Free health calculators for BMI, body fat, ideal weight, body shape, and fitness. Get personalized recommendations and reference ranges.
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Health calculators give you a quick numerical reference point for things like ideal body weight and BMI, drawing on formulas that have been used in clinical and academic settings for decades. They're useful for understanding where you sit relative to population averages and which direction the numbers are moving — they aren't a substitute for medical evaluation.
The calculators here use multiple formulas (Devine, Robinson, Miller, Hamwi, plus the WHO BMI range) because no single formula fits every body. We show all the answers side-by-side so you can see the range, along with explanations of which formula was developed for which use case. For any decision about your health, see a qualified healthcare provider — they have context these calculators can't.
What is "ideal body weight" and why does it exist?
Ideal body weight (IBW) is an estimate of the weight associated with the lowest mortality risk for a given height, developed in the 1960s–80s as a tool for medication dosing (especially in critical care and renal medicine where dosage depends on weight). It's a rough population-level reference, not a personal goal — actual healthy weight depends on muscle mass, frame size, age, and other factors a formula doesn't capture.
Which ideal weight formula is most accurate?
No single formula is "most accurate" — they were each developed for different populations and purposes. Devine (1974) is the most common in pharmacology. Robinson (1983) and Miller (1983) modified it to better fit shorter individuals. Hamwi (1964) is simpler and still used clinically. The differences between them are usually small (a few kilograms); seeing all four gives you a range, which is more honest than a single number.
How does ideal weight differ from BMI?
BMI (Body Mass Index) is weight divided by height squared, giving a single number that's compared against population ranges (under 18.5 = underweight, 18.5–24.9 = normal, etc.). Ideal weight formulas instead give you a specific target weight for your height. BMI is the standard for population-level screening; ideal weight formulas remain more common for clinical dosing. Neither accounts for muscle vs. fat.
Why do different formulas give different ideal weights?
Because they were derived from different reference populations and for different purposes. Devine's formula was fit to actuarial data on adults in the U.S. Robinson and Miller adjusted Devine to fit shorter ranges better. Hamwi was developed for diabetic patients. The output gap (typically 2–5 kg) reflects real disagreement among researchers about what "ideal" should mean — which is part of why the concept itself is contested.