Ideal Weight Calculator

What should you weigh?

Enter your height and the tool gives you the healthy weight range for it, along with where your current weight sits relative to that range. Below, the four classic “ideal weight” formulas are shown side by side.

They are shown together rather than as a single headline number, and that is the point of the page. Read on for why.

Everything runs in your browser. Nothing here is medical advice.

There is no single ideal weight

This tool is called an ideal weight calculator because that is what people search for. The honest answer to the question is a range, and a fairly wide one.

Health outcomes do not turn on a single value. They spread across a band — for a person of 175 cm, roughly 57 to 76 kg — and within that band, other things matter far more than where exactly you sit: how much muscle you carry, where fat is distributed, how fit you are, what you eat, whether you sleep.

Any tool that answers “your ideal weight is 70.5 kg” is presenting a precision that nothing in the evidence supports.

Where the formulas actually came from

This is worth knowing, because it changes how much weight to put on them.

The four formulas were built for clinical drug dosing, not for telling anyone what to weigh.

Some drugs are dosed on body weight, but the relevant quantity is closer to lean mass than to total weight — dosing a heavier patient on their actual weight can overdose them. Clinicians needed a quick estimate of “what would this person weigh at an average build for their height”, and that is what these formulas are.

Devine (1974) is the most-copied. It appeared in a one-page note about gentamicin dosing, and its author later acknowledged the numbers had no study behind them — they were a convenient rule.

Robinson (1983) and Miller (1983) are refits of Devine against measured population data. Miller’s gentler slope makes it the most forgiving at tall heights.

Hamwi (1964) is the oldest, from a diabetes-management ruleset, and the steepest.

All four share the same shape: a base weight at five feet, plus a fixed amount per inch above it. None accounts for build, muscle, age, or anything else.

Their disagreement is the useful part

For a man of 180 cm the four give answers spanning several kilograms. For the same person. Using the same two inputs.

That spread is not a flaw to be averaged away — it is the most informative thing on the page. Four reasonable people looking at the same question produced four different answers, which tells you the question does not have the precise answer its phrasing implies.

This is why the tool shows all four rather than picking one. Picking one would produce a cleaner-looking result and a less truthful one.

The range in the header is the number to use

It comes from BMI: the weights that put you between 18.5 and 24.9, the band conventionally called healthy for adults.

Unlike the four formulas, this one is grounded in health outcomes — it comes from studying what happens to large populations at different weights, not from what dose of an antibiotic to give someone. It is the only figure here with that behind it.

It is still a population measure, with the limits that implies. Read the next section before treating it as a verdict.

What BMI cannot see

BMI knows two things: your height and your weight. It cannot tell muscle from fat, and it does not know where the fat is.

The consequences are real. A lean, muscular person can be classified overweight while being in excellent health — this is routine for athletes. Someone within the healthy range can carry a lot of fat and very little muscle, which is a genuine health risk that BMI cannot see at all. Fat around the abdomen carries more risk than the same amount elsewhere, and BMI is blind to distribution.

The thresholds also vary by population. People of South Asian descent, for instance, show elevated risk at lower BMI values, and several health bodies use lower cut-offs accordingly.

Two measurements that add a lot for very little effort: waist circumference (risk rises above about 94 cm for men and 80 cm for women), and waist-to-height ratio, where keeping your waist under half your height is a simple and surprisingly robust guide.

If you are under five feet

The tool will warn you, and the reason is specific.

Every formula is defined as “X kilograms, plus Y per inch over five feet”. None of them says what happens below that. Extending the line downwards is the usual practice and is what this tool does, but it is extrapolation past the edge of the definition, so it is flagged rather than presented with the same confidence.

The BMI-based range in the header has no such problem — it is defined at any height.

A better question

“What should I weigh” is a harder question to answer usefully than it looks, and it is often not the question worth asking.

Weight is one number standing in for several things that matter more: body composition, fitness, blood pressure, blood lipids, blood sugar, sleep, and how you actually feel. It is easy to measure, which is why it dominates — not because it is the most informative.

If you are trying to work out whether your weight is a health concern, that is a conversation with a doctor who can see the rest of the picture. A formula from 1974 designed for antibiotic dosing is not the right instrument, and neither is a number on a page that has never met you.

Frequently asked questions

Why does it show a range instead of one number?

Because the honest answer is a range. Health outcomes do not turn on a single value — they spread across a band several kilograms wide. Any tool giving you one number to the decimal place is presenting a false precision that nothing in the evidence supports.

Why do the four formulas disagree?

Because they were never meant to agree. Devine, Robinson, Miller and Hamwi are four different people's rules of thumb from four different decades, each fitted to a different purpose. Their disagreement — several kilograms for the same person — is the most informative thing about them.

Where do these formulas come from?

Clinical drug dosing. Devine's, the most copied, was published in 1974 in a one-page note about gentamicin, with no study behind the numbers — it was a convenient rule for estimating how much of a drug to give someone. They were never health targets, and they persist mainly because everyone copies everyone.

Which number should I actually use?

The healthy range in the header, which comes from BMI. It is the only figure on the page derived from health outcomes rather than dosing convenience. Treat the formulas as historical context.

Is BMI reliable?

As a population measure, yes; as a verdict on an individual, less so. It knows only height and weight, so it cannot tell muscle from fat — a lean, muscular person can sit above the range in excellent health, and someone within it can carry a lot of fat and little muscle. Waist measurement and body composition tell you more.

Why does it warn me if I am under five feet?

Every formula is stated as "this many kilograms, plus this much per inch over five feet", and none says anything about heights below that. Extending the line downwards is the usual practice but it is extrapolation, so the tool says so. The BMI range does not have this problem.

Is this medical advice?

No. None of these numbers accounts for build, muscle, age, health history or anything else that matters. If you are trying to decide whether your weight is a health concern, that is a conversation with a doctor, not with a formula from 1974.