Measuring your bra size

Measuring your bra size

Did you know, according to Marks & Spencer* 80% of women are wearing the wrong bra size? Not sure if you’re wearing the right size? This is our guide on exactly how to correctly measure yourself, to find your Runderwear size. 



If you’re experiencing any of the following, it’s likely your bra is not fitting correctly: 

  • Chafing – this is when the bra is rubbing against your skin causing discomfort 

  • The underband is too big and is not sitting snug to the skin 

  • Your breasts are not fully encased within the cups- potentially giving you ‘side-boob’ or ‘over-boob’ 

  • The underwire is digging in to your skin 

  • There is excess of cup fabric which may be creasing, wrinkling or dimpling 

  • Your breasts are not filling the cup 

If you experience any of the above problems, or you are new to Runderwear bras, then you’re in the right place! Keep on reading! 


Before we start here are some top tips to get the right fit: 

  • Use a flexible tape measure, not your retractable DIY version! 
  • Have a mirror nearby
  • Measure yourself braless or in a non-padded bra


  1. Always measure your underband first. Place the tape measure directly under your bust, measuring in inches, and ensure the tape measure is flat and level the whole way round the torso (check this in a mirror). Pull the tape measure tight and round to the nearest whole number. 

  2. Now measure your overbust. Place the tape measure around the fullest part of your breasts. Once again measure in inches and ensure the tape measure is flat and level the whole way round. Once again, pull the tape measure tight and round to the nearest whole number. 

  3. We use the plus 4 method, this means you need to add 4 inches to you underband measurement. So for example, if you have measured at 30”, your underbust size would become 34, 34 would become 38, and so on. So that is now your Runderwear underband size. 

  4. Now you need to calculate your cup. This is the difference between your underband and overbust measurements. To find your cup size subtract the underband measurement away from the overbust measurement. A difference of 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, 5 inches = DD and so on. So, for example, if you got an underband measurement of 28 and an overbust of 32, your cup size would be a D. 

  5. And finally, you simply put the two parts together, for example if your underband measurement was 28, that means the underband size would be 32, and if your overbust was 33, that means that your cup size would be a DD. This would make you a size 32DD. 

It's important to remember that different brands use different sizing methods so it's unlikely you will be the same size across multiple brands.

The most important thing is to ensure your sports bra is well fitted, supportive and comfortable, and that you measure using the correct measuring technique recommended by the manufacturer you are shopping with. 

For further sizing advice visit the Bra Size Finder at Runderwear or contact our Bra Specialist Molly on  



Reading next

Our essential guide to skin protection for runners
What makes a good sports bra?

Leave a comment

All comments are moderated before being published.

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.