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Frame Size Adjusted BMI Calculator

Calculate Ideal Body Weight adjusted for skeletal frame size. Uses Wrist-to-Height ratio to categorize you as Small, Medium, or Large frame.

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About

One of the most common criticisms of standard weight charts is that they do not account for skeletal mass. A person with a thick, broad skeleton ("Large Frame") will naturally weigh more than someone with a delicate build, even at the same body fat percentage. This calculator adjusts the standard Ideal Body Weight (IBW) targets by ±10% based on your frame size.

Frame size is determined objectively using the ratio of body height to wrist circumference ($H/W$ ratio). This method is preferred by insurance actuaries and medical researchers over the subjective "elbow breadth" test.

frame size wrist measurement ideal weight adjusted bmi big boned

Formulas

The ratio ($R$) is calculated as height divided by wrist circumference:

R = H (cm)Wrist (cm)

The Adjusted Ideal Weight ($IBW_{adj}$) is then derived from the standard Devine calculation:

{
IBW × 0.9 if SmallIBW × 1.0 if MediumIBW × 1.1 if Large

Reference Data

Frame SizeRatio (Men)Ratio (Women)Adjustment
Small Frame> 10.4> 11.0Subtract 10%
Medium Frame9.6 - 10.410.1 - 11.0No Adjustment
Large Frame< 9.6< 10.1Add 10%

Frequently Asked Questions

Wrap a measuring tape around the smallest part of your wrist, just below the styloid process (the bony bump on the pinky side). The tape should be snug but not compressing the skin.
Yes, but often less than people think. A large skeleton might account for 2-4kg of extra weight compared to a small skeleton. However, the "Large Frame" category often permits up to 10% more weight to account for the additional muscle mass usually required to move a heavier frame.
If you are on the borderline, it is safer to aim for the lower weight range (Medium instead of Large) for cardiovascular health, unless you are an active athlete with significant muscle mass.