The
Calculations Explained:
Individual
Weights:
The
Hamwi Formula:
Dr. G.J. Hamwi's formulas have become very popular since they first appeared
in a publication of the American Diabetes Association in 1964. Many of
the weight calculators on the web use this formula and aside from BMI
based calculations, this is probably the most popular method of calculating
ideal weight. It has an advantage over most other calculation methods
in that Dr. Hamwi suggests that the results may be reduced by 10% for
a person with a light frame, and increased by 10% for a person with a
heavy frame. Thus I provide all three numbers here. The formulas are:
Men: 106 lb for the first 5 ft; 6 lb for each inch over 5 ft
Women: 100 lb for the first 5 ft; 5 lb for each inch over 5 ft
The
Robinson Formula:
This
is similar to the Hamwi Formula but is based on a revision of Devine.
The formulas
are:
Men:
115 lb for the first 5 ft; 4 lb for each inch over 5 ft
Women: 108 lb for the first 5 ft; 3.75 lb for each inch over 5 ft
The
Miller
Formula:
This
is also derived from Devine. The formulas are:
Men: 124 lb for the first 5 ft; 3 lb for each inch over 5 ft
Women: 117 lb for the first 5 ft; 3 lb for each inch over 5 ft
BMI
Based Formula:
BMI
or Body Mass Index is the preferred method of calculating obesity for
most clinicians. This is the
method the US government pushes. It is based on a calculation
that supposedly takes into consideration the lean body mass and adds in
an appropriate amount of fat. For my calculations, I simply reversed the
process to arrive at an ideal weight based on an average BMI
of 23. Thus, instead of using your height and weight to calculate your
BMI, I use the height you input to provide a weight that would be equivalent
to a BMI of 23, a number towards the high end of normal. Note that BMI
does not take gender, age, body composition, or activity level into consideration
Average
Weights:
The first number is the mean average weight of the above calculated weights.
Because both Dr. Hamwi and the BMI allow for variation based on frame
size and other factors, the next result is a range based on 10% under
and 10% over the resulting average. Thus if you feel the average is too
low due to frame size or other factors, use the upper end of the normal
range. Likewise, if you think the weight listed for average is too high
based on your frame size or other factors, use the lower end of the range.
I have also included the range of weights considered to be "normal"
according to the BMI. This is included as a comparison to the average
range right above it. In general, the BMI range will be slightly larger
on both the upper and lower ends for women, meaning that it will have
a "lower" low and a "higher" high. For men, the average
weight will likely be significantly higher on the lower end than the BMI,
and slightly higher on the upper end.
Caloric
Need:
BMR = Basal Metabolic Rate  a number that represents your caloric
need before factoring in activity level.
TDEE =
Total Daily Energy Expenditure  This it the BMR times an energy multiplier
that is designed to account for how active you are. See below for the
formulas used.
Caloric
Need for Weight loss = (TDEE  500). This will give an average loss
of one pound a week as 500 X 7 days = 3500 calories, or the amount needed
to burn one pound of fat.
HarrisBenedict
Formula
The HarrisBenedict formula uses height, weight, age, and sex to determine
basal metabolic rate (BMR). The only variable it does not take into consideration
is lean body mass. Therefore, this equation will be accurate for many,
but will underestimate the caloric needs of muscular athletes and overestimate
the caloric needs of the obese.
Because
of this, I am actually using an average from the computed individual weights
and NOT total weight for this calculation. Thus will have a
tendency to slightly underestimate the caloric needs of the obese since
fat is not actually completely metabolically inert. Even so, I believe
this is a better measure than one based on total weight because in my
opinion it is generally better to err on the side of too few calories
than too many when discussing caloric need for the overweight.
For reference,
the formula used is as follows:
Men: BMR
= 66 + (6.23 X weight in pounds) + (12.7 X height in inches)  (6.8 X
age)
Women: BMR
= 655 + (4.35 X weight in pounds) + (4.7 X height in inches)  (4.7 X
age)
The calculations
for TDEE are identical to those used for the KatchMcArdle Formula on
the right.


Healthy
Body Fat Guidelines*:
Age

Women

Men

20
 39

21%  32%

8%
 19%

40
 59

23%
 33%

11%  21%

60
 79

24%
 35%

13%
 24%

*Adapted
from: Gallagher et al., "Healthy percentage
body fat ranges: an approach for developing guidelines based on body mass
index." American Journal of Clinical Nutrition, 72 (3): 694.
Weight
Results from % Body Fat:
This portion of the calculator will likely provide a more accurate
goal weight for many people. It works by first calculating lean body mass:
Lean Body Mass =
Your
Current Weight X (1  (Your Current Body Fat / 100))
Next,
two differing methods are used to calculate the results:
Method
1:
This method is called "lossy" because it purposely calculates
the desired body fat as a function of the lean body mass. Thus if you
were to check, you'd find that the Lean Body Mass dropped by 5 to 10%.
This method is included because some research suggests that overweight
people (especially the morbidly obese), tend to lose some muscle mass
as they lose weight. I have added this method to take this into consideraton.
It should not be considered any more, or any less accurate than method
2 below. The actual calculation method is as follows:
Ideal Weight =
(Lean Mass * (Desired Body Fat / 100) + Lean Mass)
Method
2:
This method is called lossless because it assumes that no muscle mass
will be lost during weight loss. This method has no formula associated
with it. Instead, it uses the power of the computer to quickly check
up to twohundred possible body weights till it finds one that fits the
desired percent body fat you entered. (If you care about why it must be
done this way, click here: 123fitnessandhealth).
Keep
in mind that if you got your percent body fat from BIA (Bioelectrical
Impedance Analysis), that either of these methods can be off by a few
percent. Some reports state that this is especially true for severely
obese individuals. The point is that even this method is not a 100% accurate
measure of true lean body mass and thus the results of this calculator
should not be considered perfect. It is highly dependent on how accurate
the body fat measurement was originally and whether or not the amount
of muscle mass changes during the course of weight loss.
Caloric
Need:
BMR
= Basal Metabolic Rate  a number that represents your caloric need
before factoring in activity level.
TDEE =
Total Daily Energy Expenditure  This it the BMR times an energy multiplier
that is designed to account for how active you are. See below for the
formulas used.
Caloric
Need for Weight loss = (TDEE  500). This will give an average loss
of one pound a week as 500 X 7 days = 3500 calories, or the amount needed
to burn one pound of fat.
KatchMcArdle
Formula
The
KatchMcArdle formula differs from the HarrisBenedict formula in that
KatchMcArdle takes lean body mass into consideration. This calculation
is therefore only possible if you know your percentage body fat.
Generally
speaking, this is a better measure of caloric need for the obese than
HarrisBenedict because it represents your actual body composition and
is not based of assumptions about what one "should" weigh.
The formula
is as follows:
BMR = 370 + (9.79759519 X Lean Mass in pounds)
TDEE is calculated
by multiplying your BMR by your activity multiplier from the list below:
 Sedentary
= BMR X 1.2 (little or no exercise, desk job)
 Lightly
active = BMR X 1.375 (light exercise/sports 13 days/wk)
 Mod.
active = BMR X 1.55 (moderate exercise/sports 35 days/wk)
 Very active
= BMR X 1.725 (hard exercise/sports 67 days/wk)
 Extr.
active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X
day training, i.e marathon, contest etc.)
Important
Note:
Regardless
of what the calculator tells you, going under about 10001200 calories
for a woman and 13001500 for a man can be detrimental to weight loss
as this can cause your body to try harder to retain weight by slowing
your metabolism. This is commonly called "starvation mode" and
is a natural reaction to too low a caloric intake. As such, do not go
lower than these numbers without the advice and consent for your physician.
If the calculator gives you numbers smaller than this, it is probably
because you are small in stature and not exercising much. If so, the best
advice I can give is to increase your activity level and this will allow
a more normal caloric intake.
