Ideal Weight Calculator — What Should You Actually Weigh?

What “Ideal Weight” Really Means

Right, first things first. The phrase “ideal weight” does a lot of damage. It makes it sound like there’s one perfect number with your name on it, and being off it means you’ve failed somehow. Rubbish. That’s just not the deal.

Ideal body weight — IBW, if you like acronyms — is a reference point and nothing grander. A ballpark figure for your height and sex, pulled from population data collected over the decades. It points you toward where a healthy weight usually lands for someone shaped like you. And I’d underline that word “usually,” because it’s doing a lot of quiet work.

Now here’s the kicker most folk have no idea about. Nobody invented these formulas to help you diet. The most famous one? A doctor came up with it to work out drug doses. Certain medicines get measured against lean body mass, so physicians wanted a fast way to guess that from height. The whole “this is your target weight” thing came later, bolted on by the rest of us. Bear that in mind when you read your number — it’s a signpost, not a sentence.

The Formulas Behind Your Number

One formula would’ve been the lazy way. The calculator runs three instead, and shows you all of them, because not one of them holds the full truth on its own. Quick rundown of who’s who.

Hamwi (1964). Granddad of the lot. Dr Hamwi knocked it together as a bedside reference for nutrition. The per-inch jump for men is the steepest here, so tall blokes tend to come out heaviest on this one.

Devine (1974). This is the one you’ll meet everywhere — still lurking inside half the hospital software out there. And get this: it began life as a drug-dosing trick before it ever became a weight benchmark. Bit of an accidental celebrity.

Robinson (1983). Basically Devine, tidied up with fresher insurance figures. It tends to land in the middle of the pack. Which is handy, honestly — having a moderate one next to the other two stops any single answer running away with things.

What ties them together is the shape. Each one starts with a base weight for a five-foot person, then tacks on a fixed bit for every inch above that. Why do they disagree? Different data, different decade, different gut feeling about what “healthy” looks like. And that disagreement isn’t a fault. It’s the whole reason we show you three — together they give you a range, and a range is honest in a way a single smug number never is.

Why We Show You a Range, Not One Number

Used other calculators that fire back one tidy figure? This’ll feel odd, then. But that’s a good thing. That one number was always fibbing to you a bit.

Have a think. Feed the formulas a bloke who’s 178 cm and they’ll spit out anything from roughly 70 to 75 kg, depending which one’s talking. Five kilos between them. And every last one of those numbers is “right” by its own maths. So go on — which is the real one? All of them. None of them. Honest answer: it’s somewhere in that gap.

Which is exactly why the tool also lobs in a healthy BMI range for your height on top. And brace yourself, because that window’s even bigger — for someone 170 cm tall it runs across the best part of 19 kilos. Nineteen. Every pound of it healthy. If that doesn’t cure you of fixating on one exact number on the scales, nothing will.

The Body Frame Bit

You’ll have clocked the body frame dropdown. Worth a minute, because people wave it away and they shouldn’t.

Picture two people, same height, same sex, built like chalk and cheese — one all fine narrow bones, the other broad with a heavy skeleton. Telling them to weigh the same is daft on the face of it. The broad one starts heavier before a scrap of fat enters the picture, because the frame itself simply weighs more.

So the calculator tweaks for it: small frames come down about 10%, big frames go up the same. No clue which you are? Easy test. Curl your fingers round the opposite wrist. Thumb and middle finger overlap with room to spare — small frame. Just kissing — medium. Can’t even get them to meet — large. It’s hardly lab science, but it’ll sort you out well enough.

How to Actually Use Your Result

Got your range in front of you? Here’s how to read it without losing the plot.

Sitting inside the range? Lovely. You’re in healthy territory, job done. Don’t go chasing the bottom number just because it’s there. Where you feel strong and full of beans inside that band beats the precise digit every time.

Above it? Don’t spiral, and for heaven’s sake don’t crash-diet. Lift weights or carry a decent bit of muscle? You might sit over “ideal” and be perfectly fit — muscle’s heavier than fat, never forget that. If it really is fat you’re after losing, slow wins the day. Sort your calories on our TDEE Calculator and slide into a gentle deficit.

Below it? Have a think. Underweight brings its own baggage — brittle bones, a dodgy immune system, running on empty. If you didn’t mean to get there, that’s a decent reason to have a word with your doctor.

And here’s the one that trips everyone up: this number tells you nothing about what you’re made of. You could nail your “ideal weight” to the gram and still be soft — too much fat, not enough muscle. Want the real story underneath? Run it alongside our BMI Calculator as a quick second opinion.

Where These Formulas Fall Down

It’d be a bit dishonest of me to dress these up as flawless. They’ve got proper blind spots, and spotting them stops you treating the result like gospel.

Muscle versus fat? Haven’t a clue. Same gap BMI has. A muscly athlete sails clean past their “ideal” while looking lean as you like, because height’s all the formula knows — what you’re actually built of is invisible to it.

Then there’s the age of the thing. These come off decades-old insurance tables and a narrow slice of people. They make no room for the sheer range of human builds, and they certainly don’t bend for ethnic differences in body composition.

Oh, and age — your age. What’s a fair weight at 25 won’t necessarily be at 65. Bodies shift, muscle comes and goes, and a single fixed formula is blind to all of it.

None of that bins them, mind. Far from it. Just take the answer as a ballpark — a jumping-off point for thinking about your weight, not some precise figure to flog yourself against.

Frequently Asked Questions