FREE TOOL
Flange Size Calculator
The Flange Size Calculator finds your breast pump flange size in one minute. Measure your nipple diameter in millimeters and enter the number below. You receive a recommended flange size plus signs of a poor fit.
Measure, enter, and get your size
Enter your nipple diameter in millimeters for each side.
The calculator adds 3 millimeters for comfortable movement space.
This tool gives general sizing guidance only. Pain, injury, or ongoing supply concerns need a lactation consultant. Use the result as a starting point and adjust for comfort.
How to Measure Your Nipple Diameter
Measure after brief stimulation or pumping. Stimulation brings the nipple to its full size. Measure the base of the nipple only. Leave the areola out of the measurement.
Use a ruler or a printable nipple ruler in millimeters. Place the ruler across the base of the nipple. Read the diameter in millimeters. Measure both nipples separately.
Nipples change size during a pumping session. Measure again after a few minutes of pumping. Use the larger number when the two sides differ. Recheck your size after birth, supply shifts, or later size shifts.
How the Calculator Works
Enter your nipple diameter in millimeters. The calculator adds 3 millimeters for comfortable movement space. The result rounds up to the nearest standard flange size. Standard sizes run 15, 17, 19, 21, 24, 27, 30, 32, and 36 millimeters.
Enter each nipple separately when the sides differ. The calculator gives one size per side. Use the matching flange size on each side. Mixed sizes feel better than one compromise size.
Flange Size Chart
Signs Your Flange Fits
A good flange centers your nipple with room to move. Your nipple moves freely without rubbing the tunnel walls. Milk flows well and pumping feels comfortable. Your nipple keeps its shape after pumping.
A flange too small rubs your nipple against the tunnel. Rubbing causes pain, redness, or blisters. A flange too large pulls areola tissue into the tunnel. Low output and sore areolas signal a flange too large.
Pain during pumping never counts as normal. Stop and recheck your size when pumping hurts. Try one size up or down and compare comfort. Ask a lactation consultant for help when pain persists.
Tips for Comfortable Pumping
Lubricate the flange rim lightly before pumping. A small amount of coconut oil or nipple balm reduces friction. Center your nipple in the tunnel before you start. Sit upright and relax your shoulders.
Start on low suction and raise suction slowly. High suction from the start causes pain without extra milk. Keep sessions short at first with a new size. Comfort matters more than speed.
Frequently Asked Questions
What flange size do I need?
Measure your nipple diameter in millimeters and add 3 millimeters. Round up to the nearest standard size. A 17 millimeter nipple needs a 21 millimeter flange. Measure both sides separately.
What happens when the flange size is wrong?
A small flange rubs and causes pain or blisters. A large flange pulls areola tissue inside and lowers output. Both problems reduce milk flow. Correct sizing fixes most pumping pain.
Do I need different sizes for each breast?
Nipples often differ in size between sides. Measure each side separately. Use the matching flange size on each side. Mixed sizes feel better than one compromise size.
How often should I recheck my flange size?
Recheck after birth, supply shifts, or later size shifts. Nipple size changes across weeks of pumping. Recheck when comfort drops or output falls. A quick remeasure takes one minute.
Find Your Flange Size
Find your flange size now. Enter your nipple diameter above and try the recommended size. Comfortable pumping starts with the right fit.