About Body Mass Index (BMI)

What is BMI?

Body Mass Index (BMI) is a common method for assessing weight status for adults. BMI is calculated using a person’s height and weight. Although it is not a direct measure of body fat, BMI is a reliable indicator of body composition for most people. Calculating a person’s BMI is inexpensive and easy to do. However, common BMI calculators are not appropriate for people with limb loss. These tools do not account for the estimated weight of the missing limb(s) for people with limb loss.

The Amputee Coalition and members of our Scientific and Medical Advisory Committee (SciMAC) created our BMI Calculator for People with Limb Loss to provide the limb loss community with an easy-to-use tool to assess their weight status. Until now, such tools have not been readily available to the limb loss community. Like the general population, being overweight or obese can negatively impact the health and well-being of amputees. We hope our tool will allow amputees to assess their weight status and take appropriate steps to achieve a healthy weight.

How is BMI used?

BMI is used as a tool to assess a person’s weight status and identify possible weight problems. BMI is not a diagnostic tool. You should talk to your healthcare provider if you receive a BMI score that is not within the normal range. Only your healthcare provider can determine if your weight status is a risk to your health.

How is BMI calculated?

BMI is calculated using the following formula:

For pounds and inches:
[Weight (lb)/height (in)2] x 703

For kilograms and meters:
Weight (kg)/[height (m)]2

For people with limb loss, the standard BMI formula must be adapted to account for the estimated weight of the missing limb. One possible method for calculating BMI for people with limb loss is as follows:

W0 = weight without prosthetic device (lb)
P = percentage of total body weight of missing limb (lb)
We = estimated body weight (lb)

Step 1 – Calculate estimated body weight
We= W0/(1-P)

Step 2 – Calculate estimated BMI
Estimated BMI = [estimated body weight (lb)/height (in)2] x 703
Estimated BMI = [We(lb)/height(in)2]  x 703
For P, we used the following estimates for percentage of total body mass for common amputation levels. These estimates were arrived at through a review of the literature on body segment mass estimates and discussions with researchers.

Amputation Level Estimated Percentage of Total Body Mass
Foot 1.30
Below-Knee 3.26
Above-Knee 9.96
Hip Disarticulation
Shoulder Disarticulation 5.00
Above-Elbow 3.55
Below-Elbow 1.45
Hand .70

How is BMI interpreted?
A person’s weight status is categorized using the following BMI ranges:

BMI Weight Status
Below 18.5 Underweight
18.5 – 24.9 Normal
25.0 – 29.9 Overweight
30.0 and Above Obese

If your BMI score is not in the “Normal” range, then you should talk to your healthcare provider. The Amputee Coalition has some resources available on our Web site to help amputees increase their physical activity level and develop healthy eating habits.

Our BMI calculator for amputees has not been validated against actual measures of body fat composition in amputees. Therefore, our calculator is an estimate of weight status for amputees and has the following limitations:

  • Appropriate tools to accurately assess weight in individuals with limb loss are not widely available. For example, many primary care offices do not possess a scale capable of weighing a person who uses a wheelchair. Using inappropriate equipment may lead to an inaccurate weight measurement.
  • Methods for assessing weight in individuals with limb loss are inconsistent. We recommend that you enter your body weight without your prosthesis or other assistive device. In order to obtain this measurement, a variety of methods are used, which may produce inconsistencies in determining the weight of a person with limb loss.
  • Accuracy of evaluating height in individuals with bilateral lower-limb amputations and congenital limb difference. A person’s height is an important part of calculating their BMI. Accurately assessing height may be difficult for individuals with bilateral lower-limb amputation or who have a congenital limb difference.