How do you determine your nursing bra size?
Finding the right size nursing bra is essential for your comfort and for a smooth breastfeeding experience. However, with your breasts constantly changing, figuring out the right size can seem complicated.
At 23 Mai Paris, we support mothers every step of the way during their breastfeeding journey. This guide explains how to correctly measure your nursing bra size, when to do so, and how to choose the style that best suits your needs.
Why does bra size change while breastfeeding?
Your breasts undergo major changes during pregnancy and breastfeeding. Understanding these changes will help you choose the right size at the right time.
The stages of breast reconstruction
- Pregnancy (1st trimester): increased breast size and sensitivity → 1 to 2 cup sizes larger
- Pregnancy (3rd trimester): preparing for breastfeeding → back circumference may increase by one size
- Milk let-down (Days 2–5): engorgement, peak volume → temporary increase of 1 to 2 cup sizes
- Established breastfeeding (1–3 months): gradual stabilization → more stable size
- Extended breastfeeding (3+ months): milk supply may decrease → adjustment may be necessary
- Weaning: gradual reduction → return to previous size
Why a poorly fitting bra is a problem
- Too tight: compressed milk ducts, risk of mastitis
- Too big: no support, uncomfortable
- Improperly fitted braces: pain, pressure on the glands
- Hat too small: bulging, marks, discomfort
- Waistband too tight: difficulty breathing, red marks
Key takeaway: A well-fitting nursing bra supports your milk supply and ensures your comfort.
When should you measure your nursing bra size?
Timing is crucial for obtaining a reliable measurement.
The best times to test yourself
- 8th month of pregnancy: ✅ Perfect for your first purchase—your breasts are close to their breastfeeding size
- After the milk comes in (days 5–7): ✅ Adjust as needed; milk supply has stabilized after engorgement
- Around 6–8 weeks postpartum: ✅ For an additional purchase, breastfeeding is well established
- During engorgement: ❌ Avoid; breasts are temporarily swollen
- Immediately after a feeding: ❌ Avoid; milk supply is temporarily reduced
The best time of day
- Between feedings: ✅ optimal
- In the morning before the first feeding: ⚠️ often at maximum volume
- Immediately after a feeding: ❌ minimal volume
Tip: Measure your milk supply about 1.5 to 2 hours after a feeding, when your breasts are neither engorged nor completely empty.
How to Take Your Measurements Correctly
Grab a flexible measuring tape and follow these steps.
Step 1: Measure your back circumference (under the bust)
How to do it:
- Place the measuring tape just under your bust
- Measure around your chest, keeping it level
- The strap should be snug but not too tight
- Breathe out normally and note the measurement
Tip: The ribbon should slide easily without falling off.
Step 2: Measure your bust
How to do it:
- Place the measuring tape around the fullest part of your chest (at the level of your nipples)
- Turn around, keeping your back completely straight
- Don't pull it too tight; the ribbon should just graze the skin
- Write down the measure
Tip: Wear a thin, non-padded bra, or measure yourself without a bra for greater accuracy.
Step 3: Determine your size
The back measurement determines the size (number):
| Back circumference (cm) | French size |
|---|---|
| 63–67 | 80 |
| 68–72 | 85 |
| 73–77 | 90 |
| 78–82 | 95 |
| 83–87 | 100 |
| 88–92 | 105 |
| 93–97 | 110 |
The difference between the bust measurement and the back measurement determines the cup size:
| Difference (cm) | Beanie |
|---|---|
| 13 | A |
| 15 | B |
| 17 | C |
| 19 | D |
| 21 | E |
| 23 | F |
| 25 | G |
| 27 | H |
Sample calculation
Your measurements:
- Back circumference: 75 cm → Size 90
- Chest circumference: 94 cm
- Difference: 94 - 75 = 19 cm → D cup
Your size: 90D
The unique features of a nursing bra
Nursing bras have specific features that affect the choice of size.
What sets a nursing bra apart
- Opening clips: easy access to the breast — no impact on size
- Stretchable caps: adapt to changes — allow for greater flexibility
- No underwire: prevents compression — a different kind of support
- Wide elastic bands: comfort and support — more stable back support
- Adjustable straps: adapt to changes — extra flexibility
Types of nursing bras
- Nursing bra: for night, rest, and smaller busts — light support
- Wire-free bra: for everyday wear, all cup sizes — medium support
- Soft-cup bra: for larger busts, perfect for outings — strong support
- Nursing camisole: for night and home use — light support
- Nursing sports bra: physical activity — strong support
How to choose the right size for your situation
During pregnancy (8th month)
Choose your current size (your bust is close to its nursing size), buy only 1–2 bras (your size may still change), and opt for stretchy styles that will adapt to changes as your milk comes in.
After the outburst
Re-check your size if necessary (breast engorgement may have affected your measurements), invest in 2–3 high-quality pieces (you now know your consistent size), and keep a stretchy style on hand for days when you experience occasional engorgement.
For women with larger bust sizes (E and up)
For tops designed for larger busts, check out our nursing tops with flattering cuts.
Opt for wide straps (better support, less pressure), choose styles with soft underwires (superior support without compression), and check the cup depth—the cups should cover the entire bust.
For smaller bust sizes (A–B)
Signs of a poorly fitting bra
Too small
- If your breasts are spilling out of your bra cup, move up a cup size
- The back rides up: the back opening is too small
- The straps are digging in: the cup size or back size is too small
- Persistent red marks: overall size too small
- Pain or discomfort: change immediately
Too big
- The cap is gaping: move to the lower cap
- The back is higher than the front: the back is too long
- The straps keep slipping: the back band or cup size is too large
- No support: generally too large
The perfect fit
- Back circumference: horizontal, you can fit two fingers through
- Cups: cover the entire breast without spilling over
- Between the cups: pressed against the sternum
- Shoulder straps: snug without digging in
- Overall feel: comfortable fit—you’ll forget you’re even wearing a bra
How many nursing bras should I bring?
To calculate your total needs, check out our article How many nursing clothes do you really need?
The recommended amount
- Late pregnancy: 1–2 (size may still change)
- First few months: 3–4 (frequent washing due to milk leaks)
- Established breastfeeding: 3–4 (comfortable rotation)
The ideal distribution
- Comfortable day bra (2): for everyday wear at home
- More dressy bras (1): for going out, special occasions
- Night bra (1-2): night, rest
Our tips for a successful purchase
Key criteria
- Clips that are easy to use with one hand: you'll have your baby in the other arm
- Soft, breathable fabrics: sensitive skin, warmth
- Stretch tops: adapt to changes
- Wire-free (at first): prevents compression of the ear canals
- Easy to wash: frequent washing is required
Discover our Breastfeeding t-shirts soft and practical pieces to complete your wardrobe.
Recommended subjects
- Cotton: soft, breathable, hypoallergenic
- Bamboo: temperature-regulating, antibacterial
- Microfiber: stretchy, quick-drying
- Modal: ultra-soft, smooth
Mistakes to avoid
- Buying too many bras in advance: risk of getting the wrong size
- Choosing based solely on price: quality and comfort suffer
- Wearing an uncomfortable bra: a risk to lactation
- Skipping fittings: an unpleasant surprise when you use it
- Going back to your pre-pregnancy size: it will definitely be too small
Frequently Asked Questions
Can I wear my nursing bra at night?
Yes, if you'd like. We recommend wearing a soft, wireless bra at night. It keeps the nursing pads in place and provides light, comfortable support.
Check out our Breastfeeding pyjamas comfortable for sleeping
When should you switch to braces?
Once your breastfeeding routine is established after 6–8 weeks, you may want to consider bras with soft underwires if:
- Your milk supply is well established
- You don't experience frequent engorgement
- You need extra support (for a fuller bust)
Does my size change throughout the day?
Yes, that's normal! Your breasts feel fuller before feedings and softer afterward. That's why stretchy bras are recommended.
Do I need to buy nursing bras if I’m only breastfeeding for a short time?
Yes, even if you're breastfeeding for a short time. Your breasts will need proper support, and the openings make feeding much easier.
Conclusion
Measuring your nursing bra size correctly is essential for your comfort and to ensure a smooth breastfeeding experience. Take the time to measure yourself at the right time, choose high-quality, stretchy styles, and don’t hesitate to adjust your size as the weeks go by.
At 23 Mai Paris, we create nursing wear designed to support moms with comfort and style. To complement yourBreastfeeding dress practical tops, T-shirts, and dresses, discover our collection tailored to every stage of your motherhood journey.
Browse our collection of nursing clothes and build your growing wardrobe.
To prepare for breastfeeding, check out our article: Preparing for breastfeeding before the baby is born.
If you are breastfeeding, here are some of our nursing clothes that may interest you:
Breastfeeding t-shirts
Breastfeeding pyjamas
Breastfeeding sweatshirts
Zip-up nursing sweaters
Breastfeeding sweater dresses
If you are only a pregnant mom, here are our maternity clothes:
