Activewear Size Guide for Brands: S/M/L vs US 4/6/8/10, Leggings and Sports Bra Sizing, and Custom Grading

Quick Answer

In most activewear size guides, S = US 4–6, M = US 8–10 and L = US 12–14. This is a retail convention, not a standard. If you are launching your own activewear label, the bigger question is where you sell. Leggings, sports bras and yoga sets are designed to fit smaller than the body and rely on stretch. A size M developed on Asian sizing will therefore often run small for US customers and short for Dutch customers. This guide shows how to confirm your market, decide how much to size up, and choose between in-stock styles, graded sizes and custom sizing.

Why Activewear Cannot Simply Borrow Regular Clothing Sizes

Size standards describe bodies. Activewear is made to be smaller than the body and to stretch. That gap is why a standard size chart is only a starting point for leggings, sports bras and yoga sets.

A dress or a shirt is usually cut larger than the body, with room to move. A pair of gym leggings or a sports bra is the opposite. It has negative ease: the garment is smaller than the body and holds its shape through fabric stretch and recovery. It also has to survive squats, lunges, running and washing.

This changes how sizing works:

• The same body can wear different sizes in different activewear, depending on compression level.
• A size label says little unless it is paired with fabric stretch and garment measurements.
• Sizing has to be checked in motion, not only on a still body.

The next sections cover the standards first, then how they apply to activewear.

S/M/L vs US 4/6/8/10 in Activewear

Letter sizes (S, M, L) are brand labels. US numeric sizes (4, 6, 8, 10) are tied to a body-measurement standard, ASTM D5585. In activewear they are often printed side by side, for example “S (US 4–6)”, but the link between them is a habit of the trade.

ASTM D5585 gives body measurements for each numeric size. It does not define S, M or L.

Source: ASTM D5585, Misses body measurements. These are body measurements, not garment measurements. Verify against the current edition before use.

Brands differ. Some treat S as US 4 only, some put US 10 in L, and some use combined sizes such as S/M for leggings or sports bras. Customers also report wearing one size in leggings and another in a sports bra or jacket. For your own brand, always publish measurements next to the letter.

How Activewear Sizes Are Labeled in Different Markets

Your labels should follow what customers in your target market expect.

• United States: Letter and numeric sizes are often shown together, such as “S (US 4–6)” on leggings and sports bras.
• European Union: EU numeric sizes are common, often alongside letters.
• United Kingdom and Australia: Numeric sizes are common alongside letters. They differ from US numbers, so check your sales channel’s requirements before printing labels.
• China and much of Asia: Letter sizes are most common. Chinese garments also use height/bust/body-type designations such as 160/84A.

For leggings, the label is usually tied to waist and hip. For sports bras it is tied to bust and underbust, and sometimes to cup. Because of this, a single label on a matching yoga set may not mean the same thing on the top and the bottom.

GB/T 1335.2, ASTM D5585 and EN 13402 Compared

The three systems describe bodies in different ways, so they cannot be converted with one formula. China uses height/bust/body-type designations, the US uses point measurements per numeric size, and the EU uses body-measurement intervals. None of them was written specifically for stretch activewear.

China (GB/T 1335.2-2008). Sizes are written as height/bust/body type, for example 160/84A. “A” means a standard body type with a bust-to-waist difference of 14–18 cm.

GB/T defines designations, not letters. S = 155/80A is a trade convention.

Europe (EN 13402). The standard defines how to measure and label body dimensions, using intervals. It does not say that S equals EU 36 or 38. The women’s example table in EN 13402-3 uses 4 cm steps:

Source: EN 13402-3 example data. These are body-dimension steps, not an S/M/L chart. Verify against the standard before use.

Reference mapping for activewear buyers

Reference mapping only. This table is for buyer–supplier communication. It does not mean a Chinese M is always a US S or an EU 36. Each brand chooses its own fit, ease and size combinations.

A simple note for your activewear product pages:

Size system note: Chinese sizing follows GB/T 1335.2 designations such as 160/84A; US sizing follows ASTM D5585 point measurements; EU sizing follows EN 13402 body-measurement intervals. Letter sizes are commercial conventions and are not directly interchangeable across systems. Activewear garment measurements are shown before stretch.

Why the Same M Fits Differently in Different Markets

Three things change: the body data, the fit preference and the fabric stretch.

Body data. US CDC/NCHS data (NHANES, August 2021–August 2023) show that US women aged 20 and over have an average measured height of 63.5 in (161.3 cm) and an average waist circumference of 38.5 in (97.8 cm). It is an all-adult average, but it shows why a Chinese M legging designed around a waist of 67–70 cm can be small for a meaningful share of US customers.

The Netherlands. CBS StatLine (table 81565NED, updated through 2024) reports height by sex and age group. Height there is self-reported. For Dutch women aged [age group], the figure is [CBS value, to be filled from the table]. The Dutch difference in activewear is mostly about length, not circumference. Section 7 covers this. For circumference and percentile data for grading, the DINED database (TU Delft / TNO) is the better source.

Fit preference by use. Activewear is bought for different jobs, and the preferred fit changes with the job:

Use	Typical fit preference	What it means for sizing
Yoga and studio	Soft, close, not restrictive	Waistband comfort and no-pinch fit matter; customers may choose the size that feels softer
High-intensity training	Compression and support	Higher compression can lead customers to size up; leggings must stay put in squats and lunges
Running	Secure, low-friction, no rolling	Waistband hold, seam position and length matter
Everyday athleisure	Regular to relaxed	Customers often choose a larger size for comfort

General industry observation, not a standard. Your own customers should guide the final decision.

So the same customer may buy different sizes for a compression gym legging and a relaxed athleisure set. This is one reason brand owners should avoid assuming one size range for every product.

How Many Sizes Up for Each Market? Our Experience

In our experience, products developed on Asian sizing often need to go up 1–2 sizes to suit European and US customers. This section reflects what we have seen working with activewear brand customers.

• Asian-sized activewear often needs 1–2 sizes added for the European and US markets.
• Products already in US or EU sizing may still need another 1–2 sizes for US and Dutch customers. In the US this is mostly about circumference. In the Netherlands it is mostly about length.
• These two markets are where we see sizing questions come up most often. The final decision depends on how you read your own market, so how much to grade up is up to you.
• If standard sizes still do not fit your customers, the next step is your own custom size chart. This is a custom product and needs a minimum order quantity.

Compression and relaxed styles behave differently here. A high-compression legging leaves little room for a customer who is between sizes, while a relaxed training tee is more forgiving. That is experience, not a rule, and your own customers matter more than any rule of thumb.

Length: The Activewear Problem Most Size Charts Miss

Length is not solved by adding circumference. In the leggings measurements in our own catalog, each size up typically adds about 4 cm to waist and hip, but only 1–2 cm to overall length. A taller customer can fit at the waist and hip and still find the legging short.

In activewear, length problems show up as:

• Leggings: Short legs that ride up, or a waistband that rolls or slips. The gap between a 7/8 length and a full-length legging also changes by customer height.
• Rise: A short rise can cause the waistband to roll or sit low when the customer bends or squats.
• Training tops and tees: Body length affects whether the hem rides up during overhead movement.
• Sports bras and crop tops: Band and strap length affect support and comfort.
• Hoodies and jackets: Sleeve length and shoulder position.

This is why Dutch customers may find that a legging fits at the waist and hip but feels short. Before you size up, check whether the problem is circumference, length or both. If it is length, a larger size alone may not fix it, and a length adjustment in your own size chart may be needed.

Note: our catalog lists leggings overall length, not inseam. State clearly in your own chart which one you use.

Garment vs Body Measurements, and What Stretch Changes

Body measurements describe the person. Garment measurements describe the product laid flat, before stretch. Mixing them up is one of the most common causes of activewear returns.

Leggings and sports bras are usually smaller than the body they are made for. The stretch a garment needs can be estimated:

Required stretch = target body measurement ÷ static garment measurement − 1

An anonymized example: take a US 8 body (waist 68.6 cm, hip 95.3 cm) and two M-labeled leggings.

Both are labeled M, but Legging 2 asks much more of the fabric and will feel much tighter. The label alone tells a buyer very little.

What stretch does to the fit range. Stretch mainly extends a size toward smaller bodies. It does not raise the upper limit much. As a rule of thumb, regular stretch can extend the waist range 3–5 cm lower, and the hip and bust 2–4 cm lower. High-compression styles should be more conservative.

Illustrative example: a Chinese M legging designed for a waist of 67–70 cm, hip of 88–92 cm and thigh of 52–56 cm, in a 4-way stretch fabric with 60% crosswise stretch.

Stretch solves “too big”. It does not solve “too small”. That is why markets with larger average circumferences often need grading up, not just stretch.

Activewear also has two issues general clothing does not. Waistband recovery matters, because a waistband that stretches out after a few wears feels like the wrong size. Wash shrinkage and shape change matter too, because they shift the real size range after purchase.

Activewear Size Guide by Product Category

Each activewear category needs its own size logic. Do not use one chart for everything.

Leggings and yoga pants. Check waist, hip, thigh and overall length. Confirm compression level, fabric stretch and waistband recovery. Test squat, lunge and bend for transparency and rolling.

Sports bras. Bust and underbust matter more than waist. Support level (low, medium, high) changes the right size, and high-support styles often fit more firmly. Check band recovery and strap length.

Yoga sets. Tops and bottoms may need different sizes. Offer clear measurements for each piece, and consider whether customers can mix sizes.

Training tees and tanks. Check bust, shoulder, body length and armhole. Look at how the hem behaves in overhead movement.

Shorts. Waist, hip, rise and leg opening. Check that shorts stay in place during running or lifting.

Men’s training wear. Do not use a women’s chart. Chest, waist and length steps are different and need their own table.

Team wear. Teams include many body types. Plan a wide size range, check length as well as circumference, and consider a fitting round before the full order.

Gyms and yoga studios with a house brand. Members span a much wider range of body types than a typical retail customer. Plan a wider size range than you might for a small retail drop, and consider letting members try samples before you commit to a larger order.

Children’s activewear follows different standards and should not be derived from adult charts.

Seamless Knitting vs Cut & Sew in Activewear

In seamless activewear, size is set largely by the machine. In cut & sew, it is set by the pattern.

Seamless. Our seamless garments are knitted on Italian Santoni machines (SM8-TOP2V and TOP2 FAST) at a standard 28 gauge. The garment is knitted in one piece, so there are no side seams, which reduces friction against the skin. Different zones can carry different stretch or support, which suits yoga sets, sports bras and leggings. Size depends on cylinder diameter and needle count. For example, a 13-inch barrel has 1,152 needles, and each additional inch of diameter adds 96 needles. Size steps are therefore tied to the machine setup.

Cut & sew. Patterns are cut and graded for each size, then sewn using four-needle six-thread flatlock and three-needle five-thread coverstitch on Juki and Pegasus machines. This gives more freedom to control individual measurements, such as length, in each size. Flatlock and coverstitch seams are common on gym leggings and training tops, where seams need to lie flat and handle stretch.

Both are made in our own factory. Custom cut & sew starts at 100–200 pieces per color, and custom seamless at 450–500 pieces per style.

Standard Size, Graded Size or Custom: How to Decide

Start with what already exists, and move to custom only if it does not fit.

1. Pick your target market and use. US, Netherlands and other markets can differ in circumference and length. Yoga, training, running and athleisure also fit differently.
2. Compare body data and fit preference with the measurements of a sample garment.
3. Try in-stock activewear first. In-stock orders start from 1 piece, and stock samples take 2–3 days. It is a low-risk way for a new brand to test fit with real customers. Our catalog lists garment measurements for each style, and sizes vary between styles because of pattern and fabric. See the catalog: [Get catalog page link].
4. If you are not sure about sizing, order a sample. If you are a first-time customer and the numbers are not enough, we can send a sample for you to try.
5. Grade up if needed. If standard sizes run small for your market, adding 1–2 sizes or grading for your market is the usual next step.
6. Go custom if nothing fits. A custom size chart is a custom product and needs a minimum order quantity. Sampling takes 8–15 days. Bulk production takes 25–35 days for cut & sew and 40–45 days for seamless.

How to Build Your First Activewear Size Chart

A useful activewear size chart has measurements, not just letters.

Four steps

1. Choose the measurements for each category (leggings: waist, hip, thigh, overall length; sports bras: bust, underbust; tops: bust, shoulder, body length, sleeve length).
2. Separate body size from garment size. Show both if you can, and label them clearly.
3. Set the fit range for each size, using the fabric’s real stretch and your target compression level.
4. Show letter and numeric sizes together where your market expects it.

Six tests before you publish

1. Static fit: Stand and check waistband, hip, thigh and crotch.
2. Dynamic fit: Squat, lunge, lift the leg, bend and jump, and look for transparency, rolling, slipping and marks.
3. Recovery: Wear and remove several times, then re-measure.
4. Extreme sizes: Test the smallest and largest body in each size range, not only the middle.
5. After washing: Re-check stretch, waistband recovery and length.
6. Seam strength: More stretch puts more load on side seams, crotch and waistband.

Do not grade by one flat percentage. Waist, hip, length and straps each need their own step, and both ends of the range should be re-tested.

Buyer Checklist and Five Common Mistakes

Checklist before you place an activewear order

• Target market and use (yoga, training, running, athleisure) are defined.
• Size chart shows garment measurements, and body measurements if possible.
• Letter and numeric sizes are both shown where needed.
• Length has been checked separately from circumference.
• Compression level and fabric stretch are confirmed.
• A sample has been tried in movement, not only measured.
• Quality standard is agreed. Our process uses 5-stage 100% inspection at AQL 2.5.

Five common mistakes

1. Relying on the letter size alone.
2. Treating garment measurements as body measurements.
3. Using one chart for every market and every use.
4. Solving a length problem by adding circumference.
5. Skipping a sample or a movement test on real bodies.

FAQ

Need Help Choosing Activewear Sizes?

CFC Activewear is a custom activewear manufacturer with its own factory: 12,000 m², 180+ employees and an annual capacity of 2.5 million pieces. Our textile roots go back to 1999, and the factory was formally established in 2014. We keep 100,000+ finished pieces and greige fabric in stock. Our certifications include Amfori BSCI, GRS and OEKO-TEX® Standard 100.

• Browse our in-stock activewear: [Get catalog page link]
• Send us your target market and styles, and we will help check sizing and arrange a sample: [Contact page link]