If you shop secondhand for kids, you already know the frustration: a size 6 from one brand fits like a size 8 from another, and the tag in a used shirt is often faded, cut out, or plain wrong. That is why we build every kids’ listing around measurements instead of a tag. Here is how to read a kids clothing size chart in resale, take three measurements at home, and stop guessing at checkout.
Why kids’ sizes are so inconsistent secondhand
Two things work against you. First, brands cut to their own standards — a children’s size 7 is a number the brand chose, not an industry rule. Second, used clothing has history. A cotton tee that has been washed forty times is shorter and narrower than it was new, and a stretch legging that has been worn hard sits looser than its tag suggests. Add hand-me-down relabeling and shrinkage and the tag becomes a starting hint, not an answer.
Measurements solve both problems at once, because they describe the garment in front of you today.
The three measurements that decide most fits
You do not need a tailor’s kit. A soft tape measure and two minutes gets you almost everything.
1. Chest (flat, pit to pit)
Lay the top flat and measure straight across from one armpit seam to the other. That number doubled is the garment’s chest circumference. Compare it to your child’s chest measurement and add room: about 2 inches of ease for a fitted tee, 3 to 4 for a sweatshirt or layering piece.
2. Length
For tops, measure from the highest point of the shoulder straight down to the hem. For bottoms, measure the inseam — crotch seam to hem — because that is what tells you whether pants will puddle or sit at the ankle. Waist-to-hem is nice to know but inseam is the decider.
3. Waist
Measure the waistband flat and double it. Then note whether it is elastic, has an adjustable interior button tab, or is a fixed woven waist. Elastic and adjustable waists buy you a whole growth season. Fixed denim waists do not.
How to build your own reference card
This is the trick that makes secondhand kids’ shopping fast. Take one garment per child that currently fits well — the shirt they reach for, the jeans they never complain about — and measure it. Write the numbers down in your phone notes:
- Best-fitting tee: chest flat, shoulder-to-hem length
- Best-fitting jeans: waist flat, inseam
- Best-fitting jacket: chest flat, sleeve from shoulder seam
- Shoe: insole length in inches, not just the size number
Now you have a personal size chart that works across every brand and every platform. When a listing shows measurements, you compare numbers to numbers. When it does not, you know exactly what to ask.
Reading measurements in a resale listing
Good listings tell you how the number was taken. “Chest 16 inches flat” means 32 inches around; “chest 32 inches” means the same garment. If a listing gives one number with no method, ask whether it is flat or circumference before you bid or buy. Also watch for these:
- Tagless or cut tags. Common in kids’ clothes and not a red flag by itself, but measurements become mandatory.
- Slim, husky, and plus kids’ cuts. Same number, different chest and waist. The cut word matters more than the size.
- Toddler versus little kids sizing. A 5T and a 5 are not the same garment; the T cut allows for a diaper-era rise and shorter length.
- Youth versus women’s smalls. A youth XL and a women’s XS overlap in chest but differ in length and shoulder width.
How much growing room to buy
Buying ahead is where resale pays off, and also where money gets wasted. Our rule of thumb: buy up one size for jackets, sweatshirts and elastic-waist bottoms, because a season of sleeve length is easy to live with. Buy true-to-measure for jeans with fixed waists, school uniforms and anything with a defined waist seam, because “they will grow into it” usually means it sits in a drawer for a year and then does not match the season it finally fits.
Shoes are their own category. Measure insole length rather than trusting the stamped size, and keep growing room to about a half inch. More than that and the shoe slides, which wears it out faster than the foot outgrows it.
Check condition against the measurements
Measurements tell you fit; condition tells you how long that fit lasts. A tee measured generously but thin at the shoulders has one season left. Check knees, cuffs, elastic recovery and seat seams on kids’ clothing specifically — those wear first. We walk through the whole process in our 7-point secondhand clothing condition check, and it pairs naturally with a tape measure.
A quick note on fabric
Cotton-heavy knits keep shrinking a little with hot washes, so if a top measures exactly at your target chest, expect it to land slightly under after a few cycles. Blends with elastane hold their numbers better but lose shape at the waistband over time. If you are sizing tight, size up a notch in cotton and stay true in blends.
Putting it together at checkout
The whole routine is short: know your child’s three numbers, know the numbers of a garment that already fits, compare against the listing, and confirm the cut and fabric. That is how families buy brand-name kids’ clothing secondhand without a pile of returns or a drawer full of almost-fits. It is the same discipline that makes budget wardrobe building work — we covered the broader version in our guide to saving on brand-name clothing.
When you are ready to shop, our current kids’ and family finds are on shop picks, and we call out measurements and condition live during our Whatnot shows, so bring your numbers and ask. We would rather measure a garment on camera than have it come back.