Buying baby clothes online means you can't hold the outfit up next to your baby before you click "buy." So how do you know if that adorable romper will actually fit, or end up in the too-small pile after one wear? A few minutes of checking the right details before you order can save you a return and a disappointed unboxing.
Start with the size chart, not the size label
The label says 12M, but that number means different things depending on the brand. Always check the seller's own size chart (usually measurements in inches or cm for chest, length, and sometimes weight) rather than assuming 12M means the same thing everywhere. Measure your baby, or use their current well-fitting outfit as a reference, and compare actual numbers instead of trusting the label alone.
Watch for brand-specific fit notes
Many product listings include a small note like "runs small, size up" or "true to size." Don't skip this line. It usually comes from real fit testing or accumulated customer feedback, and it can matter more than the chart itself. Cuts also vary by style: a fitted bodysuit and a loose romper labeled the same size can fit very differently on the same baby.
Read reviews with an eye for fit comments
Customer reviews are one of the best free tools you have. Skim for comments mentioning fit specifically, not just overall quality. A pattern of "ordered 6-9M but it fit more like 3-6M" across several reviews is a reliable signal, far more useful than a single five-star review that never mentions sizing at all.
Account for growth between ordering and arrival
Babies grow fast, and shipping takes time. If your baby is already near the top of a size range, or you're ordering for an event a few weeks out, sizing up slightly is often smarter than sizing exactly to today's measurements. This matters even more for wider age ranges like 1-4 years, where a two-year-old and a four-year-old can be very different sizes under the same label.
Know your baby's usual pattern
If you've noticed your baby consistently wears a size up or down from their age across multiple brands, that pattern usually holds for a new online purchase too. It's also worth checking whether baby clothes sizes tend to run big or small in general, since sizing conventions shift depending on the country and era of the brand.
When in doubt, check the return policy first
Even careful shoppers get it wrong sometimes. Before ordering, glance at the seller's return or exchange policy for sizing issues. Knowing you can easily size up if needed takes the pressure off getting it perfect on the first try.
Soft, breathable fabrics also make a borderline size more forgiving. If you're comparing materials while you shop, our guide to organic cotton baby clothes covers what to look for in fabric quality alongside fit.