If you’ve ever wondered how to calculate ideal weight, here’s a small surprise waiting for you: type your height into four of the classic formulas and you’ll get four different answers. A 5’10” man gets told he’s “ideal” anywhere between 70 and 75 kilograms. Same man, same height, four textbooks — and a 5-kilo spread. So which number do you actually use?
None of them, exactly. And all of them, a little.
This guide walks you through how to calculate ideal weight the honest way: the four classic formulas (Hamwi, Devine, Robinson and Miller), the healthy BMI range that doctors actually screen against, the frame-size tweak that most calculators skip, and fully worked examples so you can check every number yourself. By the end you’ll have a range you can trust — not a single magic number that doesn’t exist.
Table of Contents
Why One Height Gives You Four Different “Ideal” Weights
Before we do any maths, it helps to know where these formulas came from — because it explains why they disagree with each other.
The oldest is the Hamwi formula, published in 1964 by Dr G.J. Hamwi for the American Diabetes Association. It was never meant to tell people what they should weigh. It was a quick clinical reference for estimating the caloric needs of people with diabetes — 106 pounds for the first five feet plus 6 pounds per inch (for men), in round imperial numbers a busy clinician could compute in their head.
A decade later, Dr B.J. Devine published his formula in 1974 — in a pharmacy journal, for drug dosing. Doctors needed a way to estimate a patient’s lean body mass so they could dose certain antibiotics safely, and Devine’s equation became the standard for that job. It is still used in hospitals today, which is why many online calculators default to it. But it was designed to keep medication doses safe, not to set your personal weight goal.
Then came two 1983 revisions. Dr J.D. Robinson recalibrated Devine’s formula against newer population data, and Dr D.R. Miller published his own revision the same year. Both kept the same shape — a base weight at five feet, plus a per-inch increment — but fitted the numbers to updated height-weight statistics.
That’s the real story behind how to calculate ideal weight: four formulas, built in different decades, for different jobs, from different data. None of them knows your muscle mass, your frame, or your health history. They’re all estimates — useful ones, but estimates.
How to Calculate Ideal Weight: The Four Formulas
Every one of the four formulas follows the same shape:
Ideal body weight (kg) = base + per-inch × (height in inches − 60)
The 60 is five feet in inches. So (height − 60) is simply how many inches you stand above five feet. Memorise this shape and you’ve learned how to calculate ideal weight the way every online calculator does it — they all run these same four lines under the hood. Here are the numbers, verified against standard medical references:
| Formula | Men | Women |
|---|---|---|
| Hamwi (1964) | 48 + 2.7 per inch over 5 ft | 45.5 + 2.2 per inch over 5 ft |
| Devine (1974) | 50 + 2.3 per inch over 5 ft | 45.5 + 2.3 per inch over 5 ft |
| Robinson (1983) | 52 + 1.9 per inch over 5 ft | 49 + 1.7 per inch over 5 ft |
| Miller (1983) | 56.2 + 1.41 per inch over 5 ft | 53.1 + 1.36 per inch over 5 ft |
All four give results in kilograms. Notice the pattern: Hamwi adds the most per inch (2.7 kg for men), Miller the least (1.41 kg). That’s why the four agree closely near five feet and drift apart the taller you get — at six feet, Hamwi and Miller can differ by more than 7 kg for the same man.
A few practical notes:
- Under 5 feet tall? Subtract the same per-inch amount for every inch below 60. The formulas extend downward symmetrically — so at 59 inches you’d subtract one per-inch increment from the base.
- Keep your units straight. These formulas want inches in and give kilograms out. If you think in centimetres, divide by 2.54 first (there’s a worked conversion below).
- Don’t average them into a single “true” number — or rather, do, but treat the average as a rough centre, not a verdict. The honest answer is the range.
Worked Example 1: Man, 5’10”
Let’s make this concrete. Meet our example: a man, 5 feet 10 inches. Step by step:
Step 1 — Convert to inches. 5’10” = (5 × 12) + 10 = 70 inches.
Step 2 — Inches over five feet. 70 − 60 = 10 inches over.
Step 3 — Run each formula:
- Devine: 50 + 2.3 × 10 = 50 + 23 = 73.0 kg
- Robinson: 52 + 1.9 × 10 = 52 + 19 = 71.0 kg
- Miller: 56.2 + 1.41 × 10 = 56.2 + 14.1 = 70.3 kg
- Hamwi: 48 + 2.7 × 10 = 48 + 27 = 75.0 kg
| Formula | Ideal weight |
|---|---|
| Devine (1974) | 73.0 kg (161 lb) |
| Robinson (1983) | 71.0 kg (157 lb) |
| Miller (1983) | 70.3 kg (155 lb) |
| Hamwi (1964) | 75.0 kg (165 lb) |
| Span across formulas | 70.3–75.0 kg |
So one height, four answers: anywhere from 70.3 to 75.0 kg (about 155–165 lb). Do the arithmetic once by hand and you’ll never wonder how to calculate ideal weight again — the method is always the same: convert to inches, subtract 60, multiply, add.
Worked Example 2: Woman, 5’4″
Same method, different person: a woman, 5 feet 4 inches.
Step 1 — Convert. 5’4″ = (5 × 12) + 4 = 64 inches.
Step 2 — Inches over five feet. 64 − 60 = 4.
- Devine: 45.5 + 2.3 × 4 = 45.5 + 9.2 = 54.7 kg
- Robinson: 49 + 1.7 × 4 = 49 + 6.8 = 55.8 kg
- Miller: 53.1 + 1.36 × 4 = 53.1 + 5.44 = 58.5 kg
- Hamwi: 45.5 + 2.2 × 4 = 45.5 + 8.8 = 54.3 kg
| Formula | Ideal weight |
|---|---|
| Devine (1974) | 54.7 kg (121 lb) |
| Robinson (1983) | 55.8 kg (123 lb) |
| Miller (1983) | 58.5 kg (129 lb) |
| Hamwi (1964) | 54.3 kg (120 lb) |
| Span across formulas | 54.3–58.5 kg |
Again, a four-kilo spread for the same woman. Notice something interesting too: near five feet the four formulas nearly agree (they differ by less than 5 kg here), while for our taller 5’10” man they fanned out more. That’s the per-inch slope at work — the taller you are, the wider the disagreement.
How to Calculate Ideal Weight From Your BMI (the Wider Range)
The four formulas give you a span. But most doctors don’t start from Hamwi or Devine — they start from BMI, body mass index:
BMI = weight (kg) ÷ height (m)²
The CDC classifies adult BMI into bands, and the healthy-weight band is 18.5–24.9 for adults. (You can see the official categories on the CDC’s adult BMI categories page.) Turn that around and you get a healthy weight range for any height:
Healthy weight range = 18.5 × height² to 24.9 × height² (height in metres)
Let’s apply it to our two examples.
Example 1 — the 5’10” man (1.778 m): height² = 3.1613. Lower bound: 18.5 × 3.1613 = 58.5 kg. Upper bound: 24.9 × 3.1613 = 78.7 kg. Healthy BMI weight range: 58.5–78.7 kg.
Example 2 — the 5’4″ woman (1.6256 m): height² = 2.6426. Lower bound: 18.5 × 2.6426 = 48.9 kg. Upper bound: 24.9 × 2.6426 = 65.8 kg. Healthy BMI weight range: 48.9–65.8 kg.
Look at those bands. For the man, the four formulas said 70.3–75.0 kg; the BMI band says 58.5–78.7 kg — much wider. That’s not a contradiction. The BMI band is a population screening range (who falls where across millions of people), while each formula is a single-line estimate. That combination — the formula span plus the BMI band — is the complete answer to how to calculate ideal weight instead of just guessing it. The formulas sit roughly in the middle of the band, and for most people the two methods point to the same neighbourhood.
Use the formula span as your personal estimate and the BMI band as your guardrails. If the formulas’ numbers land inside your healthy BMI range, you can be confident they’re sensible. If they fall outside it — rare, but it happens at extreme heights — trust the band, not the formula.
Adjusting for Frame Size
Here’s the tweak most one-click calculators skip: bone structure. Two people at the same height can legitimately carry different weights if one has a small frame and the other a large one — broader shoulders and thicker wrists weigh something.
The standard adjustment, and the one built into our ideal weight calculator, is ±10%: take the medium-frame result and subtract 10% for a small frame, add 10% for a large frame. It’s the step most guides on how to calculate ideal weight leave out — and it’s the one that matters most if your bones run small or large.
Example 3 — back to our 5’10” man. His Robinson result was 71.0 kg (the medium-frame figure):
- Small frame: 71.0 × 0.90 = 63.9 kg
- Medium frame: 71.0 kg
- Large frame: 71.0 × 1.10 = 78.1 kg
How do you know your frame? The classic quick test is the elbow-breadth method: wrap the thumb and middle finger of one hand around the wrist of the other. If they overlap, your frame runs small; if they just meet, medium; if they don’t meet, large. Our ideal weight calculator walks you through the elbow-breadth check and applies all four formulas at once, so you don’t have to do this arithmetic by hand.
If You Think in Centimetres
Everything above needs inches. If your tape measure speaks metric, divide centimetres by 2.54 first, then proceed as normal.
Example 4 — a woman, 165 cm:
Step 1 — Convert to inches. 165 ÷ 2.54 = 64.96 inches (about 5’5″).
Step 2 — Inches over five feet. 64.96 − 60 = 4.96.
Step 3 — Apply Devine: 45.5 + 2.3 × 4.96 = 45.5 + 11.41 = 56.9 kg.
For quick reference, here are the Devine results across common heights — handy if you want to eyeball your number before running the full set of four:
| Height | Devine — Men | Devine — Women |
|---|---|---|
| 150 cm | 47.8 kg | 43.3 kg |
| 155 cm | 52.4 kg | 47.9 kg |
| 160 cm | 56.9 kg | 52.4 kg |
| 165 cm | 61.4 kg | 56.9 kg |
| 170 cm | 65.9 kg | 61.4 kg |
| 175 cm | 70.5 kg | 66.0 kg |
| 180 cm | 75.0 kg | 70.5 kg |
| 185 cm | 79.5 kg | 75.0 kg |
| 190 cm | 84.0 kg | 79.5 kg |
Remember, this is one formula of four — run your height through the full ideal weight calculator to see the complete picture with the BMI band and frame-size adjustment included.
5 Common Mistakes When Calculating Ideal Weight
- Treating one formula’s number as a target. Picking “Devine says 73, so I must be 73.0” misses the entire point. The formulas are estimates from old datasets; the range is the answer, not the digits.
- Forgetting that muscle breaks all four. None of these formulas knows whether you lift weights. A muscular person can sit above every formula’s number while being leaner and healthier than someone sitting “in range” — this is the same reason athletes can read as “overweight” on BMI. If you train seriously, your body fat percentage calculator is the metric that actually matters.
- Mixing units mid-calculation. Feet aren’t decimal (5’10” is not 5.10 anything), pounds aren’t kilograms, and the formulas want inches in. Convert first, calculate second — every time.
- Ignoring frame size. A 10% swing on a 71 kg result is 7 kg — larger than the gap between some of the formulas themselves. If you’ve never adjusted for frame, you’ve been comparing yourself to a number that wasn’t even aimed at you.
- Chasing the number instead of the range. Your weight will bounce a kilo or two with hydration, meals, and the time of day. A range absorbs that noise. A single target number turns normal fluctuation into a bad mood.
Frequently Asked Questions
Which ideal weight formula is most accurate?
None is definitively “most accurate” — they were built for different jobs. Devine (1974) is the most widely used in clinical settings because it was designed for drug dosing, so many calculators default to it. Robinson and Miller (1983) were fitted to more recent population data and tend to sit closer to modern averages. Hamwi (1964) gives the highest numbers for tall people. The most honest approach is to compute all four and work with the range they give you.
Why do the four formulas give different numbers?
Because they were derived from different datasets in different decades for different purposes — Hamwi for diabetes care (1964), Devine for drug dosing (1974), and Robinson and Miller as 1983 recalibrations of population data. They differ mainly in how much weight they add per inch of height: Hamwi adds 2.7 kg per inch for men, Miller only 1.41 kg, so the taller you are, the further apart their answers drift.
What if I’m under 5 feet tall?
The formulas extend downward: subtract the same per-inch amount for every inch below 60 inches (5 feet). For example, a man at 59 inches would use Devine as 50 − 2.3 × 1 = 47.7 kg. That said, treat results at the extremes of height with extra caution — all four formulas were derived from typical adult height ranges and become less reliable for very short or very tall people.
I’m muscular — do these formulas work for me?
Not well. Like BMI, the four formulas only know your height (and sex) — they can’t tell muscle from fat. A muscular person will typically land above the formula range while having low body fat and good metabolic health. If you strength-train regularly, track your body fat percentage alongside or instead of these formulas — our body fat percentage calculator and guide to how to calculate body fat percentage walk through that.
Ideal weight vs healthy BMI range — which should I use?
Use both, for different purposes. The four formulas give you a personalised estimate anchored to your height and sex; the healthy BMI range (18.5–24.9) gives you wider population guardrails, as used by the CDC’s adult BMI categories. If the formulas’ span sits inside your BMI band, you’re in solid territory. If they disagree sharply, the BMI band is the safer anchor.
How does frame size change my ideal weight?
By about ±10%. Take the medium-frame result from any formula and subtract 10% for a small frame or add 10% for a large frame — so a 71.0 kg result becomes 63.9 kg on a small frame and 78.1 kg on a large one. The quickest self-check is the elbow-breadth method: wrap your thumb and middle finger around your opposite wrist — overlap means a small frame, just touching means medium, a gap means large.
Learning how to calculate ideal weight is worth doing by hand exactly once — now you know where every number comes from and, more importantly, why no single number deserves to be called “the” answer. After that, let the tools do the arithmetic: run your height, sex and frame through our ideal weight calculator to get all four formulas plus your healthy BMI range in one go.
And if you’re working toward that range, two companion numbers matter more than the ideal-weight figures themselves: your daily calorie needs, which decide whether you gain, lose or hold weight, and your body fat percentage, which tells you what your weight is actually made of. The formulas in this guide point you at the target; those two tell you how to move toward it honestly.