Reverse BMI Calculator
Enter a BMI and your height, and this works the formula backwards to give you the weight that produces it.
Weight = BMI × height in metres, squared. A reverse BMI calculator runs the standard BMI formula backwards: instead of turning your weight into an index, it turns an index back into a weight. At 1.78 m, a BMI of 22 is about 69.7 kg.
The formula, both ways
| Metric | Imperial | |
|---|---|---|
| Forward (weight → BMI) | BMI = kg ÷ m² | BMI = lb × 703 ÷ in² |
| Reverse (BMI → weight) | kg = BMI × m² | lb = BMI × in² ÷ 703 |
The 703 in the imperial version is not a separate rule — it is just the unit conversion between pounds-per-inch-squared and kilograms-per-metre-squared folded into a single constant. Both forms give the identical BMI.
Weight at each BMI threshold, by height
Because BMI scales with the square of height, the same BMI is a very different weight at different heights. These are the three WHO boundary weights, rounded to the nearest pound.
| Height | BMI 18.5 | BMI 25 | BMI 30 |
|---|---|---|---|
| 5 ft 0 in (152 cm) | 95 lb / 43 kg | 128 lb / 58 kg | 154 lb / 70 kg |
| 5 ft 4 in (163 cm) | 108 lb / 49 kg | 146 lb / 66 kg | 175 lb / 79 kg |
| 5 ft 8 in (173 cm) | 122 lb / 55 kg | 164 lb / 75 kg | 197 lb / 89 kg |
| 5 ft 10 in (178 cm) | 129 lb / 58 kg | 174 lb / 79 kg | 209 lb / 95 kg |
| 6 ft 0 in (183 cm) | 136 lb / 62 kg | 184 lb / 84 kg | 221 lb / 100 kg |
| 6 ft 4 in (193 cm) | 152 lb / 69 kg | 205 lb / 93 kg | 246 lb / 112 kg |
What this number is, and what it is not
A weight derived from a BMI is arithmetic, not a recommendation. The calculator will happily tell you the weight for a BMI of 17 — that does not make 17 a sensible thing to aim for, and the tool labels any figure you enter against the WHO bands for exactly that reason.
BMI compares your mass to your height and nothing else. It cannot tell muscle from fat, so it reads high for people who carry a lot of lean mass and can read reassuringly normal for someone with significant abdominal fat and little muscle. It says nothing about where fat is stored, which is the part most closely tied to cardiometabolic risk.
It also is not equally calibrated across populations. Several health bodies use lower thresholds for people of South Asian and Chinese descent, because risk rises at a lower BMI than the standard cut-offs suggest. The 18.5–24.9 band is a description of a population distribution, not a personal target, and the healthy-weight range shown with your result is deliberately a range rather than a single ideal figure.
Where to go from a target weight
If you have a weight in mind and want to know what reaching it would involve, the weight loss timeline calculator works out how long a given rate of change takes, and the calorie deficit calculator turns that rate into a daily energy figure. For a check that responds to fat distribution rather than total mass, the waist-to-height ratio calculator is a better instrument than BMI. To run the calculation the usual way round, use the BMI calculator, and ideal weight compares the classic Devine, Robinson, Miller and Hamwi formulas, which answer a related but different question.
Sources: WHO — Obesity and overweight fact sheet (BMI formula and adult cut-offs); NHLBI/NIH — Calculate Your BMI (imperial 703 factor and category ranges); NICE CG189 (lower BMI thresholds for South Asian and Chinese populations); Keys A, et al. — Indices of relative weight and obesity (J Chronic Dis, 1972). Educational estimate, not medical advice. Talk to a doctor or registered dietitian before setting a weight goal.
Frequently asked questions
What is a reverse BMI calculator?
A normal BMI calculator takes your height and weight and returns a BMI. A reverse BMI calculator runs the same formula backwards: you give it a BMI and a height, and it returns the weight that would produce that BMI. The arithmetic is BMI multiplied by your height in metres squared. It is useful for translating a BMI figure into a weight you can actually recognise on a scale.
How do you calculate weight from BMI and height?
Weight in kilograms equals BMI multiplied by height in metres, squared. For example, at 1.78 m a BMI of 22 works out as 22 × 1.78² = 22 × 3.1684 ≈ 69.7 kg. In imperial units the equivalent is weight in pounds = BMI × height in inches² ÷ 703, because 703 is the conversion factor built into the imperial BMI formula.
What weight gives a BMI of 25?
It depends entirely on height, because BMI scales with height squared. At 5 ft 4 in (163 cm) a BMI of 25 is about 66 kg or 146 lb. At 5 ft 10 in (178 cm) it is about 79 kg or 175 lb. At 6 ft 2 in (188 cm) it is about 88 kg or 195 lb. BMI 25 is the threshold where the WHO classification moves from healthy weight to overweight.
Is there an ideal BMI to aim for?
No single number is right for everyone. The WHO healthy-weight band for adults runs from 18.5 to 24.9, which is a range rather than a target, and where an individual sits within it is not something BMI can answer. BMI does not distinguish muscle from fat, does not account for where fat is stored, and was designed to describe populations rather than individuals. If you are setting a weight goal, that is a conversation to have with a doctor or a registered dietitian who can look at more than one number.
Why does BMI use height squared?
The index was devised by Adolphe Quetelet in the 1830s as a way of comparing weight across people of different sizes, and squaring height was the adjustment that made the resulting figure roughly independent of height in the populations he studied. It is a statistical convenience rather than a biological law, which is one reason BMI behaves less well at the extremes of height.
Does BMI work the same for everyone?
No. The same BMI carries different health implications across ethnic groups — several health bodies apply lower thresholds for people of South Asian, Chinese and some other backgrounds, because cardiometabolic risk rises at a lower BMI. It also reads high for muscular people and can read normal for someone carrying significant abdominal fat. Waist-to-height ratio is often more informative about where fat actually sits.
Sources
- WHO — Obesity and overweight fact sheet — BMI formula and adult cut-offs 18.5/25/30
- NHLBI/NIH — Calculate Your BMI — Imperial BMI formula and the 703 conversion factor
- NICE CG189 — Obesity: identification, assessment and management — Lower BMI thresholds for South Asian and Chinese populations
- Keys A, et al. — Indices of relative weight and obesity (J Chronic Dis, 1972) — Origin and validation of the Quetelet index
The thresholds and formulas used by this calculator follow the primary sources above. This tool provides general information, not personalised medical advice.