How to find your flange size

Almost every pump ships with a 24 mm flange because it fits the largest single share of people. That is not the same as fitting most people. Sizes in regular use run from about 13 mm to 30 mm, and someone who needs 19 mm will spend weeks blaming the pump, the level, or themselves before anyone mentions the tunnel is too wide.

What you are measuring

The flange size refers to the nipple diameter, not the areola and not the breast. Measure across the base of the nipple at its widest point, in millimeters, and ignore the areola entirely. A ruler with millimeter markings works. So does the measurement card in the box of every Lulia wearable.

Measure when you are not swollen and not immediately after a session, because both change the number. Then add 1 to 2 mm for movement inside the tunnel. If you measure 17 mm, start at 19 mm.

What the wrong size feels like

What you notice	Usually means
Areola pulled deep into the tunnel	Flange too large
Nipple rubs the sides, goes white or sore	Flange too small
Milk flows, then stops early	Often size, sometimes valve wear
Pinching at the base with every pull	Too small, or level too high

A correct fit moves the nipple freely in the center of the tunnel with only a little areola drawn in, and it should not hurt. Pain is information. It is not something to push through to get a better session.

Both sides can differ

Bodies are not symmetrical, and it is common to need one size on the left and another on the right. Our wearable kits include 17, 19, 21 and 24 mm inserts partly for that reason: mixing sizes across two cups costs nothing when all four are in the box.

When to measure again

Size changes over the first weeks and again as feeding settles. If pumping was comfortable in month one and started hurting in month three without anything else changing, measure again before adjusting anything else. Swelling in the early days can also make an accurate measurement impossible, so treat the first reading as provisional.

Before you change the suction level

The order that saves the most time: check the flange size, check the valve for wear, check the seal, and only then think about levels and modes. Turning the suction up to compensate for a bad fit makes the fit problem worse.