Ideal Weight Calculator

What is ideal body weight?

Ideal body weight (IBW) is a reference estimate of the weight associated with better health outcomes for a person of a given height and sex. The concept was not born in fitness culture. It first appeared in clinical medicine around the middle of the twentieth century as a way to standardize drug dosages, because the metabolism of many medications in the slot of a person's apparent frame correlates more strongly with skeleton and muscle mass than with total body weight. Over the decades the same formulas spread into surgery, anaesthesia, sports weight classes and everyday wellness conversations, since competitions and screenings need a single comparable number.

While a single number sounds convenient, no integer can capture the full story of a healthy body. Muscle mass, bone density, blood volume and body fat all shift what is realistic for one person versus another of identical height. This tool therefore follows the classical approach: it computes your ideal weight from four established formulas and pairs the outputs with the healthy body mass index (BMI) band for your height, so you get an evidence-based range instead of an illusion of precision.

To understand where you are right now, check your status with the BMI calculator and compare it with the estimates below to see whether your current weight sits inside the healthy band, above it or under it.

How this calculator works

The calculator needs just two inputs: your sex and your height. Height is entered in centimetres by default, with a quick option to switch to inches. From those inputs it first works out how many inches your height stands above five feet, because all four classic formulas share one skeleton:

IBW (kg) = base weight (kg) + increment (kg per inch) × inches over five feet

Each formula only differs in the base weight and the per-inch increment its author calibrated from the population they studied. The constants used in this calculator are listed below:

For a person measuring five feet ten inches, the formula adds ten inches on top of the base value. If a height below five feet is entered, the equations still evaluate cleanly and return a value below the base, matching the behaviour of most reference implementations placed elsewhere. That edge case rarely matters in practice, but it is handled.

Comparing the four formulas

The side-by-side outputs are not decoration: the formulas genuinely disagree about the same body. At a height of 178 cm (about 5 ft 10 in), a man receives roughly 73 kg from the Devine equation, about 71 kg from Robinson, close to 67.9 kg from Miller, and more than 74.5 kg from Hamwi. The compression between published studies is exactly why displaying all four is useful: it shows the spread of opinion among researchers instead of pretending there is one authoritative constant.

Here is a feel for how they rank. Hamwi, the earliest formula, tends to assign the highest weights because of its aggressive increments per inch. Robinson and Miller run lower on average, with Miller the most conservative of the four. Devine settles in the middle, and — as a historical accident of hospital practice — remains the one most frequently cited by physicians and pharmacists. None of them is objectively wrong; they simply answer slightly different statistical questions.

If you want a single headline number, lean on Devine and treat the healthy BMI band as your actual decision interval. The gap between the formula outputs and the top of the BMI band is informative: for many active adults the formula sits lower, which is a gentle reminder that IBW is a target range for prescribing, not a mandate against muscle gain.

The healthy BMI weight range

The World Health Organization standard healthy BMI band for adults is 18.5–25 kg/m², the metric that classifies underweight, normal, overweight and obesity. BMI is a weight against the square of height:

BMI = weight (kg) divided by height (m) squared

Rearranged, that equation directly gives the healthy weight interval for your exact height:

Healthy weight (kg) = 18.5 × height² up to 25 × height²

For a 170 cm person, that band spans roughly 53.5 to 72.3 kg. The bar chart in the results panel draws the weight for every BMI value between 18.5 and 25 at the height you entered, effectively sketching the interval you should aim for. BMI is admittedly a blunt instrument — it cannot separate muscle from fat — but it remains the standard screening metric for adult weight categories, and it anchors the healthy window shown by this calculator.

Combined with your body fat percentage, a high BMI becomes easier to interpret. Use the body fat calculator to see whether your weight mostly sits in muscle or in fat, then set the pace with the calorie calculator so that your daily intake moves you toward the band smoothly.

What is wrong with a single ideal number?

Let us name the elephant: the four formulas ignore age, frame size and body composition. A distance runner and a powerlifter of the same sex and height receive the same IBW, although their healthy weights can differ by many kilograms. Frame size alone means a broad-shouldered person naturally carries more bone and muscle at the same height than somebody with a small frame, and no classical equation folds that in.

Age also matters past adulthood. The formulas assume a fully grown skeleton, but in practice lean mass gradually declines from the thirties onward while fat tends to accumulate, so a number computed at 160 cm describes the average twenty-something better than the average seventy-year-old, even though the printed result is identical. Height itself can shrink by a centimetre or two in old age, quietly moving the marker. Muscular individuals can exceed the top of the BMI band while staying metabolically healthy, and conversely some people sit inside the normal band while carrying too much fat — sometimes called normal weight obesity.

Interpreting your results

Rather than treating the four outputs as a verdict, use them as follows:

• Look at the spread of the four formulas. If they cluster within a kilogram or two, your height falls exactly where the authors calibrated; wider spreads mean the constants drift apart at your height.
• Anchor on the healthy BMI band. It is far more meaningful than the apparent accuracy of any single formula.
• Compare your current weight against the band in the summary card, then use the BMR calculator to size your baseline calorie burn correctly for whatever adjustment you plan.
• If you then build a meal plan, the macro calculator breaks a calorie target into protein, carbohydrate and fat portions that make the weight goal achievable without guesswork.

A sustainable pace is about half a kilogram to one kilogram per week for fat loss, and significantly less for gaining lean mass. Larger day-to-day swings in the common scale mostly reflect water and glycogen, which is why week-over-week averages beat single weigh-ins.

When ideal weight does not apply

The formulas are adult equations. For children and teenagers, healthy weight is judged against age- and sex-specific BMI percentile charts, because growth spurts make an absolute number meaningless before age 18. During pregnancy, the ideal-weight equations deliberately do not include the weight gain that obstetric guidelines track across trimesters. People with amputations, medical dwarfism or extreme muscular development sit outside the calibration window: for them a clinic team, not a printed table of constants, should decide what healthy looks like.

Above all, remember the origin story of these formulas: they were developed for medication dosing, not for fashion magazines. They are at their best as reasonable anchors inside a range-based view of weight, which is precisely the framing this page already gives you via the WHO band.

Ideal weight and weight goals in practice

Once the summary card shows your four formula estimates and the healthy band, the next natural step is defining a plan. A useful shortcut: if your current weight is above the top of the band, work backwards from the band's upper end — not from a dream number — to set the distance you actually need to travel. If you are inside the band, ask yourself whether your body fat percentage supports the association, because the same kilogram can belong to very different physiques.

For people training, the classical formulas are only the starting point. An athlete who aims for a competition weight class can use the outputs to scout where the judges will weigh you and then check the difference against their body fat readings. For anyone managing a medical condition, the IBW numbers can guide dose calculations in conversation with a doctor — the original purpose of the constants. Notice how each use case wants a slightly different output: the formula number for clinical contexts, the range for everyday health, and the cartilage of the general band.

Weight change happens slowly by design. Sustained habits of protein at each meal, regular movement and moderate calorie control beat any aggressive start. Re-measure weekly, average the readings, and watch the trend against the band shown here rather than chasing any single morning scale. If the trend stalls for four or more weeks, revisit either the calorie target from the calorie calculator or the activity assumptions you fed into the BMR estimate; usually one of the two shifted silently.

When the numbers start moving, it is better to anchor on the healthy range than on the formula. The range is where medical research puts the low-risk zone for all-cause health; the formulas simply give historical opinion a name. A body that lands anywhere inside the band, with lean mass preserved, is a body that has already achieved the core goal this page was built to orient.

Conclusion

The ideal weight question carries a tidy mathematical answer and a messier real-world one. This calculator layers the classic Devine, Robinson, Miller and Hamwi equations over the WHO healthy band, so you can see the historical targets and the evidence-based interval in the same screen. Start with the range, let the formulas calibrate expectations, and use the additional tools — BMI, body fat, calorie intake — to design the slow and steady path into it.

Disclaimer

Results are provided as estimates for informational purposes only and may be inaccurate. Always verify outcomes with a qualified professional before making financial or personal decisions based on these calculations.