Find Your Pump Flange Size
Measure your nipple diameter (base of the nipple, not including areola) after pumping or feeding. Add 2–4 mm to account for movement and swelling.
Measure in millimeters for best accuracy. If measuring in inches, the calculator converts automatically.
How to Use This Calculator
Measure after pumping or feeding
Use a ruler or caliper to measure the diameter of the nipple base when it is elongated but not swollen.
Add clearance for movement
Most lactation consultants recommend adding 2–4 mm to the measured diameter to prevent friction.
Test comfort and suction
Even with a recommended size, check for rubbing, blanching, or insufficient milk transfer. Adjust as needed.
Formula
Convert inches to millimeters: 1 inch = 25.4 mm
Optimal flange tunnel diameter ≈ Measured nipple diameter + 2.5 mm (adjust to 3–4 mm if swelling is expected)
Recommended flange size = Nearest commercially available size ≥ optimal tunnel diameter
Full Description
Proper flange fit enhances milk extraction efficiency and reduces nipple trauma. Too-large tunnels draw in areola, causing swelling, while too-narrow tunnels cause friction and blanching. This calculator aligns with lactation consultant guidance to add 2–4 mm to nipple diameter and select the next largest available flange size. Individual comfort and pump design still matter—trial and adjustment are encouraged.
Frequently Asked Questions
How often should I re-measure?
Reassess after engorgement subsides, postpartum body changes, or if pumping becomes uncomfortable.
Do silicone inserts change sizing?
Yes. Inserts reduce tunnel diameter. Follow manufacturer guidance or subtract insert thickness from the recommended size.
What if my measurement falls between available sizes?
Select the next size up and experiment with inserts or personal fit adjustments to fine-tune comfort.
Can I have different sizes for each breast?
Yes. Breast asymmetry is common. Fit each side independently to maximize comfort and milk flow.