The most common question we get about the ASICS tracksuit range is also the simplest to answer. It fits true to size. If you wear a medium in most brands, order a medium. There is no hidden trick, no vanity sizing, no need to go up two sizes because somebody on a forum said so.
That said, "true to size" covers a lot of ground. The jacket and the pant in the Black Core Tracksuit at £149.99 do not fit the same way as each other, and people who layer have a decision to make that people who do not layer can ignore entirely. This guide goes through both pieces properly so you order once and keep it.
Everything below applies to the ASICS Core range specifically. The Road range runs slightly differently, and the trainers are a separate conversation, which we cover further down.
The short version
Order your normal size in both the jacket and the pant. The only reason to deviate is if you plan to wear a hoodie underneath the windrunner, in which case size up one on the jacket and leave the pant alone.
That is genuinely it. Everything that follows is detail for people who want to understand why.
How the Core Windrunner jacket fits
The Core Windrunner is £89.99 bought on its own. It is cut as a running shell, which means it is not tight but it is not oversized either. The shoulders sit where your shoulders are. The body has enough room for a t-shirt and a bit of movement, and the hem sits around the top of the hip.
It is 100% polyester and water-repellent, so there is no stretch in it. This matters more than people expect. A cotton jacket that is slightly snug will give after a few wears. A polyester shell will not. If the chest feels tight when you zip it up over a t-shirt, it will feel tight in six months.
When to size up
Size up one if any of these apply:
- You want to wear a hoodie or midlayer under it in winter
- You are between sizes and would rather have room than not
- You prefer a looser, more relaxed look through the body
Do not size up if you are wearing it over a t-shirt or a vest. You will get a jacket that looks borrowed.
Sleeve length
Sleeves run slightly long, which is normal for a windrunner. They are meant to sit at the base of the thumb when your arms are down. If you have shorter arms than average, the cuff will bunch a little. That is cosmetic rather than a fit problem.
How the Core Woven Pant fits
The Core Woven Pant is £54.99 separately. It has an elasticated waist with a drawcord, so the waist is forgiving in a way the jacket is not. If you are between sizes on the waist, take the smaller one and pull the cord.
The leg is a straight taper. Not skinny, not wide. It sits on the trainer rather than pooling over it, which is why they work with chunkier silhouettes like the Gel-Kayano 14 without looking off.
Do not size up on the pant to match a sized-up jacket. The elasticated waist means a size up will sit low and the leg will be too long. Mismatched sizes across the two pieces is completely normal and nobody can tell.
Size-by-size reference
| If you normally wear | Jacket (no layer) | Jacket (hoodie under) | Woven pant |
|---|---|---|---|
| Small | Small | Medium | Small |
| Medium | Medium | Large | Medium |
| Large | Large | XL | Large |
| XL | XL | XXL | XL |
| Between two sizes | Smaller | Larger | Smaller |
Full measurements are on our sizing guide page if you want to check against a garment you already own. That is more reliable than guessing from a brand comparison.
Sets and tri-sets fit the same way
The sizing does not change when you buy the pieces together. The Black Core Tracksuit Tri-Set at £174.99 adds a tee to the same jacket and pant, and the Black Core Windrunner Set at £129.99 pairs the jacket with shorts instead.
Shorts come in 5in and 7in lengths. That is a style choice rather than a sizing one, and we have gone through it properly in our 5in vs 7in shorts guide.
Tees in the sets, including the Black Core T-Shirt Set at £74.99, are a regular fit. Normal size again.
Trainer sizing is different
Do not assume your clothing size logic carries over to the Gel models. It does not, and the three models do not even agree with each other.
| Model | Sizing | Notes |
|---|---|---|
| Gel-Kayano 14 | True to size | Roomiest of the three |
| GEL-1130 | Half a size up | Runs snug |
| GEL-NYC | Half a size up | Runs snug |
If you are buying trainers alongside a tracksuit, each model has its own sizing article: Gel-Kayano 14 sizing, GEL-1130 sizing and GEL-NYC sizing.
If you get it wrong
Order the size you think is right and send it back if it is not. Our returns policy covers unworn items, and orders over £100 get free UK delivery, with same day dispatch on orders placed before 2PM. Klarna and Clearpay are both at checkout if you would rather split the cost while you decide.
What we would not recommend is ordering two sizes of a full tracksuit to compare. The sizing is consistent enough that it is not necessary, and it ties up money for a week.
Quick answers
Do ASICS tracksuits run small?
No. The Core range is true to size. If you have read otherwise, that advice was probably about a different brand or an older range.
Should I size up in an ASICS tracksuit?
Only the jacket, and only if you want to wear a hoodie underneath. Leave the pant at your normal size.
Can I buy the jacket and pant in different sizes?
Yes, and plenty of people do. Buy them as separates if the set only comes in matched sizes.
How do the shorts lengths compare?
5in sits above the knee, 7in sits closer to it. Both are true to size at the waist. It is purely about how much leg you want on show.
Is the ASICS Core pant slim or baggy?
Straight with a slight taper. It is neither. It sits cleanly on a trainer without clinging to the calf.
Prices correct at time of writing.