# Breast Pump Flange Size Calculator

URL: https://speedycalculator.com/calculators/health/flange-size/
Last updated: 2026-10-30

> The flange size calculator recommends a breast pump flange (breast shield) size from your nipple diameter – the nipple measured at its base, plus about 2–4 mm – and suggests the nearest standard size.

## Inputs

- Nipple diameter at the base (mm)
- Allowance

## Results

- Ideal flange size
- Nearest standard size (at or above)
- Size range to try from
- Size range to try to

## 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
```

## Explanation

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

FieldWhat to enterNipple diameter at the baseIn mmAllowanceChoose 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)8.51212.7516172021.252425.5293437
*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.*

## 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.

## FAQ

**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.


## Sources

- [Academy of Breastfeeding Medicine – Clinical protocols](https://www.bfmed.org/protocols)