UK Stoma Care · Flange Calculator + 1:1 Printable Card

Stoma Measuring Guide & Flange Aperture Calculator UK (mm + 1:1 Printable Template)

Work out your ideal baseplate/flange aperture (+2 mm snug clearance) for round or oval stomas, convert millimetres to inches, and print a bank-card-calibrated 1:1 UK measuring template.

Written by María G. · hola@siilostomy.com · Last updated: 14 November 20269 min read

Checking your stoma template weekly for the first 6 to 8 weeks after surgery prevents sore peristomal skin before ordering NHS pre-cut bags.

Quick answer

NHS stoma care nurses advise cutting your baseplate (flange) aperture 2 mm larger than the widest base diameter of your stoma (around 1 mm clearance all the way round)—snug enough to shield peristomal skin from output without rubbing the stoma mucosa. Enter your millimetre reading below or print the 1:1 template.

+2 mmideal total flange clearance (1 mm per side)
6–8 weekspost-op shrinkage window before pre-cut orders
Round & Ovalsupports symmetrical & oval stoma templates
1:1 A4 Printbank-card calibrated to exact 85.6 mm scale

Calculate your baseplate / flange cutting size (mm)

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UK Stoma Care · Flange Calculator + 1:1 Printable Card

Stoma shape at skin level

Horizontal base width (mm)

Vertical base height (mm)

Time since surgery

Recommended flange aperture (+2 mm)

27 mm

1-1/16 in (1.06")

Weeks 1–8 post-op: swelling reduces each week. Use cut-to-fit pouches and measure weekly before requesting pre-cut prescriptions.

Stoma base to flange cutting size chart (mm & inches)

Stoma base to flange cutting size chart (mm & inches)
Stoma Base (mm)	Imperial	Recommended Cut (+2 mm)	Imperial Cut	UK Prescription / DAC Note
18 mm	11/16 in	20 mm (20–21 mm)	3/4 – 13/16 in	Cut-to-fit / 20 mm
22 mm	7/8 in	24 mm (24–25 mm)	15/16 – 1 in	25 mm pre-cut (once settled)
25 mm	1 in	27 mm (27–28 mm)	1-1/16 – 1-1/8 in	28 mm pre-cut (once settled)
28 mm	1-1/8 in	30 mm (30–31 mm)	1-3/16 in	30–32 mm pre-cut
32 mm	1-1/4 in	34 mm (34–35 mm)	1-3/8 in	35 mm pre-cut (once settled)
35 mm	1-3/8 in	37 mm (37–38 mm)	1-1/2 in	38 mm pre-cut (once settled)
40 mm	1-9/16 in	42 mm (42–43 mm)	1-11/16 in	45 mm or cut-to-fit
45 mm	1-3/4 in	47 mm (47–48 mm)	1-7/8 in	48–50 mm or cut-to-fit
50 mm	2 in	52 mm (52–53 mm)	2-1/16 in	Cut-to-fit 52 mm

How to measure your stoma accurately at bag change

Measure right down at skin level
Remove your used bag with adhesive remover, clean gently with warm water and dry wipes, and measure from base edge to base edge.
Record width × height for oval stomas
Measure horizontal width and vertical height separately in millimetres, adding 2 mm to each axis on your cutting backing film.
Smooth the freshly cut rim with your finger
Run a clean finger round the inside of your cut baseplate hole to soften any tiny scissor ridges before applying.
Book a stoma nurse review if leaks start
Weight changes, parastomal bulges, or new tummy creases can alter fit—your NHS stoma nurse can adjust barrier rings or pre-cut sizes.

UK stoma measuring & flange cutting FAQs

How snug should my stoma bag hole fit?

Leave a 1 mm gap around the stoma edge (cutting the total hole 2 mm wider than your stoma base). That stops output touching bare skin while giving the stoma room to peristalse naturally.

When can I ask my GP or DAC to pre-cut my stoma bags?

Once post-operative swelling settles—usually around 6 to 8 weeks after surgery—most UK Dispensing Appliance Contractors (DACs) can laser-cut your pouches to your exact millimetre measurement free of charge.

What if my stoma is oval rather than round?

Measure both width and height in millimetres, trace an oval template onto the flange backing film, or ask your NHS stoma nurse about custom oval DAC cutting + a mouldable seal.

How do I check my printed A4 measuring card is true to scale?

Select '100%' or 'Actual size' in your printer settings and place any standard UK debit card over the 85.6 mm check bar before cutting out the circles.

More free SIIL interactive tools for UK ostomates

UK clinical reference sources: Aligned with peristomal skin care guidance from ASCN UK (Association of Stoma Care Nurses), NHS Stoma Care, and Colostomy UK. Educational guide; confirm template changes with your NHS stoma care nurse.

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