Maternity Size Converter

Find your maternity size from your usual pre-pregnancy size. Plus a trimester-by-trimester guide to what to buy and when.

Pre-preg → maternity US · UK · EU Trimester guide Free

Your maternity size

Recommended maternity size in each region
💡 General rule: Maternity sizing matches pre-pregnancy sizing in most brands. The clothes are cut wider in the belly + bust, but stay the same in shoulders, hips, and legs. Don't size up for the bump — that's already built in.

Trimester-by-trimester sizing guide

What to wear and what to buy at each stage. Most people don't need maternity clothes until the second trimester.

Weeks 1–13

First trimester

Bump usually not visible. Bloating, breast growth (1–2 cup sizes up) come first.

Buy now: nursing or stretchy "wireless" bras (1 size up), supportive non-wired sleep bras.

Skip: maternity clothes — you don't need them yet.

Bras first
Weeks 14–27

Second trimester

Bump shows. Regular pants stop closing. Bigger bust + slight back-pain risk.

Buy now: over-bump maternity jeans + leggings, side-ruched maternity tops, longer t-shirts, support bands.

Tip: over-bump beats under-bump as your bump grows.

Most maternity buys
Weeks 28–40+

Third trimester

Bump fully grown. Body temp runs hot. Swelling in feet/hands.

Buy now: dresses (last-trimester easy win), nursing-ready bras, slip-on shoes ½ size up.

Plan ahead: nursing tops, postpartum recovery underwear.

Add nursing prep

Popular maternity picks on Amazon

Best-selling, true-to-size maternity essentials.

Frequently asked questions

Do I size up for maternity clothes?

No. Maternity clothes are already cut wider in the belly and bust. Stay at your pre-pregnancy size. If you've gained substantial weight in non-bump areas (hips, thighs, shoulders), then consider sizing up one.

When do I start wearing maternity clothes?

Most people first reach for them in weeks 14–18 (early second trimester) when regular pants stop closing. Some need them earlier (second/third pregnancies, twins). Bras come first — most people go up 1-2 cup sizes by week 8.

What about plus-size maternity?

Plus-size maternity uses the same labeling (your usual size + "maternity"). Best brands: Motherhood, ASOS Curve Maternity, H&M Mama, PinkBlush Plus, Old Navy. Most run true to pre-pregnancy size.

Over-bump vs under-bump pants?

Under-bump: lower waistband sits below the bump. More comfortable early second trimester. Slides down easily as bump grows.
Over-bump: stretchy fabric panel goes over the entire bump. More supportive, stays in place. Best for third trimester. Choose over-bump for full pregnancy use.

What pre-pregnancy size do I shop after birth?

Plan to wear maternity clothes for 4–8 weeks postpartum. Your body needs time to recover. Most people fit back into pre-pregnancy clothes 3–6 months postpartum, but it's normal to be 1 size up permanently. Keep your maternity wardrobe — you'll wear it again.

Which brands run true to size?

True to size: ASOS Maternity, H&M Mama, Old Navy Maternity, Gap Maternity, Motherhood. Run small: Zara Mama (size up 1). Run large/loose: PinkBlush, Ingrid & Isabel (size down if between).