Enter the underbust and overbust measurements into the calculator to determine the bust size. This calculator can also evaluate any of the variables given the others are known.

Bust Size Formula

The following formula is used to calculate the bust size.

BS = (UB + OB) / 2


  • BS is the bust size (inches)
  • UB is the underbust measurement (inches)
  • OB is the overbust measurement (inches)

To calculate the bust size, add the underbust measurement to the overbust measurement, then divide the result by 2. This will give you the average bust size.

What is a Bust Size?

Bust size refers to the measurement around the fullest part of a woman’s breasts and around her back. It is typically measured in inches or centimeters and is often used in determining clothing sizes, particularly for bras and other upper body garments. The bust size is not the same as the bra size, which also takes into account the measurement under the bust.

How to Calculate Bust Size?

The following steps outline how to calculate the Bust Size using the given formula:

  1. First, determine the underbust measurement (UB) in inches.
  2. Next, determine the overbust measurement (OB) in inches.
  3. Add the underbust measurement (UB) and the overbust measurement (OB) together.
  4. Divide the sum by 2.
  5. Finally, calculate the Bust Size (BS).
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge:

Underbust measurement (UB) = 30 inches

Overbust measurement (OB) = 36 inches