal weight." For men, 10-22% is generally considered healthy; for women, 20-32%. You can estimate this at home with a body fat calculator using tape measurements, or get it measured professionally with a DEXA scan.
• Waist-to-hip ratio. This tells you where you carry your fat, which matters a lot more than how much you carry. Fat stored around the midsection (visceral fat) is strongly linked to heart disease and diabetes. Above 0.90 for men or 0.85 for women is considered elevated risk.
• How you feel day to day.Energy levels, sleep quality, joint health, and mood are practical indicators that no formula can measure. If you're active, sleeping well, and feel good, your weight is probably in a reasonable place — regardless of what any chart says.
• Blood markers. Blood pressure, fasting glucose, triglycerides, and HDL/LDL cholesterol give you objective data about your metabolic health. These are far more predictive of long-term health outcomes than any weight measurement.

Frequently Asked Questions

What's the most accurate ideal weight formula?

None of the major formulas (Devine, Robinson, Miller, Hamwi) is definitively "most accurate" because they all use height and gender as their only inputs. For a quick estimate, Devine is the most widely cited. For a more useful number, look at the BMI-based healthy weight range for your height, which gives you a 20-30 pound window instead of a single target.

Why do different calculators give different results?

Each formula was developed by different researchers using different study populations and different assumptions. Devine (1974) was based on medicinal dosage calculations. Robinson (1983) and Miller (1983) were adjustments to Devine. Hamwi (1964) was designed for clinical weight-loss settings. They can disagree by 15 pounds or more for the same person.

Is BMI outdated?

BMI is a useful screening tool at the population level, but it has known limitations for individuals. It cannot distinguish between fat mass and lean mass, which means muscular people are often classified as "overweight" or "obese." It also does not account for age, sex, ethnicity, or fat distribution. Most health professionals recommend using BMI as one data point among many, not as a standalone health judgment.

How much does muscle affect ideal weight?

Muscle is about 18% denser than fat, so someone who is muscular will weigh more than someone of the same size who is not. A competitive bodybuilder can easily weigh 20-40 pounds more than a "normal BMI" weight and still be at a healthy body fat percentage. If you strength train regularly, you should expect to weigh more than standard formulas suggest.

Should I aim for the middle of my healthy weight range?

Not necessarily. The healthy BMI range (18.5 to 24.9) translates to roughly a 20-30 pound window for most adults. Where you naturally fall within that range depends on your frame size, muscle mass, age, and genetics. Many health professionals suggest aiming for the lower end if you have other risk factors (like high blood pressure) and the middle-to-upper end if you are very active.

Related Calculators

• Ideal Weight Calculator — Compare four formulas side by side
• BMI Calculator — Calculate your Body Mass Index
• Body Fat Calculator — Estimate your body fat percentage
• Calorie Calculator — Plan your daily calorie intake

Want to see what all four formulas say about your weight? Try our ideal weight calculator — it runs all four equations at once so you can see the full range in one place.