Formula

IBW
Estimated ideal body weight in (kg)
Males: IBW = 50 kg + 2.3 kg for each inch over 5 feet.
Females: IBW = 45.5 kg + 2.3 kg for each inch over 5 feet.

ABW
Estimated adjusted body weight (kg)
If the actual body weight is greater than 30% of the calculated IBW, calculate the adjusted body weight (ABW):
ABW = IBW + 0.4(actual weight - IBW)

The IBW and ABW are used to calculate medication dosages when the patient is obese.

This formula only applies to persons 60 inches (152 cm) or taller.  If calculating by hand use formula as shown (inches & kilograms).  Formulas referenced from GlobalRPH.

Examples

Example 1

Calculate the ideal body weight (IBW) of a man who is 64 inches tall and weighs 70 kilograms.  If this man is obese (> IBW + 30%), calculate the adjusted body weight.

To solve the example using the calculator, select the radio button for male. Next, enter the height (inches)  and weight (kilograms):

weight = 70 kg
height = 64 inches
IBW = 59.2

Or solve using formula:

IBW = 50 kg + 2.3 x each inch over 5 feet (60inches)
IBW = 50 kg + 2.3 x 4 inches
IBW = 50 kg + 9.2
IBW = 59.2 kg

The man's actual weight is less than IBW + 30% so it is not necessary to calculate the adjusted body weight (ABW).

Example 2

Calculate the ideal body weight (IBW) of a woman who is 64 inches tall and weighs 80 kilograms.  If this woman is obese (> IBW + 30%), calculate the adjusted body weight.

To solve the example using the calculator, select the radio button for female. Next, enter the height (inches)  and weight (kilograms):

weight = 80 kg
height = 64 inches
IBW = 54.7

Or solve using formula:

IBW = 45.5 kg + 2.3 x each inch over 5 feet (60inches)
IBW = 45.5 kg + 2.3 x 4 inches
IBW = 45.5 kg + 9.2
IBW = 54.7 kg

The woman's actual weight is greater than the IBW + 30%, so calculate the ABW:

ABW = 54.7 kg + 0.4( 80kg - 54.7 kg)
ABW = 54.7 kg + 0.4( 25.3 kg )
ABW = 54.7 kg + 10.1kg
ABW = 64.8 kg

Note: