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Amputee BMI Calculator (Adjusted Body Weight After Amputation)

Calculate an adjusted BMI after limb amputation: estimate the weight with the missing limb using Osterkamp body-segment percentages, then the corrected BMI and category.

Current weight

Height (before amputation)

Missing limb segment

Number of limbs at this level

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How it works

Estimated weight = current weight ÷ (1 − proportion missing) · adjusted BMI = estimated weight ÷ height (m)² · segment shares (Osterkamp): hand 0.7%, forearm 1.6%, upper arm 2.7%, entire arm 5.0%, foot 1.5%, lower leg 4.4%, thigh 10.1%, entire leg 16.0%

After an amputation, the BMI from current weight is falsely low because the missing limb no longer counts, even though height is unchanged. Osterkamp (1995) recommended estimating what the person would weigh with the limb, using the average share of body weight carried by each body segment, and calculating BMI from that estimate. Shares add up: a below-knee amputation removes the foot (1.5%) and lower leg (4.4%) = 5.9%; an above-knee amputation leaves part of the thigh, so 16% (the whole leg) is an upper bound.

Worked example

A person weighing 68 kg at 175 cm with one below-knee amputation (5.9%): estimated weight = 68 ÷ (1 − 0.059) = 68 ÷ 0.941 = 72.3 kg; adjusted BMI = 72.3 ÷ 1.75² = 23.6 (normal weight). The unadjusted BMI would be 22.2.

Sources: Osterkamp LK (1995) Current perspective on assessment of human body proportions of relevance to amputees. J Am Diet Assoc 95:215–218

Frequently asked questions

How do you calculate BMI for an amputee?

Divide the current weight by (1 − the proportion of body weight that is missing) to estimate the full-body weight, then divide by height in metres squared. For a below-knee amputation the proportion is 0.059.

Should I weigh with or without the prosthesis?

Weigh without the prosthesis. If you must weigh with it, subtract the prosthesis weight first, because the equation assumes the limb is entirely missing.

Which height should I use?

Use the standing height before amputation, if known. Otherwise arm span or knee height on the intact leg can estimate it.

What about an above-knee amputation?

The share depends on how much thigh remains: between 5.9% (just above the knee) and 16% (hip disarticulation). Many dietitians use about 10–16% depending on residual limb length; choosing 16% gives the most conservative (highest) adjusted BMI.

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This calculator is an educational aid for nutrition and health professionals. It does not replace a clinical assessment — measurement technique strongly affects the result, so interpret it with a qualified professional.