Flange Size Calculator

A breast pump flange — also called a breast shield — is the funnel-shaped piece of plastic that fits over your nipple and areola during pumping. It creates the seal needed for suction. Choosing the right diameter is critical for comfort and milk output.

Use a ruler or a nipple ruler to measure the diameter of just your nipple — not the areola. Measure across the widest point of the nipple base. It's best to measure after a pumping session or when your nipple is in its natural state (not during pregnancy). Measure both breasts, as they can differ.

The standard recommendation is to add 3–4 mm to your nipple diameter to get your ideal flange size. For example, if your nipple is 16 mm wide, a 19–20 mm flange is typically recommended. This calculator adds 4 mm by default to give you a comfortable fit.

A flange that is too small will cause your nipple to rub against the tunnel walls, leading to pain, soreness, and reduced milk flow. A flange that is too large will pull excessive areola tissue into the tunnel, causing discomfort, swelling, and inefficient pumping. The right size allows your nipple to move freely with only a small amount of areola entering the tunnel.

If your nipple diameter is 23 mm, you would typically need a 26–27 mm flange. This calculator adds 4 mm to your nipple measurement, suggesting a 27 mm flange, which falls in the standard-to-large range available from most breast pump brands.

Yes. Nipple size can change throughout your breastfeeding journey due to engorgement, hormonal shifts, and the stretching effects of pumping over time. It's a good idea to re-measure every few weeks, especially in the early weeks postpartum.

Not necessarily. Many women have asymmetrical nipples and may need different flange sizes for each breast. This calculator accepts measurements for both nipples separately so you can get the right size for each side.

Most breast pump brands offer flanges ranging from about 17 mm to 36 mm. Common standard sizes include 21 mm, 24 mm, 27 mm, and 30 mm. If your calculated size falls between standard sizes, round up to the next available size for the most comfortable fit.