A flange that fits well is more comfortable and empties the breast better. Too small a flange rubs and pinches; too large pulls in the areola and can cause swelling. Nipple size can change during the first weeks of pumping, so re-measure if pumping becomes uncomfortable.
How to use the Breast Pump Flange Size Calculator
- Nipple diameter at the base
- Allowance
Results update as you type, and every field accepts the units shown in its menu.
How it works
Measure the diameter of your nipple at the base (not the areola) in millimetres, ideally after nursing or pumping. The calculator adds a 2–4 mm allowance and picks the nearest standard sizes.
Inputs explained
| Field | What to enter |
|---|---|
| Nipple diameter at the base | In mm |
| Allowance | Choose one: 2 mm (snug), 3 mm (typical), 4 mm (roomy) |
What each result means
- Ideal flange size = [Nipple diameter at the base] + [Allowance]
- Size range to try from = [Nipple diameter at the base] + 2
- Size range to try to = [Nipple diameter at the base] + 4
Example values
How the main result changes when Nipple diameter at the base changes and everything else stays at the example values above:
| Nipple diameter at the base (mm) | Ideal flange size (mm) |
|---|---|
| 8.5 | 12 |
| 12.75 | 16 |
| 17 | 20 |
| 21.25 | 24 |
| 25.5 | 29 |
| 34 | 37 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Ideal flange tunnel = nipple diameter (at the base) + 2 to 4 mm
Standard sizes: 13, 15, 17, 19, 21, 24, 27, 30 and 36 mm
Worked example
Inputs — Nipple diameter at the base: 17 mm; Allowance: 3 mm (typical).
Results — Ideal flange size = 20 mm; Nearest standard size (at or above) = 21 mm; Size range to try from = 19 mm; Size range to try to = 21 mm.
Key terms
- Flange
- The funnel-shaped part of a breast pump that fits over the breast.
Frequently asked questions
How do I know my flange is too small?
Rubbing, pinching, a nipple that does not move freely or white compression rings.
How do I know it is too big?
Much of the areola is pulled into the tunnel, or there is swelling or pain.
Do both sides need the same size?
Not always – measure each nipple separately.