Ideal weight calculator

How ideal weight is calculated

All four formulas below start from the same idea: pick a baseline weight for someone 5 feet (152 cm) tall, then add a fixed amount for every inch above that. None of them measure body fat, waist size or frame, only height and sex go in.

Step 1: height over 5 feet

The calculator converts your height to inches and subtracts 60, since 5 feet equals 60 inches. Someone 175 cm tall is about 68.9 inches, so that is 8.9 inches over the 5 foot baseline. This single number, inches over 5 feet, drives every formula below.

Step 2: baseline plus increment

Each formula sets a baseline weight for a 5 foot adult, then multiplies the inches over 5 feet by a fixed increment per inch. The baseline and the increment are what differ between the four formulas, which is why they never agree exactly.

Take a 175 cm (5 ft 9 in) man as a worked example. That is 8.9 inches over 5 feet. Devine's formula, a 50 kg baseline plus 2.3 kg per inch, gives 50 + 2.3 x 8.9 = 70.5 kg. Robinson's formula, a 52 kg baseline plus 1.9 kg per inch, gives 52 + 1.9 x 8.9 = 68.9 kg. The two land less than 2 kg apart, which is typical.

How much a height measurement error matters

Because every formula runs on inches over 5 feet, the increment per inch sets how much a mismeasured height moves the result. Devine's 2.3 kg per inch is the steepest of the four, so a height that is off by half an inch, easy to do standing without shoes against a door frame instead of a proper stadiometer, shifts Devine's number by about 1.15 kg. Miller's smaller 1.41 kg per inch increment moves by less than 0.75 kg for the same error. None of that comes close to the gap that already exists between the four formulas at a typical height, so a rough height measurement is a minor source of error next to the choice of formula itself.

The four formulas, and why they differ

The four equations were all published to answer one clinical question: what weight should a pharmacist plug into a drug dose calculation for a patient. They share a shape but were fitted to different reference populations, which is why they never land on the same number.

Devine (1974)

Published by Dr B.J. Devine as a rough rule of thumb for calculating gentamicin doses, not as a formal research finding. It uses a 50 kg baseline for men and 45.5 kg for women, plus 2.3 kg per inch over 5 feet for both. It became the default in pharmacy because it is the simplest to calculate by hand, and it remains the most widely used ideal weight formula in clinical dosing today.

Robinson (1983)

Adjusted Devine's baseline slightly, to 52 kg for men and 49 kg for women, using a larger reference dataset. It gives a marginally lower result for taller people because it uses a smaller per inch increment: 1.9 kg for men and 1.7 kg for women.

Miller (1983)

Uses the smallest per inch increment of the four, 1.41 kg for men and 1.36 kg for women, with a higher baseline. It tends to sit closest to average adult weight at average heights and drifts furthest from the other three at the extremes of height.

Hamwi (1964)

The oldest of the four, originally published in pounds: 106 lb plus 6 lb per inch for men, 100 lb plus 5 lb per inch for women. It predates the others and is still taught in nutrition and nursing courses, though Devine has largely replaced it in pharmacy practice. This calculator uses the standard metric restatement of that formula, 48.0 kg plus 2.7 kg per inch for men and 45.5 kg plus 2.2 kg per inch for women, which is the rounded conversion used in most metric references rather than a fresh conversion of the pound figures at every height.

None of the four is officially endorsed as more correct than the others. Devine is the de facto default because it appears in the most published drug dosing protocols, which is why this calculator leads with the average across all four rather than picking a single winner.

The four formulas typically land within a few kilograms of one another for the same patient at adults of average height, widening slightly at the tallest and shortest ends of the range where each formula's baseline and increment matter more.

The healthy BMI weight range

Alongside the four historical formulas, the calculator shows the weight range that keeps your BMI between 18.5 and 24.9, the band the World Health Organization classifies as normal weight for adults. Unlike the four formulas above, this is a range rather than a single number, because BMI treats a wide span of weights as equally healthy at any given height.

For a 175 cm adult that band runs from about 56.7 kg to 76.3 kg, a span of almost 20 kg. The four ideal weight formulas, by contrast, cluster within about 3 kg of each other. That gap is the clearest sign that ideal weight formulas and the BMI healthy range answer different questions: one gives a dosing weight, the other a population health range. Use the BMI calculator to check yours directly.

The four formulas at a glance

Figures below are for a 175 cm (5 ft 9 in) adult, split by sex. Your own numbers will differ; use the calculator above for your exact height.

Why these are drug dosing formulas, not aesthetic targets

Every one of the four formulas above was built to answer a clinical dosing question: what weight should a pharmacist enter into an antibiotic, chemotherapy or anaesthesia dose calculation for a patient well above or below average weight, where using actual body weight would overdose or underdose them. None of the four studies measured body fat, muscle mass, frame size or what a healthy body should look like.

That distinction matters because the formulas only ever look at height and sex. A 90 kg bodybuilder at 12 percent body fat and a 90 kg person carrying most of that weight as fat get the same ideal weight number, even though one of them is nowhere near overweight by any meaningful measure. For dosing that is fine, a drug does not care how the weight is made up. For deciding what you should weigh, it is close to useless.

If your goal is a body composition target rather than a dosing weight, a body fat percentage from the Navy body fat calculator or a result from the lean body mass calculator answers a far more useful question: how much of your weight is fat, not what an average person your height weighs.

Clinicians who still use these formulas for dosing now often pair them with adjusted body weight, which blends ideal weight with actual weight for patients well above their ideal range, because using ideal weight alone under-doses drugs that also distribute into fat tissue. That refinement alone shows the formulas were never meant to define a target physique.

It is also worth knowing that none of the four formulas has been revalidated against modern body composition data such as DEXA scans. They were fitted decades ago against whatever reference weight tables existed at the time, which is a reasonable basis for a rough dosing estimate and a weak basis for a personal weight goal.

How to use your ideal weight number

Treat it as a midpoint, not a target

The four formulas cluster within a few kilograms of each other for most heights, so if you fall inside that cluster you are already inside the range every formula broadly agrees on. There is no health reason to chase the exact centre of it.

Use the BMI range for a broader check

Because the four historical formulas were built for dosing, the BMI calculator and its 18.5 to 24.9 band is the better reference if you are asking a general health question rather than a clinical one. It is wider and reflects the population data behind the WHO classification directly.

Go further with body composition

If you train regularly, weight alone stops being a useful signal. Two people at the same ideal weight can carry very different amounts of muscle and fat. A body fat percentage from skinfolds, a scan or the Navy method, paired with the lean body mass calculator, gives a far more actionable picture than any single weight number.

Common mistakes

Treating one formula as the correct one. None of the four has been shown to be more accurate than the others for general use. Averaging them, as this calculator does, is more honest than picking whichever formula gives the number you want.

Using it as a goal weight for training. The formulas do not know whether you lift weights. Muscle adds weight without adding health risk, so an athletic person can sit well above every formula's number and still be in excellent shape.

Applying it below 5 feet (152 cm). All four formulas use 5 feet as their baseline height and add nothing below it, so a result for someone shorter than that is just the baseline weight for their sex, not a real estimate for their height.

Ignoring frame size within a group. A small framed and a large framed person of the same height and sex can both be healthy at noticeably different weights. None of these formulas can see frame size at all.

Confusing dosing weight with a diet target. A pharmacist uses ideal weight to size a drug dose safely, not to tell a patient what to weigh. Using it as a weight loss goal borrows a number that was built for the wrong purpose.

How coaches use an ideal weight calculator

For a trainer, an ideal weight number from any of these four formulas is a conversation starter, not a plan. It tells you almost nothing about a new client's training history, body composition or goals, so the useful next step is a body fat estimate and a proper intake, not a weight target.

A more workable use: run the calculator at intake alongside a body fat calculation, note whether the client sits inside or outside the BMI healthy range, then set the real targets, calories, training split and check-in cadence, based on what the client actually wants to change. Explaining upfront that these are dosing formulas, not a verdict on their physique, heads off a lot of unnecessary discouragement in that first conversation.

Scraler replaces the spreadsheet version of this. Log a client's stats, body fat and progress photos over time, set nutrition targets per client, and review the trend in weekly check-ins instead of a single weight number frozen at intake. See nutrition coaching for how targets connect to what a client logs.

Ideal weight vs adjusted body weight in dosing

Clinicians rarely stop at ideal body weight once a patient sits well above it. Ideal weight alone assumes a drug distributes only into lean tissue, which is true for some drugs and badly wrong for others. Fat tissue is not metabolically inert, it holds blood volume, some fluid and, for certain lipophilic drugs, a meaningful share of the dose itself. Using ideal weight for those drugs in a heavier patient systematically under-doses them, which is exactly the failure adjusted body weight was built to correct.

Adjusted body weight blends ideal weight with actual weight using a correction factor, typically written as ideal weight plus 0.4 times the difference between actual weight and ideal weight. The 0.4 factor is itself an approximation, derived from pharmacokinetic studies estimating how much extra distribution volume a kilogram of excess weight adds compared with a kilogram of lean tissue. It is not universal. Some drug classes use a different correction factor, and some protocols skip the adjustment entirely and dose from actual body weight with a hard cap, depending on how the specific drug behaves in the body.

When each weight gets used

For a patient close to their ideal weight, the distinction barely matters since actual, ideal and adjusted weight sit close together. The gap opens up for patients well above their ideal weight, where actual body weight would overdose a drug that mostly avoids fat tissue, and ideal weight alone would underdose a drug that partly distributes into fat. Adjusted body weight exists specifically for that middle case, and mainly shows up in dosing protocols for antibiotics like gentamicin and vancomycin, some chemotherapy agents, and certain sedatives used in anaesthesia.

Why this calculator does not compute it

Adjusted body weight is drug specific. The correct correction factor, and whether one should be applied at all, depends on which medication is being dosed, which is a clinical decision made by a prescriber with the specific drug's pharmacokinetic profile in hand, not a general height and sex calculation. This calculator reports the four ideal weight formulas because they are general purpose and drug agnostic; adjusted body weight intentionally is not, and publishing one general adjusted figure here would imply a precision the number does not have without knowing the drug in question.

The practical takeaway for a non-clinical reader is narrower: if you have seen the term adjusted body weight used in a medical context, it is a dosing refinement built on top of ideal body weight, not a different or more accurate estimate of what you personally should weigh. It answers a pharmacology question, the same way the four formulas above do, and carries the same limitation of ignoring body composition entirely.