"Ideal weight" formulas all produce a single number — but a single number, by definition, can't represent a range, and the difference between "a single target" and "a healthy range" matters enormously for how these numbers should actually be used
The previous articles on this site covered the origins of ideal-weight formulas (drug dosing), set-point theory, and why these formulas break down for athletes. This article addresses a more basic, but consequential, framing issue: "ideal weight" formulas output a single number — while health guidance (BMI ranges, covered in previous BMI articles, and broader health recommendations) is generally expressed as ranges, not single targets — and treating a single-number "ideal weight" output as the one "correct" target, rather than a point within (or near) a broader healthy range, creates several practical problems.
"Ideal weight" formulas vs BMI ranges: different shapes of output
BMI categories (covered in previous articles) define ranges — "normal" weight, for a given height, corresponds to a range of weights (those producing a BMI between roughly 18.5 and 24.9) — not a single value.
"Ideal weight" formulas (Devine, Robinson, Miller, Hamwi, and others — covered in the previous drug-dosing-origins article) each produce a single number, for a given height — e.g., "for a height of 170cm, the Devine formula gives an ideal weight of 65.3kg."
These are fundamentally different kinds of output — a range (BMI-based "normal" weight range, which, for 170cm, might span, say, roughly 53-72kg) vs a single point (the formula's 65.3kg) — the single-point "ideal weight" figure typically falls somewhere within the BMI-based "normal" range — but representing it as "the ideal," rather than "one point within a broader range that's generally considered healthy," can create a misleading impression of precision/singularity that the underlying health guidance (BMI ranges) doesn't actually support.
Why "a single target" framing can be counterproductive
Psychologically/behaviorally, framing health-related weight goals around a single, precise number — rather than a range — can create several issues:
"Missing the target" feels like failure, even when within a healthy range: if someone's current weight is, say, 68kg, and "the ideal weight" (per a formula) is 65.3kg — being "2.7kg away from ideal" might feel, to some people, like "not yet healthy" — despite 68kg likely falling, itself, within the BMI-based "normal" range for most heights in this general vicinity — the single-number framing can create a sense of "falling short" that doesn't reflect the underlying health guidance, which would consider both 68kg and 65.3kg (and the range between, and around, them) as "healthy."
Precision-seeking behaviors: a single, precise-seeming "target" number can, for some individuals, encourage excessive precision-seeking in pursuit of that exact number — behaviors like very frequent weighing, significant distress over small (and, as covered in previous body-fat-tracking articles, largely meaningless, hydration-driven) day-to-day weight fluctuations, or restrictive behaviors aimed at "hitting the exact number" — none of which are supported by the underlying health guidance, which, again, is range-based, not single-point-based.
What "ideal weight" formulas can reasonably be used for
Despite the framing concerns above — "ideal weight" formulas aren't entirely without use — their original purpose (drug dosing calculations, covered in the previous article) remains a legitimate, narrow application — clinical contexts where a specific, single number is genuinely needed as an input to a further calculation (like dosing formulas) have a genuine need for a single number — this is different from "what weight should I, personally, be aiming for, for general health purposes."
For general-audience, health-oriented purposes — the BMI-range framing (or broader health-guidance discussions, which may incorporate factors beyond weight/BMI alone — body composition, waist circumference, and other factors covered in various previous articles) is generally the more appropriate framing — with "ideal weight" formula outputs, if referenced at all, understood as "one illustrative point within (or near) the broader healthy range," rather than "the one, precise, correct target."
"Healthy weight range" as the more useful framing
Rather than "what is my ideal weight" (a single number) — "what is my healthy weight range, for my height" (derived from BMI category boundaries, as covered in previous BMI articles) — provides a range within which multiple different weights would all be considered, for BMI purposes, "normal"/"healthy."
This reframing:
- Removes the "missed the target by 2.7kg" framing — any weight within the range is, for BMI*-based purposes, "on target"
- Better reflects individual variation — two people of the same height, with different (but both "normal"-range) body compositions, frame, muscle mass, etc. — might reasonably have different "healthy" weights, both within the range, without either being "more correct" than the other
- Aligns directly with the actual clinical/public-health guidance (BMI categories), rather than introducing a separate, additional, single-number "target" that isn't itself part of that guidance
How to use the Ideal Body Weight Calculator on sadiqbd.com
- Recognize the formula outputs as reference points, not targets — useful for understanding "roughly where, within the healthy range, does this formula's output fall" — not as "the number I should be trying to reach"
- Cross-reference with the BMI Calculator's range — for your height, what's the full "normal" BMI-based weight range? Where, within (or relative to) that range, do the "ideal weight" formula outputs fall? This comparison provides more useful context than the single-number output alone
- For clinical/dosing contexts specifically: if you (or a healthcare provider) genuinely need a single-number "ideal weight" as input to a specific clinical calculation — the formulas remain useful for this narrow, original purpose
Frequently Asked Questions
If I'm at the edge of the "normal" BMI range, is that "less healthy" than being in the middle? BMI categories represent thresholds derived from population-level statistical associations (covered, in general*, in previous BMI articles) — the "normal" range isn't internally "graded" such that the middle is "better" than the edges — being anywhere within the "normal" range is, for BMI-based purposes, treated as "normal"* — though, as covered extensively in previous BMI-limitations articles, BMI itself has significant limitations as a sole measure of health — factors beyond BMI (body composition, waist circumference, overall health markers) are generally more informative than "where, precisely, within the BMI 'normal' range, does someone fall."
Is the Ideal Body Weight Calculator free? Yes — completely free, no sign-up required.
Try the Ideal Body Weight Calculator free at sadiqbd.com — see reference estimates alongside the broader healthy BMI-based weight range for your height.
