Basics
How to Measure Your Stoma Correctly
Learn how to measure your stoma accurately for a secure, leak-free appliance fit. Step-by-step guidance for colostomy, ileostomy, and urostomy care.
On this page
- Why Accurate Measurement Matters
- When to Measure
- In the Early Post-Operative Period
- Once the Stoma Has Stabilised
- What You Will Need
- Step-by-Step: How to Measure Your Stoma
- Step 1 — Empty and Clean the Area
- Step 2 — Observe the Shape
- Step 3 — Measure Width and Height
- Step 4 — Create or Update Your Template
- Step 5 — Transfer the Template to the Baseplate
- Step 6 — Check the Fit
- Special Situations
- Flush or Retracted Stomas
- Mucocutaneous Separation or Irregular Edges
- The Bottom Line
Measuring your stoma correctly means recording its width, height, and shape so that the aperture in your baseplate or one-piece appliance fits snugly around — but not tightly over — the stoma. A well-fitted opening protects the surrounding skin, prevents leakage, and reduces the risk of appliance failure. The process takes only a few minutes and should be repeated regularly, especially in the weeks after surgery.
Why Accurate Measurement Matters
The baseplate aperture acts as the primary barrier between your stoma output and your peristomal skin. If the opening is too small, it can press against the stoma tissue and potentially impair circulation or cause trauma. If it is too large, output can pool on exposed skin and cause irritation, inflammation, and breakdown — a condition sometimes called peristomal moisture-associated skin damage.
A correctly sized aperture typically leaves no more than 1–3 mm of clearance between the edge of the cut hole and the base of the stoma. This small margin accommodates natural movement and slight fluctuations in stoma size without leaving skin unprotected.
When to Measure
In the Early Post-Operative Period
A newly formed stoma is almost always oedematous (swollen) immediately after surgery. Over the following six to eight weeks, swelling resolves and the stoma reduces — sometimes considerably — to its resting size. During this period, measure at every appliance change and adjust your cut accordingly. Do not assume the size you were discharged with will remain correct throughout your recovery.
Once the Stoma Has Stabilised
After your stoma has reached a stable size — usually confirmed by your stoma care nurse at a follow-up appointment — re-measure every one to three months as a routine check, and promptly if you notice leakage, skin soreness, or a visible change in stoma appearance. Factors such as substantial weight change, abdominal herniation near the stoma, or certain medications can alter the size or profile of a previously stable stoma.
What You Will Need
- A measuring guide or stoma template card (usually included with your appliance supplies)
- A soft tape measure or ruler with millimetre markings
- A pen or soft pencil
- A mirror (optional but helpful for self-inspection)
- Good lighting
If you do not have a purpose-made template card, plain paper or thin card works well as a substitute.
Step-by-Step: How to Measure Your Stoma
Step 1 — Empty and Clean the Area
Begin with an empty pouch. Remove the old appliance carefully, peel any adhesive residue away gently, and clean the peristomal skin with warm water. Allow the skin and stoma to dry fully before measuring, as moisture can distort soft tissue.
Step 2 — Observe the Shape
Look at your stoma in good light, ideally at eye level with the help of a mirror. Note whether it is:
- Round (circular in all directions)
- Oval (longer in one axis than the other)
- Irregular or asymmetric (kidney-shaped, D-shaped, or lobulated)
Shape matters because the cut in your baseplate must follow the actual contour of the stoma base, not an assumed circle.
Step 3 — Measure Width and Height
Using your ruler or the measurement guide:
- Measure the widest horizontal diameter (side to side) in millimetres.
- Measure the longest vertical diameter (top to bottom) in millimetres.
For a round stoma these two figures will be similar. For oval or irregular stomas, record both separately. If using a template card, you can hold it gently against the stoma and identify which pre-printed circle or oval most closely matches — but hand-tracing (Step 4) is generally more reliable for non-circular shapes.
Step 4 — Create or Update Your Template
Place your template card or paper against your abdomen next to the stoma and trace around the base of the stoma with a pen, following the actual edge of the mucosal tissue where it meets the skin. Cut out the traced shape carefully. This is your personal template for cutting your baseplate.
Keep several copies of your confirmed template once the stoma has stabilised — they are useful if you ever need to cut an appliance away from home.
Step 5 — Transfer the Template to the Baseplate
Place the template on the inner (adhesive) side of the baseplate, draw around it, then cut just inside the traced line — most clinicians recommend leaving approximately 1–2 mm of clearance. Cut with small, smooth scissors strokes; avoid jagged edges, which can cause discomfort or trap output.
Step 6 — Check the Fit
Hold the cut baseplate over your stoma before applying it. The hole should encircle the stoma base without pressing into the mucosa and without leaving more than 1–3 mm of peristomal skin exposed. If either condition is not met, adjust the template before applying.
Special Situations
Flush or Retracted Stomas
A stoma that sits level with or below the skin surface (flush or retracted) can be more difficult to measure and seal effectively. In these cases, specialist convex appliances or additional accessories may be required. A stoma care nurse assessment is particularly important here — self-measurement alone may not be sufficient to select the correct product profile.
Mucocutaneous Separation or Irregular Edges
If the stoma has any areas where the mucosa has separated from the surrounding skin, or where skin folds encroach on the base, measuring from the outermost point of intact junction gives the safest aperture size. Do not cut the hole to accommodate a temporary separation; seek clinical advice.
The Bottom Line
Accurate stoma measurement is a straightforward but essential skill that protects your peristomal skin and ensures your appliance performs reliably. Measure at every change in the first weeks after surgery, revisit regularly once stable, and always create or update a personal template when your stoma shape changes. Individual anatomy varies considerably — always consult your stoma care nurse or clinician for personalised advice, particularly if you are struggling to achieve a secure fit or experiencing skin problems.
Free guide
The New Ostomy Patient Guide
Everything for the first weeks with a stoma — pouching, skin care, diet, and getting back to daily life. Written with stoma care nurses. Free, by email.
Common questions
Frequently asked questions
- How often should I re-measure my stoma?
- Most stomas change size noticeably during the first six to eight weeks after surgery as post-operative swelling resolves, so measuring before every appliance change during this period is good practice. Once the stoma has stabilised — typically confirmed at your routine clinic review — measuring every one to three months, or whenever you notice leakage or skin irritation, is usually sufficient. Significant weight gain or loss, pregnancy, or a parastomal hernia can all alter the stoma size and warrant a fresh measurement.
- What happens if I cut my baseplate hole too large?
- If the aperture is larger than the stoma, exposed peristomal skin is left unprotected and will be repeatedly contacted by output — whether faecal effluent or urine — causing moisture-associated skin damage, soreness, and potential breakdown. Over time this can make it harder to achieve a reliable seal. If you find your cut is too large, use a fresh baseplate rather than trying to patch it, and seek guidance from your stoma care nurse on how to achieve a more accurate template.
- Can I use a pre-cut appliance instead of measuring?
- Pre-cut appliances are convenient and reduce preparation time, but they are only appropriate once your stoma has been stable in size for several weeks and a custom template has been confirmed by your stoma care nurse. Using a pre-cut product whose aperture does not match your current stoma — particularly in the early post-operative weeks — carries the same risks as cutting too large or too small. Always verify the pre-cut size against a recent measurement before committing to a bulk supply.
- My stoma is not round — how do I measure an irregular shape?
- Many stomas are oval, kidney-shaped, or asymmetric rather than perfectly circular. In that case, measure the widest width from side to side and the longest height from top to bottom, then use these two dimensions to guide a hand-drawn template. Tracing directly around the stoma onto the template paper provided with most appliances is often the most accurate approach for irregular shapes. Your stoma care nurse can help you create and refine a personalised template.
- Does it matter whether I measure sitting or standing?
- Yes — body position can alter the stoma's apparent size and, more importantly, how it sits in relation to skin folds and the abdominal contour. Some people find their stoma appears to retract slightly when standing or sitting, which can affect the seal. Measuring and observing your stoma in the positions you spend most of your day in — sitting, standing, and bending — gives the most clinically useful picture and is something a stoma care nurse can guide you through during a practical session.
References