On a a scale, 65 kg for a woman who is 1.70 m tall tells a different story depending on whether she is 25 years old with regular sports practice or 55 years old after two pregnancies. The number alone does not convey anything about the distribution between fat mass and muscle mass, nor about the actual state of health. Calculating a reference weight for this height requires understanding what the available formulas really measure, and especially what they do not measure.
Hospital origin of ideal weight formulas for 1.70 m
We often talk about the Lorentz, Creff, or Devine formulas as if they were designed to help choose a weight loss goal. Their history is quite different. The Hamwi, Devine, Robinson, and Miller formulas were created between the 1960s and 1980s for a specific use: to adjust medication dosages for hospitalized patients.
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The calculation was based on the patient’s height to estimate a reference body mass, in order to correctly dose anesthetics or antibiotics. These tools were never intended to define an aesthetic goal or a “good” weight for everyday life.
When trying to determine the ideal weight for a woman who is 1.70 m tall, one comes across these same formulas recycled by dozens of online calculators, without mention of their original context. The result displayed varies by several kilograms from one formula to another for the same person, which should be enough to put the claimed precision into perspective.
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BMI for 1.70 m: what the 18.5-24.9 range hides
The body mass index remains the only measure officially used by health organizations. The formula is simple: weight in kilograms divided by height in meters squared. For a woman who is 1.70 m tall, the so-called “normal” range (BMI between 18.5 and 24.9) corresponds to a weight between 53 and 72 kg.
This range of nearly 20 kg clearly shows that BMI does not distinguish between fat and muscle. A woman who works out three times a week may have a BMI of 25 while having a low body fat percentage and no cardiovascular risk factors.
Age shifts the reference range
Recent data show that the BMI range associated with the lowest risk of mortality evolves with age. Between 19 and 24 years, a BMI of 19 to 24 corresponds to the optimal zone. Between 35 and 44 years, this zone shifts to 21-26. After 55 years, a BMI between 23 and 28 is associated with the best prognosis.
In practical terms, for a woman who is 1.70 m tall at 60 years old, a weight around 70-75 kg may be perfectly healthy, while the same weight would be considered borderline at 25 years. The weight goal must take age into account, not just the raw calculation.
Waist circumference and waist-to-hip ratio: indicators that BMI does not replace
Recent tools for assessing body composition no longer rely solely on BMI. Two complementary measurements help detect cardio-metabolic risk even with a normal BMI:
- The waist circumference, measured at mid-distance between the last rib and the top of the hip. Beyond a certain threshold, it indicates an excess of visceral fat, which surrounds the organs and is most associated with chronic diseases.
- The waist-to-hip ratio, which compares the circumference of the waist to that of the hips. It refines the assessment for body types where weight is distributed unevenly between the upper and lower body.
- BMI percentile charts, used for younger individuals but increasingly proposed to contextualize results in adults based on sex and ethnic origin.
One can have a BMI of 23 and a high waist circumference, or a BMI of 26 with a waist circumference within the normal range. The number on the scale is not enough to assess metabolic risk.
Functional approach to weight for a woman who is 1.70 m tall
Modern calculators, whether offered by hospital websites or mobile applications, are evolving towards a different logic. Rather than setting a target number, they associate the calculation with behavioral parameters: sleep quality, stress level, muscle mass, and long-term eating habits.
Muscle mass and metabolism
Muscle loss is the classic trap of restrictive diets. One loses weight on the scale, but the basal metabolism decreases. When food intake resumes, the body stores more and the weight rises beyond the starting point. For a woman who is 1.70 m tall, maintaining or developing muscle mass through regular strength training protects metabolism and stabilizes weight in the long term.
Feedback varies on this point, but most professionals agree on one principle: a stable and maintainable weight is better than a theoretical “ideal” weight that can only be maintained for a few weeks.
Signals to monitor daily
Rather than aiming for a precise number, it is beneficial to observe concrete indicators:
- The energy level throughout the day, without marked fatigue after meals.
- The ability to climb several flights of stairs without disproportionate shortness of breath.
- The stability of weight over several months without severe dietary restrictions.
- The absence of joint pain related to body weight.
These functional markers provide a more reliable picture than any mathematical formula. The weight displayed remains one data point among others, not a verdict.
Calculating a reference weight for 1.70 m makes sense as a starting point, provided it is not treated as a fixed goal. The BMI range, waist circumference, and functional indicators form a trio far more useful than a single number derived from a formula from the 1970s. The body changes with age, physical activity, and life events, and the concept of a healthy weight evolves with it.