Ostomy Uncovered – How to Resize Your Baseplate

Disclaimer: This information is based on my own research into this particular aspect of stoma care as well as some personal experience and should not be used as medical advice or a diagnostic tool. The suggestions given within are taken from sources laid out in the references header.  If you seek advice regarding the things you experience within your own disease, please contact your SCN  for medical advice.

If you are looking for the entire ‘Ostomy Uncovered‘ series, you can find them all here.

Why is this important?

When you have your stoma formed, it will be a size which is unique to you and your own body. There can be rough guidelines for sizes when it comes to types of stoma – because of where they are formed in the digestive trace – but there is a lot of variation.

After surgery, a stoma will be large and swollen due to the bowel not function straight away and the effects drugs and being handled can have on it. This will go down in the weeks post op, and once settled it will become more consistant.

At first, a SCN will cut your bags for you, or show you how to make adjustments at home by yourself. They will not discharge you from their care after your operation until you can do a cut and change by yourself competently.

NB: It’s important to note that for those with a colostomy, they will have less change in their stoma size due to it being less active. For those with an ileostomy, they may experience more fluctuation with their size and shape from time to time, which is why being able to resize your bag at home is a good skill to learn how to do.

Step by Step Guide

I’ve never written about the whole process of how to size a new bag, it has been abit of trial and error but you soon pick it up. You learn where your stoma needs abit more room to expand and contract without leaving too much skin exposed. Im going to try and be as general as possible, but full disclosure – I use a Coloplast Sensura Mio Convex, for reference.

NB – most boxes of stoma bags will come with a cutting guide – a large leaflet which had different sizes of circles on them with markings in millimeters on them. They are there to help you get a general diameter size for your own stoma.

  1. Gather your supplies. This will at least be your new pouch, stoma scissors – with a curved edge and tip to avoid perforating your bag – and a pen.
  2. Remove your current bag and clean the skin and stoma, disposing of all the waste.
  3. Using the stoma guide from the box and a mirror, find the most appropriate circle size for your stoma. NB: this will be a circle in which the least amount of peristomal skin is visible.
  4. It is important at this point it is not too tight. You can check this by removing it from your skin and if it gotten wet or feels moist, it has touch the stoma is too tight / small. You want it to be snug but with a 1mm gap.
  5. If you find that it’s only a small section that has been moistened, you can remove it on the paper with your scissors and reapply, to check the fit.
  6. Repeat as necessary until happy with size and shape.
  7. NB: the step above takes the longest to get right. But please don’t be disheartened if it takes you a couple attempts. It is tricky, no doubt. It is a different angle and position compared to when your SCN does it.
  8. Once happy, you can then trace this size on to your actual bag! On the plastic backing to your baseplate, there will be a ‘size guide’ – which is technically used to show what range of cutting can be achieved on X, Y or Z bag. This varies from manufacturer to manufacturer and no two are the same. I will discuss how to resize a template between brands in the notes!
  9. Cut out the size you have created. You can check this is perfect by removing the plastic backing and placing it like you did the paper template, onto your skin. You can tweak it from here. NB: remember if you do tweak, do the same to your bag! It’s easy to forget, trust me!
  10. Apply your bag as normal, as per your routine.
  11. Keep the plastic backing as a template for your next change. I usually date mine, and sometimes add the type of bag – light, soft, deep, two or one piece etc – so I use the correct one.


  • Always use curved stoma scissors to cut your bags. The curve allows the cutting to not damaged the bags internal structures. You might accidentally pop the bag in the front and cause a leak.
  • For those people who have a stable stoma size, they can have their bags cut by the dispensing appliance company, free of charge. Usually this is for colostomies who use multiple closed pouches a day – cutting those would be an never ending task – or those with dexterity problems in their hands.
  • When it comes to ordering bags, do be mindful of the cutting range you have within them. These are usually displaced after the title of the product. Many companies will have multiple cutting ranges and variations to accommodate many sizes of stomas. If you are ever confused or unsure of which one suits you best, do get in contact with them; they know the products v well and can recommend the right size for you.
  • That being said, knowing your own size and shape is important too!
  • There are three types of stoma shapes: a) Circular – which is the same size all the way around. b) Elipse – which is measured left to right and top to bottom, meaning it had two measurements and sits as an oval. c) Custom – which is for stoma which do not fit into the two types above. These are usually done by SCNs and reviewed on a regular basis.
  • For trying bags across brands – using the template from one bag brand to another can sometimes work but other times does not! Using the sizing range on the bags is a good way to judge where your own stoma falls, but also knowing your size is helpful here too! The two combined, means you can do a very good measure by using common sense and your own eyes as guides.
  • Cutting your bag will become second nature. You will get into a natural rhythm and it’ll just flow like anything else you do on a regular basis. Sometimes you might make mistakes, but correcting it is pretty easy to do.

My Experience

I have never written about sizing my stoma bag alone before. However, I have written about my experiences on changing – once when I was quite new to it and one more recently when I had a new routine. You can read them here and here.

I do regularly check and update my template, as and when needed. I’ve found that I’ve kept alot of my templates over the years since my surgery and it’s weird and cool to look back and how my stoma has changed; with surgeries, medications, and general weight gain and loss.

Resizing my own bag was the one thing I really found difficult after surgery. I would wait until I saw my SCN for her to do this for me, and in turn ended up with v sore skin from an ill-fitting bag. Once we built up my confidence to do this at home alone, we would communicate via email to ensure things were good and soon I was doing it all myself.

Do you have any questions or queries? Or just want to share your own experiences? You can leave me a reply here or leave comments via my social media accounts – on
Twitter, find my blog page on Facebook and over on Instagram

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If you enjoyed this post check out IBD v IBS – Why Do So Many Get Misdiagnosed , The Liver & IBD and The What & Why: Dehydration

Further Reading:


  • Douglass Clawson

    08/07/2020 at 18:33

    How about the moldable wafer?

    1. Admin

      09/07/2020 at 10:15

      I would imagine it would a very similar process. It might involved using the cutting guide provided in the box and sizing against the skin directly. Hope that helps!

  • Ostomy Glossary •

    11/01/2021 at 20:36

    […] Template – The guideline to help mark out the size and shape of stoma you need to cut your bag to. For my handy guide, you can read more here. […]

  • Stoma Life – YEAR FOUR •

    31/03/2021 at 10:06

    […] Ostomy Uncovered – How to Resize your Baseplate – 07.04.20 […]

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