On this page
The adjusted BMI formula
Estimated full weight = current weight ÷ (1 − missing percentage ÷ 100)
Adjusted BMI = estimated full weight (kg) ÷ height (m)²
Use your full standing height from before the amputation, or a measured or estimated height. If height can't be measured, see BMI without a height measurement.
How much each limb segment weighs
These are average shares of total body weight, from studies of body segment weights:1
| Segment | Share of body weight |
|---|---|
| Hand | 0.7% |
| Forearm and hand (below the elbow) | 2.3% |
| Entire arm | 5.0% |
| Foot | 1.5% |
| Lower leg and foot (below the knee) | 5.9% |
| Entire leg | 16.0% |
For more than one amputation, add the percentages together.1
Worked example
A person who is 175 cm tall weighs 70 kg after a below-knee amputation:
- Missing share: 5.9% (lower leg and foot).
- Estimated full weight: 70 ÷ (1 − 0.059) = 70 ÷ 0.941 = 74.4 kg.
- Height squared: 1.75 × 1.75 = 3.0625.
- Adjusted BMI: 74.4 ÷ 3.0625 = 24.3.
Without the adjustment, BMI would be 70 ÷ 3.0625 = 22.9, which understates it by 1.4.
Things to keep in mind
- Prosthetics. Weigh yourself without your prosthesis, or subtract its weight.
- Segment shares are averages. Your actual limb weight may differ, especially for partial-segment amputations. Use the closest row.
- Muscle changes. Muscle in the remaining limb often decreases after amputation, which BMI can't show.
Talk to a dietitian or doctor if you're not sure which row fits your amputation, for example a partial-segment or above-knee amputation. They can make a more precise estimate and assess weight and nutrition after limb loss.
Frequently asked questions
Why does BMI need adjusting after an amputation?
BMI compares weight to height. Losing a limb lowers weight without lowering height, so the standard calculation makes BMI look lower than it is for the body's actual build.
What if I had an above-knee amputation?
Use "Entire leg" (16.0%) for an amputation through or near the hip. For one partway down the thigh, the true share is somewhat less. A dietitian can make a more precise estimate.
Do the same categories apply?
Yes. Adjusted BMI is compared with the standard adult categories. BMI categories.
Sources
This page is for education and is not medical advice. A dietitian or doctor can assess weight and nutrition after limb loss.
