About the Amputee BMI Calculator
Standard BMI underestimates body size after a limb amputation, because the scale no longer weighs the missing segment while height stays the same. Someone with a below-knee amputation who weighs 165 lb, for example, carries the body composition of a person of about 175 lb. Dietitians and rehabilitation teams correct for this by estimating what the person would weigh with all limbs, then calculating BMI from that estimated weight.
This calculator applies the body-segment percentages summarised by Osterkamp (1995) in the Journal of the American Dietetic Association, the reference most often used in clinical nutrition: hand 0.7%, forearm with hand 2.3%, entire arm 5.0%, foot 1.5%, lower leg with foot 5.9% and entire leg 16% of total body weight. Choose the level for each limb and it returns your adjusted weight, adjusted BMI, the BMI category and the healthy weight range expressed for your current body.
Weigh yourself without your prosthesis. Mid-thigh and mid-upper-arm levels are estimated by adding half of the thigh or upper-arm segment; if you know your exact residual-limb length, your clinician can refine it. Segment proportions vary between individuals and with muscle atrophy in the residual limb, so treat the result as an estimate for tracking trends.
With the default inputs, the adjusted bmi is 25.2. Change any value above to recalculate instantly.
How to use the amputee bmi calculator
- 1Choose US or metric units and enter your height (use your pre-amputation height if you cannot stand).
- 2Weigh yourself without your prosthesis and enter that weight.
- 3Select the amputation level for each affected limb.
- 4Read your adjusted BMI, category and estimated full-body weight.
- 5Use the healthy scale-weight range as your target on the scale.
Formula and method
P is the total proportion of body weight represented by the missing segments, summed across limbs. Segment values follow Osterkamp (1995): hand 0.7%, forearm 1.6% (forearm with hand 2.3%), upper arm 2.7% (entire arm 5.0%), foot 1.5%, lower leg 4.4% (lower leg with foot 5.9%) and thigh 10.1% (entire leg 16.0%). A mid-thigh or mid-upper-arm amputation is estimated as the distal segments plus half of the thigh or upper arm.
Dividing measured weight by (1 − P) gives the estimated weight with all limbs, which is then used in the standard BMI formula and compared with WHO adult cut-offs (18.5, 25, 30). The healthy range reverses the process: 18.5 and 24.9 × height² × (1 − P) gives the scale weights that correspond to a healthy adjusted BMI.
- P
- Proportion of total body weight missing (sum of segment percentages ÷ 100)
- measured weight
- Scale weight without prosthesis
- height
- Pre-amputation or measured standing height (m)
Worked examples
Right below-knee amputation, 5 ft 10 in, 165 lb
A lower leg with foot is 5.9% of body weight, so 165 ÷ (1 − 0.059) = 175.3 lb. At 1.778 m tall that is 79.5 kg ÷ 3.161 m² = BMI 25.2, just into the overweight range, while the unadjusted BMI of 23.7 looked healthy.
Bilateral above-knee (mid-thigh), 180 cm, 68 kg (metric)
Each mid-thigh amputation is estimated at 5.9% + half of 10.1% = 10.95%, so 21.9% in total. 68 ÷ 0.781 = 87.1 kg, and 87.1 ÷ 1.8² = BMI 26.9 — overweight, although the scale-weight BMI is 21.0.
Left below-elbow amputation, 5 ft 4 in, 130 lb
Forearm with hand is 2.3% of body weight, so 130 ÷ 0.977 = 133.1 lb. At 64 inches (1.6256 m) that is 60.4 kg ÷ 2.643 m² = BMI 22.8, within the healthy range.
Frequently asked questions
How do you calculate BMI for an amputee?+
Estimate the weight you would have with all limbs by dividing your scale weight by (1 − the proportion of body weight missing), then use that estimated weight in the normal BMI formula. For a below-knee amputation the missing proportion is about 5.9%.
What percentage of body weight is a leg?+
Using Osterkamp’s widely used values, an entire leg is about 16% of body weight, the thigh 10.1%, the lower leg 4.4% and the foot 1.5%. An entire arm is about 5%, made up of the upper arm (2.7%), forearm (1.6%) and hand (0.7%).
Should I weigh myself with my prosthesis on?+
No. Weigh without the prosthesis and other removable devices so the calculation starts from your body weight alone. If you must weigh with it, subtract the prosthesis weight first, which your prosthetist can tell you.
Are the percentages different for men and women?+
Osterkamp’s values are a single set used for both sexes, and that is how dietitians usually apply them. Other body-segment studies report somewhat different proportions for women, and individual build varies, so treat the adjusted figure as an estimate either way.
Why does my BMI look healthy before adjustment?+
Removing a limb lowers scale weight but not height, so standard BMI falls even though body fat may not have changed. The adjustment restores a fair comparison with the usual BMI cut-offs, which is important because weight gain after amputation is common.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.