Does frame size really matter?
Yes. A person with a large frame (heavy bone structure) naturally weighs more than someone with a small frame, even at the same body fat percentage. Most IBW formulas assume a 'medium' frame. Large-framed individuals should add 10%, and small-framed individuals should subtract 10%.
Why is the Devine formula the standard?
It was widely adopted by pharmacists for drug dosing in the 1970s because it was simple and accurate enough for clinical safety. Its widespread use in hospitals cemented it as the 'default' IBW calculation, even if newer formulas like Robinson might be slightly more accurate for modern populations.
Is it healthy to be below my Ideal Body Weight?
Generally, no. Being significantly below your IBW (more than 10-15%) can indicate being underweight, which carries risks like weakened immunity, osteoporosis, and hormonal disruptions (amenorrhea in women). 'Ideal' implies the weight where your body functions best, not the lowest possible weight.
How do I calculate IBW for children?
You don't. Children grow at variable rates. Pediatricians use 'Growth Charts' (percentiles) to track whether a child is growing on their own curve. Applying adult IBW formulas to children is inaccurate and potentially harmful.
Can I use this calculator if I am pregnant?
No. Pregnancy requires specific weight gain to support the baby. Your pre-pregnancy IBW can serve as a baseline to determine how much weight you *should* gain (e.g., 25-35 lbs), but it is not a target to maintain during pregnancy.
What if I am an athlete?
Athletes should view IBW with skepticism. Muscle is dense. A rugby player or weightlifter will almost always be 'Overweight' or 'Obese' according to IBW and BMI, despite having low body fat. For athletes, Body Fat Percentage is the only metric that matters.
Why do the formulas only use height and gender?
They were designed in an era before easy body fat testing. Height and gender were the two most predictive variables for 'healthy mass' that could be easily measured in a doctor's office. While simple, they remain surprisingly effective for the general non-athletic population.
How often should I check my IBW?
Your IBW doesn't change unless your height changes (which happens slightly as we age). However, comparing your *actual* weight to your IBW is a good annual check-up to ensure you aren't experiencing 'weight creep'—the slow addition of 1-2kg per year that leads to obesity over decades.
Is the Hamwi formula better for women?
Many dietitians prefer Hamwi for women because it tends to yield a slightly lower, more 'petite' range that aligns with the expectations of smaller-framed women. However, Devine is still the medical standard for dosing.
Does muscle weigh more than fat?
A pound is a pound. However, muscle is much more *dense* than fat. One pound of muscle takes up roughly 18% less space than one pound of fat. This is why you can look smaller and leaner at 70kg (muscular) than you did at 68kg (fat).