Bra Size Calculator
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UK Bra Size Calculator – Calculate Your Cup Size & Band Size
Use our UK Bra Size Calculator to calculate your starting bra size from your underbust and bust measurements.
Once you have your result, compare brands using our Bra Size Converter, check fit using our Bra Fitting Advice, and explore the full sequence in our UK Bra Cup Size Chart.
How to Calculate Your Bra Size
To calculate your bra size, measure your underbust and your fullest bust. The calculator uses your underbust measurement to estimate your band size, then compares your bust measurement to that band size to work out your cup size.
Bra Size Calculator Example
This example shows how the calculator uses your measurements to estimate a starting UK bra size.
A 30 inch underbust gives a starting 34 band size. A 41 inch bust creates a 7 inch difference, which gives an F cup. The calculator result is therefore 34F.
- 1 inch difference = A cup
- 2 inch difference = B cup
- 3 inch difference = C cup
- 4 inch difference = D cup
- 5 inch difference = DD cup
- 6 inch difference = E cup
- 7 inch difference = F cup
- 8 inch difference = FF cup
- 9 inch difference = G cup
- 10 inch difference = GG cup
If you want to understand how cup sizes progress beyond this, see our Double Cup Bra Sizes Explained guide and our UK Bra Cup Size Chart.
UK Cup Size Progression Example
Each UK cup size represents roughly a one-inch increase between the band size and the fullest bust measurement. The diagrams below show how cup volume increases from F to FF to G while the band size remains the same.
These simplified diagrams show how cup volume increases as you move through the UK cup size sequence.
UK Cup Size Progression Example
Each UK cup size represents roughly a one-inch increase between the band size and the fullest bust measurement. The diagrams below show how cup volume increases from F to FF to G while the band size remains the same.
These simplified diagrams show how cup volume increases as you move through the UK cup size sequence.
Bra Size Calculator Example
This example shows how the calculator uses your measurements to estimate a starting UK bra size.
A 30 inch underbust gives a starting 34 band size using the traditional UK fitting method. A 41 inch bust creates a 7 inch difference, which gives an F cup. The calculator result is therefore 34F.
How to Use the Bra Size Calculator
- Select your underbust measurement: Choose the size closest to your underbust from the dropdown.
- Select your bust measurement: Pick the size closest to your fullest bust measurement.
- Click Calculate: The calculator will show your UK band and cup size.
- Use the result as a starting point: Bra sizing is only a guide, so the final fit should always be adjusted by how the bra feels when worn.
After calculating your size, you can compare brands with our Bra Size Converter and troubleshoot fit issues in our Bra Fitting Advice.
This bra size calculator gives you a starting size based on traditional UK fitting measurements. The best fit is always confirmed by how the bra feels when worn.
If the band rides up, try a smaller band size. If the cups feel too tight or too loose, adjust the cup size accordingly. Small changes can make a big difference to comfort and support.
Related Bra Size Guides
Once you have your calculator result, these guides can help you understand your size in more detail:
Explore How Big Different Cup Sizes Are
If you want to understand how your cup size compares, these guides explain how different UK cup sizes look, how they scale across band sizes, and how volume changes:
Bra Size Calculator FAQs
Q: How do I use the Bra Size Calculator?
A: Select your underbust and bust measurements, then click “Calculate” to see your UK band and cup size.
Q: Is the result exact?
A: No. The result is a starting point based on your measurements. Final fit should always be adjusted by how the bra feels when worn.
Q: What if the band rides up or feels loose?
A: Try a smaller band size. If needed, adjust the cup size as well to keep the overall fit balanced.
Q: Can I compare my size across UK brands?
A: Yes. Use our
Bra Size Converter
to compare your result across different brands.
For general background on UK bra sizing systems and cup progression, see the bra size reference on Wikipedia .