Breast Pump Flange Size Calculator
A correctly fitted breast pump flange makes pumping more comfortable and more efficient. Enter your nipple diameter in millimetres and get the recommended flange inner diameter, the nearest standard size, and the clearance gap — with guidance on what to look for if the fit still feels wrong.
mm
mm inner diameter — closest standard size at or above nipple + 3 mm clearance
- 1
Recommended flange ID
21 + 3 = 24Clinical guideline: flange inner diameter = nipple diameter + 3 mm clearance. - 2
Nearest standard size
24Round up to next available size (19, 21, 24, 25, 26, 28, 30, 32, 36 mm).
How does this calculator work?
Recommended flange inner diameter = nipple diameter + 3 mm, rounded up to the nearest standard size (19, 21, 24, 25, 26, 28, 30, 32 or 36 mm). Measure the nipple across its widest point after nursing or pumping. Pain or reduced output signal a poor fit — try the next size up or consult an IBCLC.
Formula
How this is calculated
The flange (also called a breast shield) is the funnel-shaped cup that fits over the nipple and areola during pumping. The inner diameter of the flange tunnel must be slightly larger than the nipple so it can move freely in and out without rubbing the walls — typically 2–4 mm of clearance, with 3 mm being the widely cited midpoint in IBCLC (International Board Certified Lactation Consultant) literature. A flange that is too small compresses the nipple base, restricts milk flow, and causes pain. A flange that is too large draws in areola tissue, reducing suction efficiency and causing soreness.
To measure: after a pumping or nursing session (when the nipple is at its largest), use a soft tape measure or nipple ruler placed across the widest point of the nipple shaft, excluding the areola. Record the diameter in millimetres. The calculator adds 3 mm and rounds up to the nearest commercially available size.
Standard sizes from major manufacturers (Medela, Spectra, Philips Avent, Elvie, Willow, Haakaa) range from 19 mm to 36 mm; the most common sizes are 24 mm (standard/medium) and 28 mm (large). If your calculated size sits between two standards, choose the larger option first and re-evaluate after a few pumping sessions. Nipple size can change throughout your lactation journey — re-measure if discomfort returns.
Frequently asked questions
Measure immediately after pumping or nursing, when your nipple is at its largest due to stimulation. Measuring a cold, unstimulated nipple may give a smaller reading that leads you to choose a flange that is too small once pumping begins. The measurement should be across the widest part of the nipple shaft, not including the areola.
A flange that is too small pinches the nipple base, restricts ductal drainage, causes blistering or bruising, and reduces milk output. A flange that is too large draws in areola tissue rather than nipple alone, which reduces the suction pressure on the ducts, may cause areola trauma, and also reduces yield. Pain during pumping is the clearest sign of a poor fit.
Yes — nipple size can increase in the early weeks of breastfeeding as tissue becomes more elastic, and may change again after supply is established. If you notice discomfort returning or your output dropping, re-measure and try a different size. Many mothers also find that their left and right nipples require different flange sizes.
TG we-Calculate Editorial Team. (2026). Breast Pump Flange Size Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/flange-size-calculator
TG we-Calculate Editorial Team. "Breast Pump Flange Size Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/flange-size-calculator.
TG we-Calculate Editorial Team, "Breast Pump Flange Size Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/flange-size-calculator
@misc{wecalculate_flange_size_calculator, title = {Breast Pump Flange Size Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/flange-size-calculator}}, year = {2026}, note = {TG we-Calculate} }
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