The Math Behind Sizing

Inches to Cup Size

Your cup size is simply the difference in inches between your band (underbust) and your bust measurement. Here is exactly how to calculate it.

Try the Auto-Calculator

Difference Between Band and Bust Size

To find your UK cup size, subtract your band measurement (in inches) from your full bust measurement (in inches). The resulting number corresponds to a cup letter.

Difference (Inches)UK Cup Size
0 inchesAA
1 inchA
2 inchesB
3 inchesC
4 inchesD
5 inchesDD
6 inchesE
7 inchesF
8 inchesFF
9 inchesG
10 inchesGG
11 inchesH
12 inchesHH
13 inchesJ

Example Calculation

Let's say you measured yourself using a soft tape measure:

  • 1
    Your Band Size = 34 inches
  • 2
    Your Bust Size = 38 inches
  • =
    38 - 34 = 4 inches difference

Looking at the chart above, a 4-inch difference means a D cup. Therefore, your size is a 34D.

Frequently Asked Questions

What cup size is a 5 inch difference?+

A 5-inch difference between your band and bust corresponds to a DD cup in UK sizing.

What cup size is a 3 inch difference?+

A 3-inch difference is a C cup.

What if my difference is a half inch? (e.g. 4.5 inches)+

If your measurement falls between whole inches, it's best to try the larger cup size first (e.g. size up to the 5-inch difference, which is a DD), or try the sister size.

Is this the same for US sizing?+

Up to 4 inches (D cup), yes. But at a 5-inch difference, UK sizing uses DD, while some US brands might use DD or E. A 6-inch difference is an E in the UK, but a DDD or F in the US.