How to Choose the Right Maternity Bra Size

By Sustainable Underwear Australia | Published: 2026-10-17

Category: How-to Guides

Learn how to measure your maternity bra size at home with this step-by-step guide. Get tips on fit, comfort, and when to size up during pregnancy.

Quick Answer

To choose the right maternity bra size, measure your underbust and bust while standing, then use the difference to find your band and cup size. Because your body changes throughout pregnancy and postpartum, remeasure every 6-8 weeks and expect to go up at least one band and cup size from your pre-pregnancy bra.

Why Maternity Bra Sizing Matters

A well-fitting maternity bra supports breast tissue changes, prevents clogged ducts, and makes nursing easier. Many women wear the wrong size because they assume their pre-pregnancy band and cup will still work. But by the third trimester, your rib cage expands and your bust grows significantly. A bra that fits poorly can cause shoulder pain, chafing, and even affect milk flow. That is why using a proper maternity bra size guide and remeasuring regularly is essential.

When to Remeasure During Pregnancy

Your size changes most during the first trimester and again around month 7. Plan to measure at 8 weeks, 20 weeks, and 32 weeks. After birth, your size can shift again as milk comes in and your body adjusts. A bra that fits perfectly at 6 months may feel tight at 8 months. Instead of guessing, take 5 minutes to remeasure. This prevents the common mistake of buying bras that are too small in the cup or too loose in the band.

How to Measure Your Maternity Bra Size at Home

Step 1: Measure your underbust: Wrap a soft measuring tape snugly around your rib cage directly under your bust. Keep the tape parallel to the floor and breathe normally. Round the measurement to the nearest whole inch. If the number is even, add 4 inches to get your band size. If odd, add 5 inches. For example, a 30-inch underbust gives a 34 band. Common mistake: pulling the tape too tight. The band should be snug but not digging in.
Step 2: Measure your full bust: Stand straight and measure around the fullest part of your bust, usually at nipple level. Keep the tape loose enough to sit against your skin without compressing breast tissue. Round to the nearest whole inch. Checkpoint: do this in a non-padded bra or without a bra for accuracy.
Step 3: Calculate your cup size: Subtract your underbust measurement from your bust measurement. Each inch of difference equals one cup size: 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, and so on. Combine this with your band size from Step 1. For instance, a 34 band with a 3-inch difference gives you a 34C. Common mistake: ignoring that pregnancy swelling can make one cup larger. Always fit to the bigger side.
Step 4: Test the fit: Put on the bra and check the band: it should stay level across your back and not ride up. The center gore should lie flat against your sternum. Cups should fully enclose your breast tissue without spillage or gaping. Straps should stay in place without digging. Checkpoint: if the band rides up, go down a band size. If the gore floats, go up a cup size.
Step 5: Remeasure every 6-8 weeks: Your body changes faster than you expect. Set a recurring reminder to remeasure at each trimester milestone and again 2 weeks postpartum. Many women go up one band size and two cup sizes by the third trimester. Next step: once you have your current size, look for a maternity bra with adjustable features like drop cups and multiple hook rows to accommodate further changes.

Product Facts

Recycled Maternity Bra - Black: Don't worry about spending money on a short-term use item because our bra is 4 in 1 : Pregnancy - a non-wire bra comfortable enough to wear all day and sleep in; Feeding - a drop cup for easy one-handed feeding (because your other hand is busy!); Convert to a regular bra - see our video in the photo section to show you how; A sports bra, the clips mean you can convert to a racer back. A 4-in-1 design saves you from buying separate bras for pregnancy, nursing, and exercise. This is especially useful when your size changes multiple times, because one bra adapts without needing a new purchase each time.