Sizing is where most kids swimwear complaints start. A "size 6" in the United States is not a "size 6" anywhere else — and in swimwear, where stretch, compression and coverage all matter at once, getting the grade wrong is far more expensive than in t-shirts. If you sell across borders, or manufacture with one factory for several markets, understanding how the three major sizing systems work is not optional.
Why kids sizing systems differ
Adult clothing has body-measurement standards that most markets roughly agree on. Children's clothing does not. Each region built its own logic:
- US system: sized by age (2T, 4T, 4, 5, 6, 7, 8, 10, 12…). The "T" stands for toddler and allows for a diaper; numbered sizes assume the average measurements of children that age. Because children of the same age vary enormously, US size charts usually list height and weight ranges alongside the age number.
- EU system: sized by height in centimeters (92, 98, 104, 110, 116, 122…). The number is literally the child's height in cm. It is the most measurement-honest system — and it means a European buyer will ask you for the finished-garment length, not the age the garment "should" fit.
- Latin America: mixed. Mexican and Colombian brands often use US-style age sizes, while Argentine and Chilean labels lean toward EU-style height numbers. Most Latin American buyers are comfortable with both, but they will test your chart against their own fit block, not against the theory.
Kids swimwear size conversion: US, EU and body measurements
The table below is a typical industry reference used by swimwear manufacturers for grading — the conversion most factories actually work from. Treat it as a starting point and always confirm the final spec with your factory before bulk production:
| US size | EU size (height, cm) | Height | Weight | Chest |
|---|---|---|---|---|
| 2T | 92 | 86–92 cm | 11–13 kg | 52 cm |
| 3T | 98 | 92–98 cm | 13–14.5 kg | 54 cm |
| 4T | 104 | 98–104 cm | 14.5–16.5 kg | 56 cm |
| 5 | 110 | 104–110 cm | 16.5–19 kg | 58 cm |
| 6 | 116 | 110–116 cm | 19–21.5 kg | 61 cm |
| 7 | 122 | 116–122 cm | 21.5–24.5 kg | 64 cm |
| 8 | 128 | 122–128 cm | 24.5–27.5 kg | 66 cm |
| 10 | 140 | 134–140 cm | 30–34 kg | 71 cm |
| 12 | 152 | 146–152 cm | 37–42 kg | 76 cm |
| 14 | 164 | 158–164 cm | 46–51 kg | 82 cm |
Note: chest measurements above are body measurements, not garment measurements. Swimwear fabrics stretch 20–40%, so the finished garment is cut smaller than the body it fits — your tech pack must state whether each number is a garment measurement or a body measurement, in relaxed or stretched state.
Swimwear fit is harder than fashion fit — here's why
A size chart that works for pajamas will not automatically work for a swimsuit. Three swimwear-specific factors decide whether a size range fits in real water:
- Stretch and recovery. Swim fabrics contain 18–25% spandex. The garment is intentionally cut smaller than the body, and the grade rule has to account for how much each size step stretches, not just how much it lengthens. This is where amateur grading fails first.
- Coverage across sizes. A one-piece for a 4-year-old and a 12-year-old are different garments in function: neckline depth, leg cut height and strap width all change with the age segment. Copying the base size's proportions up the range produces styles parents return.
- Water behavior. Swimwear gets heavier and longer in water. Factories compensate with tighter negative ease in the base pattern and with seam construction that resists drag. Ask how your factory's fit block handles this — the answer reveals their swimwear experience level.
What your factory needs from you (the spec checklist)
To grade your swimwear correctly, a factory needs more than "we want sizes 4–12". Send these five things and you cut the sampling rounds in half:
- Your size chart with body measurements for every size you will sell — in cm or inches, but pick one system and be consistent.
- Finished garment measurements for at least the base size, measured flat and relaxed, at every point of measure you care about (chest at 2.5 cm below armhole, front length, hip, etc.).
- Grading rules if you have them, or a fit reference garment the factory can measure and digitize.
- Tolerance standard — agree it in writing before sampling. (We work to AQL 2.5 across our girls swimwear and boys swimwear lines, which keeps size consistency measurable rather than debatable.)
- Your target market's labeling — EU buyers often want the height number printed on the care label; US buyers want the age size. Dual labeling on one garment saves a separate production run.
Common grading mistakes brands make
After years of manufacturing kids swimwear in Quanzhou, these are the errors we see most often in tech packs from new brands:
- Grading from a sample instead of a spec. If the factory grades your size-6 sample up to size 12 without a written chart, every size inherits the sample's fitting quirks. Specs first, grading second.
- Same ease for woven and knit. Some buyers send swimwear specs with t-shirt ease. Swimwear needs negative ease — the garment smaller than the body — or it bags in the water.
- No stretched-state measurements. A chest measurement taken relaxed tells the factory nothing about the fit. Specify the stretched state and the stretch percentage.
- Skipping the size-set sample. One sample in one size proves nothing about the range. Approve a full size set (every size you will sell) before bulk — sampling takes 7–10 days, and it is the cheapest insurance in the whole process.
How sizing works with our factory
Our factory in Quanzhou has manufactured kids swimwear since 2013, with 100+ workers and a monthly capacity of 80,000+ pieces across our girls swimwear, boys swimwear and baby swimwear lines. Here's how we handle sizing for brand clients:
- Your chart or ours: send your own size chart and tech pack, or start from our standard US/EU conversion chart and adjust from the size-set sample.
- Full size-set sampling: we cut and sew every size in your range for fitting approval — 7–10 days, graded from your approved base measurements.
- Written tolerances: AQL 2.5 quality control on bulk production, with measurement checks at agreed points of measure.
- Dual-market labeling: care labels can carry both the US age size and the EU height number, so one production run serves both markets.
MOQ is 100 pieces per style per color, bulk lead time 25–40 days, and we reply with a formal quotation within 24 hours on working days. Tell us your sizes, quantities and target markets — we'll confirm the grading approach in the quote, not after it.