How to Measure Your Stoma: Ostomy Tips

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A crucial skill that anyone with an ostomy should know is how to measure their stoma. Not only does it help to prevent leaks, but it can help to extend appliance wear time, and save your skin!

This guide will explain what supplies you’ll need, as well as show you how to properly measure your stoma and cut your wafer.

** If you are a new ostomate then it’s very often recommended that you measure your stoma with every appliance change for at least the first month to six weeks. That’s because your stoma will be shrinking during that time.


Who This Guide is For

Ostomates who will benefit the most from this guide are ones who have an uncomplicated, round-ish stoma that is slightly protruded.

The process is very similar for ileostomates, colostomates, and urostomates who use cut-to-fit appliances.

If you have a recessed, flushed, or prolapsed stoma, then you may not get perfect results by following this guide.

Things to Note

You would think that putting together a guide on how to measure a stoma would be pretty straight forward.  Unfortunately, there are a few things that make this difficult:

Loop vs. End Ostomy

Due to the “double-barrel” nature of a loop ostomy, it may not be possible to measure the stoma using a circular guide.

If you have a loop ostomy, you may need to be creative about how you measure your stoma. One suggestion is to use a half circle, rather than the full circle of the measuring guide and measure each part (or each half)  of your stoma separately.  You can then trace that onto your wafer.

Every Wafer is Different

Not all wafers will act the same when they are worn.  While all wafers tend to swell a bit as they come in contact with fluids or output, the degree in which they swell can differ from brand to brand.

Ostomy wafer swelling
Notice how puffy the edge of the wafer got? That’s why leaving a little gap is OK.

Because of this, you may need to cut your wafer slightly larger to accommodate the expansion. Doing this also helps to prevent the wafer from “strangulating” your stoma by putting too much pressure around it.

Another thing about wafers is that they come in all kinds of sizes and materials. When I buy wafers, I try to get a size that allows for about 10cm of space between my stoma and the edge of the cutting lines (or up to the flange ring on my 2pc system).

If you use a wafer that doesn’t give you enough space, you may end up having difficulties cutting it, or worse, develop leaks.

There’s no harm in getting a wafer that larger than you need, and you may be able to get more pouch support because it has more surface area to stick to.

That is, of course, provided that a large wafer fits well on your skin (there is such thing as having a wafer on that’s too big!).

Stomas Can Change

As our bodies change and so do our stomas.

It’s expected that your stoma will change its size (get smaller) for the first four to six weeks after surgery due to the swelling that occurs post-op.

Likewise, weight loss/gain can change the size and shape of your stoma, and so can things like a prolapsed stoma or a hernia.

My stoma fluctuates between 28mm and 32mm at various times, despite being over three years out from surgery. Stuff like this happens!

While you won’t able to control or predict these changes, you can make sure that your wafer is cut as accurately as possible.

For more information on why stomas can change their size or shape, please refer to THIS article.

What You’ll Need

Measuring stoma supplies needed
Basic items needed to measure your stoma.

These are the supplies I like to keep on hand, but depending on the appliance you’re using, some of these won’t be necessary.

  • Stoma measuring guide. If you’re using a cut-to-fit wafer, these will almost always come in the box of wafers.
  • Ostomy wafer scissors (don’t use regular scissors, cuticle scissors, or anything with a sharp tip). I use and recommend THESE (Amazon affiliate link).
  • Pen or marker for tracing.
  • Your wafer (obviously!).
  • Gauze (optional) to dry your stoma. I prefer gauze over toilet paper/paper towel because the latter tend to break apart when wet.
  • Mirror (optional, but recommended). This can help to see under your stoma while measuring it.

Some wafers will come with cutting lines printed on the back, while others do not. If your stoma is a consistent size, feel free to cut the wafer according to the cutting lines without the need to measure and trace the hole.

Ostomy wafers cutting lines
Not all wafers will have cutting guides printed on the back – be careful not to make the hole too big on the ones that don’t.

Steps to Measuring Your Stoma

  • Gather your necessary supplies.
  • Empty your bag and wash your hands.
  • Remove your previous wafer then shave, clean, and dry the skin around your stoma.
    Clean and shave skin around stoma
    Start with clean, hair-free skin.
  • Take your stoma measuring guide and find the approximate size of your stoma or use the previous measurement.
    Find your stoma size
    Find a size that’s close to what you’ll need.
  • Place the guide over your stoma so that your stoma goes through the hole.
    Stoma measuring guide around stoma
    Your stoma may bleed when scratched by the measuring guide. Don’t panic – it’s normal.
  • You’ll want to make sure that there’s about a 1/16 – 1/8″ (approx. 1.5 – 3mm) gap between your stoma and the edge of the hole. Remember, as wafers do swell, you may need to adjust this gap accordingly. If you are using a barrier ring or similar product, it’s ok to cut the hole slightly larger (but not too much!).
    Measuring stoma how much gap compare
    Leave a tiny bit of space between your stoma and the edge of the hole you’ve cut.
  • After finding the right size, place the measuring guide on the backside of your wafer with the hole in the center of the wafer. In certain situations, like when you’ve got surgical wounds or skin problems, you may need to place the hole off-center. If you do this, just be sure that you are still cutting the hole within the boundaries of the “maximum cut” ring.
    cutting wafer offcenter
    If you do have to shift your hole remember not to cut past the outer ring.
  • Trace the hole on your wafer using a pen or marker.
    Ostomy wafer trace hole
    Use a marker or pen to trace the hole.
  • Cut out the hole using ostomy wafer scissors. If you are using a one-piece appliance, blow into the bag first to give some space for your scissors to move.
    Cutting your ostomy wafer
    A pair of good ostomy scissors can make this part really easy.
  • Test the size of the cutout by placing it over your stoma before you remove the plastic liner on the back of your wafer. Be careful as the edge of that hole may be sharp while the plastic backing is still on.
    Test your wafer before applying
    Before removing the back liner to your wafer, make sure to test it once last time and adjust the hole if necessary.
  • Make any adjustments if required.
  • Complete any other skin routine, including putting on a barrier ring, ostomy paste, ostomy powder, barrier wipes, etc.
  • Apply your wafer.
Tip: Keep the plastic liner from your wafer and use it as a template for your next appliance change. If your stoma stays consistent then it will be easier to use compared to the paper measuring guides.

Use your old wafer lining the next time

You can use your old release backing as a new template, but test it around your stoma to make sure it’s still the ideal size.

Final Words

I hope that this guide has given you some insight on how to measure and cut the hole for your stoma.

Feel free to make small adjustments to these steps in order to accommodate your particular needs.

Question: Do you have any tips to share about measuring your stoma?
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1 year ago

I suggested a while back to someone having trouble measuring a difficult stoma shape that they take a piece of paper, or even wax paper, or parchment paper. Trace on a circle from your wafer for size, with a ruler, run lines thru it to make uncut wedges. Then with a sharp scissors or knife cut thru the straight lines. Then you have what looks like a pie cut in wedges. Place the paper over your stoma and then fold back the wedges to the how ever close you want it to the edges of your skin and stoma. Do not make it too small, you can cause swelling and even bleeding. Check the fit with a mirror  and then carefully trace it onto another piece of paper, cut it try it onto your tummy, and then trace onto your wafer., if the fit is good, you can use the plastic as Eric said for a guide to measure again. I hope this works for you.On healing the skin, it is always wise to check with your doctor to make sure whatever is going on does not need an antibiotic or a fungal cream. A fungus can be hard to clear up and needs a prescription. But if you caught a rash quickly from a leak, it will tingle mostly or burn. For myself, I have used the stoma powder, but I have also used some Penetin Baby diaper cream. However, I used  q-tips and ran it between my finger to tighten the cotton, and then used a tiny bit to place on the areas hurting and then the stoma powder on top of that, and then the wafer. The cream can be hard to remove so use sparingly, it stopped further moisture from burning my skin and the stoma powder also absorbed further moisture. I had a rash so bad one day week that I replaced my one piece bag up to three times a day. The rash was oozy of clear moisture and hurt badly. I could hardly move. So, I changed the pouch often for about two days and then was able to lessen it daily as it healed. I have sensitive skin and eczema, but doing it this way helped a lot.  I would also place a wet, but frozen cloth over the pouch after changing to cool the skin, protect the stoma with another cloth. I had been gardening and bent once too often and did not feel the rash taking place so this is what I got. It took a good week for the area to heal again, and not had a rash since thank Heaven. This is not what Eric or his site recommends. The experience was hit and miss. 

1 year ago

What happens when you cut the hole to big..

1 year ago

Hi Folks, Was having a think about this problem, and what could be SAFELY put round the stoma to then trace an image. One item I have thought of is a “pipe cleaner” these are bendable covered in cotton and would hold shape. Am thinking that fed round the stoma and used to make the shape. this could then to traced on the wafer. These are sold now a days for craft work in packs. Have to say ALWAYS be careful what goes near the stoma.

Tod Thompson
1 year ago

Any tips on measuring a stoma that is not round? Mine is oval, about 40mm wide and 25mm in height?

Jess Thomson
2 years ago

HI: I Found this blog the best yet maybe because I could relate to it. I have a urostomy and use Hollister bags, when first having my bladder removed over 4 years ago I talked with a guy who had both, he suggested each time I opened my box of 10 to cut them all to the required size of course leaving the transparent backing on, I also put the tape on, this means when my bag needs changing every 2nd day I only have to remove the backing and tape. As a box only contains 10 bags my stoma size does not change during this time. Originally it took me an hour to cut all the bags now I am down to 45 minutes..
Not sure if this is a help to anyone else with different ostomies.
Regards Jess

Jamie baker
Jamie baker
2 years ago

I am a new colostomy patient. I swallowed a toothpick (Yup that’s right) and caused infection. I am fortunate mine is temporary. I habe had it a month now. I just recently started experiencing under my stoma a raw, burning feeling that itches and hurts. Any advice? Maybe my wafer is cut too big? Thanks!

2 years ago
Reply to  VeganOstomy

I found the Convatec  Natura sur-fit moldable flange to be ideal; I didn’t have to cut the stoma opening every time. It was pretty forgiving, too, and I could mold it back if I made the opening a little too big on it.  A real life-saver for me.

I so much appreciate your openness with your experiences; it has helped me tremendously.

2 years ago

Just a comment on the adhesive. Be careful of Holister brand because they use pectin in their adhesive so anyone allergic to apples, peaches, plums, ect. might react to their products. My skin blistered under the water and took some effort to heal.

2 years ago

Has anyone made a stoma measuring guide that you can clean? A box of ten bags comes with (paper) measuring guide, which of course gets dirty as soon as you use it once. I would GLADLY pay $5-$10 for a plastic one which I could re-use.

5 months ago
Reply to  VeganOstomy

I have a plastic one. I got it in the hospital from omnigon. They may sell them.

3 years ago

I’m a new ostomate, temporary ileostomy for cancer, post surgery a little over two weeks. I have been constantly reading and researching what’s out there that might streamline the process, but it’s still a frustrating learning curve, as what works one time might not work another. It has to get better! I’m having reaction to bag adhesive and have skin breakdown at the stoma site, so your information has been MOST helpful! Love the videos and I appreciate that you are freely sharing your experiences, as it lets me know that people live well with this and there’s a lot out there to try.Thanks!