Use our UK Bra Size Calculator to calculate a starting bra size from your underbust and fullest bust measurements. Your result is shown in UK sizing, with equivalent sizes for US/Canada, Europe, France, Australia/New Zealand and Japan.
Once you have your result, use our Bra Size Converter for more international size comparisons, check fit using our Bra Fitting Advice, and explore the full UK cup sequence in our UK Bra Cup Size Chart.
Enter your underbust and bust measurements in inches to calculate a starting UK bra size. Your equivalent US/Canada, European, French, Australian/New Zealand and Japanese bra sizes will also be displayed with your result.
Want to compare your calculated size visually? Try our UK Bra Size Visual Comparison Tool to compare all 220 UK bra sizes using original illustrations.
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 with that band size to work out your cup size. It then displays equivalent international bra sizes based on the calculated UK result.
This calculator uses a traditional UK bra-sizing method. An even underbust measurement is increased by 4 inches and an odd underbust measurement by 5 inches to estimate the starting band size. The difference between that band size and the fullest bust measurement is then used to calculate the UK cup size.
Bra-sizing methods can vary, so the result should be treated as a starting size rather than a guaranteed fit. Use our Bra Fitting Advice to check the band, cups and overall fit once you try on a bra.
This example shows how the calculator uses your measurements to estimate a starting UK bra size. Once the UK size is calculated, the result also displays equivalent international bra sizes.
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 UK 34F.
The calculator then uses this UK 34F result to display its equivalent US/Canada, European, French, Australian/New Zealand and Japanese bra sizes.
The UK cup-size calculation used in this example follows this sequence:
If you want to understand how UK cup sizes progress beyond this, see our Double Cup Bra Sizes Explained guide and our UK Bra Cup Size Chart.
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.
After calculating your size, use our Bra Size Converter for more international size comparisons, and check fit issues using our Bra Fitting Advice.
This bra size calculator gives you a starting UK 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.
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Once you have your calculator result, these guides can help you understand your UK size, international equivalents and alternative sizes in more detail:
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 cup volume changes through the UK size sequence:
Q: How do I use the Bra Size Calculator?
A: Select your underbust and fullest bust measurements, then click “Calculate”. The calculator will show your starting UK band and cup size, followed by equivalent sizes for US/Canada, Europe, France, Australia/New Zealand and Japan.
Q: Does the calculator show international bra sizes?
A: Yes. The calculator first works out your UK bra size, then automatically displays the equivalent US/Canada, European, French, Australian/New Zealand and Japanese bra sizes. You can also use our
International Bra Size Converter
for more size comparisons.
Q: Is the calculator result exact?
A: No. The result is a starting point based on your measurements. Final fit should always be checked when the bra is 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. For more help, see our
Bra Fitting Advice.
Q: Can I compare my size across different bra brands?
A: Yes. Use our
Bra Size Converter
alongside individual brand size guides when comparing sizing systems and brands.
For general background on bra sizing systems and cup progression, see the bra size reference on Wikipedia .
