To measure a stoma, you place a measuring guide (included with most ostomy supplies) over the stoma and find the opening that fits closest around it without touching the stoma itself. For round stomas, this takes seconds. For oval or irregular shapes, you’ll need to trace the outline and measure the widest and tallest points separately. Getting the right measurement matters because it determines how well your pouching system fits and protects the surrounding skin.
What You Need to Measure
Most ostomy product boxes include a paper or plastic sizing guide with pre-cut circles in graduated sizes. This is your primary tool. If you don’t have one, you can download printable templates from most ostomy supply manufacturers, or your stoma care nurse can provide one. You’ll also want a pen, a piece of thin cardboard or stiff paper (a cereal box works well), and scissors for tracing irregular shapes.
A small mirror or your phone’s front camera can help you see the stoma clearly if it sits in a difficult spot on your abdomen.
Measuring a Round Stoma
Hold the sizing guide up to your stoma and try different openings until you find the one that fits closest around the base of the stoma without the edge pressing against the stoma tissue. The goal is roughly 1 to 2 millimeters of clearance between the edge of the opening and the stoma itself. Too tight and you risk cutting into the stoma. Too loose and exposed skin will contact output, leading to irritation and breakdown.
Always measure at the base where the stoma meets the skin, not at the tip. If your stoma protrudes significantly, the top may be a different width than the base, and it’s the base measurement that determines your pouch opening size.
Measuring an Oval or Irregular Stoma
Many stomas aren’t perfectly round. They can be oval, kidney-shaped, or slightly lopsided. For these shapes, a standard circular sizing guide won’t give you an accurate fit.
Instead, place a piece of thin cardboard or stiff paper over your stoma area. Gently feel for the edges of the stoma and trace its outline with a pen. Cut out the traced shape and hold it back up against your stoma to check the fit, adjusting as needed until you have a template that sits about 1 to 2 millimeters away from the stoma on all sides. You can then use this custom template to cut the opening on your pouching wafer each time.
For oval stomas specifically, some manufacturers sell oval sizing guides with pre-cut elliptical openings. These save time if your stoma is a consistent oval shape. When noting an oval stoma’s dimensions, record both the width (side to side) and the height (top to bottom) so you can communicate these measurements to a supplier or stoma nurse.
Measuring Stoma Height
The diameter of your stoma is only one measurement that matters. How far the stoma protrudes from your skin, its height, determines what type of wafer you need. An ideal stoma protrudes about 2 centimeters above skin level. You can estimate this by looking at the stoma from the side, ideally with a mirror, and comparing the protrusion to a ruler held alongside it.
Stomas fall into a few categories based on height. A “raised” stoma sits visibly above the skin surface. A “flush” stoma sits level with the skin. A “retracted” stoma actually dips below the surrounding skin level. Flush and retracted stomas often need a convex wafer, which has a curved surface that presses gently into the skin around the stoma to create a better seal. A raised stoma typically works fine with a standard flat wafer.
Some stomas also change height depending on position. A stoma might protrude normally when you’re standing but slide outward when you’re sitting, or vice versa. Check your stoma’s height while lying down, sitting, and standing to get a complete picture. If the height varies significantly between positions, let your stoma nurse know, because it affects which products will seal reliably throughout your day.
How Often to Re-Measure
Your stoma will change size considerably during the first two to three months after surgery. The post-surgical swelling gradually resolves, and the stoma shrinks as it heals. During this period, measure your stoma before every pouch change, or at minimum weekly. Using a pouch opening sized for a swollen stoma on a stoma that has since shrunk leaves too much exposed skin and invites irritation.
After about three months, most stomas reach a stable size. At that point, you can measure less frequently, but it’s still worth checking every month or two. Weight gain, weight loss, pregnancy, hernias near the stoma site, and normal aging can all shift the size or shape over time. If you notice your pouch seal isn’t holding as well as it used to, re-measuring is always a good first step before assuming the product is the problem.
Translating Your Measurement to Product Size
Once you have your stoma’s dimensions, you’ll use them to select either a pre-cut or cut-to-fit wafer. Pre-cut wafers come with a fixed opening size and work well for round stomas that have reached a stable size. Cut-to-fit wafers have a starter hole that you enlarge yourself using your measurement or template, which gives you flexibility for irregular shapes or stomas that are still changing.
If your stoma falls between two pre-cut sizes, choose the larger one. A slightly larger opening with a small amount of exposed skin is safer than an opening that’s too tight and rubs against the stoma. You can protect any small gap of exposed skin with a barrier ring or paste.
Keep a written record of your measurements with dates. This log helps you and your stoma care nurse spot trends, like gradual shrinkage or a shape change that might call for a different product. It also saves time when reordering supplies, since you’ll know exactly what size to request without re-measuring from scratch.