Buying clothes across borders should feel exciting—not like a math quiz. Yet international sizing systems, different body measurement baselines, and fabric variations can turn a simple tee into a return headache. In this guide, I’ll break down how regional sizes actually work, what to measure (and how), and how to build a personal “size passport” to reduce returns—whether you shop for yourself or ship to friends and family abroad. I occasionally consolidate orders through Global Shopaholics, and the process taught me what really matters: objective measurements, fit intent, and a clear conversion plan, not just the letter on a tag.

Returns are costly for shoppers and retailers alike. Industry research estimated 16.9% of retail sales would be returned in 2024, underscoring how size and fit remain a stubborn challenge in apparel e-commerce.

Why international sizing is confusing (and how to think about it)

International apparel sizing isn’t a single language. It’s a patchwork of systems informed by local measurement units, standards, and population data. Understanding these differences helps you avoid guesswork.

1) Systems are built differently

• EU labeling (EN 13402) favors centimeter-based body measurements and pictograms, aiming to standardize labels around the body the garment is meant to fit—not a brand’s proprietary “small/medium/large.” The standard even recommends showing a body-dimension range (e.g., height 172–180 cm) to clarify fit. See [EN 13402 overview]. 

• US/UK/others often use alpha sizes (XS–XXL) and numeric systems for specific categories (e.g., women’s dresses, trousers), but baseline measurements and grading rules differ. A “10” in one region rarely equals a “10” in another.

• Asia (JP/KR/CN) commonly mixes numerical and alphabetical systems and may include height prominently. This is helpful when you know your exact stature (in centimeters).

Takeaway: Treat the label as a starting point. What matters is how your body measurements map to the system the region uses.

2) Standards vs. reality

Standards define what should be measured and how, but brands still interpret fit differently. ISO 8559-1:2017 outlines anthropometric definitions (the how of measuring people) used to build size and shape profiles—essential for any size chart that claims to be evidence-based. If a chart references ISO-type measurements (bust, waist, hip, etc.) you can trust it more than a vague “fits true to size.” See the [ISO 8559-1 description] and a plain-English [ANSI explainer (2023)].

3) People vary by region

Average body dimensions differ globally (height is an obvious example), which explains why a “regular” fit in one market feels long or short elsewhere. Our World in Data compiles historical and recent anthropometric trends showing meaningful regional variation. The lesson: don’t copy and paste your domestic size when you shop abroad—validate with measurements. Explore [height data & methods].

4) Fit, fabric, and manufacturing choices

Vanity sizing, design ease (the intended looseness), fabric stretch, and finish treatments (e.g., pre-shrinking) all shift how a garment feels on the body. That’s why two “mediums” can drape differently—sometimes dramatically.

The practical framework: Pick your fit, measure right, convert once

Below is a step-by-step method I use before ordering from a new region or label. It blends standards-based measuring with real-world guardrails.

Step 1 — Decide your fit intent (before numbers)

Are you after slim, regular, or relaxed/oversized? Write that down first. It sets your tolerance for size up/downs and helps you interpret charts (e.g., you may size up 1 step for relaxed fits in woven fabrics with no stretch).

Step 2 — Take four core body measurements (ISO-aligned)

Use a soft tape, stand naturally, and measure over light clothing:

• Chest/bust (fullest point)

• Waist (natural narrowest point)

• Hip (fullest seat)

• Height (and inseam for bottoms)

Record in centimeters and inches. ISO 8559-1 defines these terms consistently, so you’re speaking the same language as better size charts. See [ISO 8559-1 outline] for what each measure means. ISO

Step 3 — Translate to the region’s system

• For EU charts that follow EN 13402, map your measurements to the range printed on the label (e.g., chest 94–102 cm = “M” for men; women’s dress charts show step-wise bust/waist/hip ranges). See [EN 13402 summary & tables].

• For US/UK/Asia, use the brand’s conversion chart and treat it as a hypothesis to test against your body and garment measurements (next step).

Step 4 — Prioritize garment measurements when available

If the product page lists the actual garment dimensions, compare them to a similar item you own (the one whose fit you love). Lay it flat and measure across chest, shoulders, waist, rise, thigh, inseam, and back length (as relevant).

• If your favorite shirt measures 54 cm pit-to-pit (≈108 cm chest circumference) and the item’s “M” is listed at 56 cm, you can expect a slightly looser fit unless fabric or patterning changes it.

Step 5 — Adjust for fabric behavior

• Knits/jersey with elastane can tolerate closer sizing (they stretch).

• Wovens (denim, poplin) need more ease.

• Unwashed denim or cotton can shrink; pre-shrunk or mercerized fabrics move less.

• Bias-cut garments drape differently and may “give” over time.

Step 6 — Add policy and logistics to your calculus

Check return windows, fees, and cross-border logistics. Even if you size carefully, you’ll want an exit if something feels off. Returns surged in recent years, and apparel plays a large role; many retailers have tightened policies to curb costs. The [NRF 2024 returns report] captures the macro trend. 

Step 7 — Build your Size Passport

Keep a note on your phone with:

• Your body measurements (cm + in) and fit intent

• Garment measurements of staples (favorite tee, trousers, jacket)

• Conversion notes by region (e.g., “EU medium = great in shirts if chest 108 cm garment; UK trousers: prefer 1 size up if inseam < 32 in”)

This becomes your personal truth when charts disagree.

Regional quick notes (without the myths)

Use these as heuristics, not hard rules.

European Union (EN 13402)

• Labels often center on body measurements in centimeters (e.g., chest, waist, hip), sometimes with height as a key selector for categories like trousers.

• When labels show a range (e.g., height 172–180 cm), it reflects the design target and ease built into the garment—not a guarantee of tightness or looseness. See [EN 13402 guidance]. 

United Kingdom & United States

• Expect alphas (XS–XXL) plus numeric categories (e.g., women’s dress sizes, men’s waist/inseam).

• Numeric systems may not align between the two markets; designers use different grading increments. Use your measurements, then compare to garment specs when available.

East Asia (Japan, Korea, China)

• Numeric and alpha systems coexist; you’ll often see height emphasized.

• Slimmer baseline cuts are common in some segments; validate with garment measurements and fabric stretch.

How “size & fit” drives many returns (and what to do about it)

Across studies, size and fit issues consistently top the reasons for returns. In a U.S. consumer report, 45% of returns in 2022 were attributed to size/fit—up from 38% in 2020—showing the problem has been getting worse as online apparel booms. See [Narvar’s State of Returns]. Narvar

What this means for cross-border orders:

• Measure once, buy many times. Once your Size Passport is set, repeat orders become easy—even across regions.

• Don’t chase the number. A “large” that perfectly fits is just your size; the letter is arbitrary across systems.

• Use material cues. The same chart can fit differently in a heavy cotton twill vs. a lightweight rayon blend.

• Expect edge cases. Tailored garments, formalwear, and structured outerwear behave differently from tees and joggers.

Measurement quick-reference (save this)

Upper-body essentials

• Chest/bust (body): fullest part, tape parallel to floor

• Shoulder (garment): seam-to-seam across back

• Sleeve (garment): shoulder seam to cuff, and center-back to cuff

• Length (garment): highest shoulder point to hem

Lower-body essentials

• Waist (body): natural narrowest point

• Hip (body): fullest seat

• Rise (garment): crotch seam to waist (front/back)

• Thigh (garment): 1–2 inches below crotch, across leg

• Inseam (garment): crotch seam to hem

Pro tip: For tops, comparing garment chest and shoulder width to a favorite piece predicts fit more reliably than size letters.

Trade-offs & decision rules that actually work

When between sizes, consider:

• Fabric & ease: No-stretch wovens = err up for comfort; high-stretch knits = you can go truer (or down for snug).

• Use-case: Layering or all-season wear argues for slightly larger; tailored silhouettes argue for precision (and possibly local alterations).

• Return friction: If cross-border return fees are steep, lean toward the safer size based on garment measurements—and re-sell locally if needed.

Pros & cons of “buy two sizes”

• Pros: Reduces uncertainty when return shipping is cheap/easy.

• Cons: Environmentally and financially inefficient; some merchants now discourage excessive returns and may charge fees or shorten windows as return volumes grow. See [NRF 2024 returns analysis] for context.

Region-aware checklist before you check out

• Lock in your Fit Intent (slim/regular/relaxed).

• Confirm four core body measures (cm + in).

• Map to the region’s logic (EU ranges vs. US/UK letters; Asia height cues).

• Prefer garment measurements over label letters.

• Read fabric composition (and note stretch/shrink behavior).

• Scan return policy & fees, especially cross-border.

• Save what worked into your Size Passport for effortless reorders.

Why these standards and datasets matter

When a product page references ISO 8559-1 definitions or follows EN 13402 ranges, it’s signaling that its sizing logic is grounded in anthropometry—not guesswork. Pair that with population-level insights (like global height distributions) and you gain a durable framework to buy confidently across borders, season after season. For more, see [ISO 8559-1], [EN 13402], and [Our World in Data’s height work].

Conclusion: A neutral recap

Sizing abroad becomes straightforward when you stop chasing the letter on a tag and start with your measurements, your fit intent, and the region’s labeling logic. Standards like ISO 8559-1 (how to measure) and EN 13402 (how to label) help you read charts accurately; population differences explain why “regular” in one country can feel long or short in another; and paying attention to fabric and garment measurements closes the loop. Returns remain a real cost for the industry—size/fit is still a leading cause—so a personal Size Passport is your best insurance policy. That’s been my experience as a frequent cross-border shopper—and it’s why I plan my orders carefully when I ship with Global Shopaholics.