A rash guard only does its job when it fits like a second skin. Too loose and it bunches, rides up, and gives your opponent something to grab. Too tight and it restricts your breathing and movement. So how tight should a rash guard fit? This guide breaks down the ideal compression fit, a size chart by chest and weight, and how fit differs between long sleeve and short sleeve cuts.
How Tight Should a Rash Guard Be?
A rash guard should feel snug and compressive — like a firm hug around your torso, not like a regular t-shirt. You should be able to take a full deep breath and move your shoulders through a complete range of motion (think: reaching overhead, shrimping, bridging) without the fabric pulling, gaping, or riding up.
The quick test: pinch the fabric at your side. If you can grab more than an inch of loose material, the rash guard is too big. If the seams dig into your armpits or you feel restricted breathing, it's too small.
Rash Guard Size Chart
Rash guards use standard alpha sizing. Match your chest measurement and weight to find your starting size:
| Size | Chest | Weight |
|---|---|---|
| S | 34" – 36" | 130 – 150 lbs |
| M | 36" – 38" | 150 – 170 lbs |
| L | 38" – 41" | 170 – 190 lbs |
| XL | 41" – 44" | 190 – 215 lbs |
| 2XL | 44" – 47" | 215 – 240 lbs |
| 3XL | 47" – 50" | 240 – 270 lbs |
Chest is the primary measurement — weight is a helpful backup. If your chest and weight point to different sizes, go with your chest size.
How to Measure Your Chest
Wrap a soft tape measure around the fullest part of your chest, just under your armpits, keeping the tape level across your back. Breathe normally — don't puff your chest out or suck in. Take the measurement in inches and match it to the chart above. No tape measure? A piece of string and a ruler works just as well.
Long Sleeve vs Short Sleeve Fit
The torso fit is identical between long and short sleeve rash guards — the difference is in the arms. A long sleeve should run snug from shoulder to wrist with no bagging at the elbow; the cuff should sit at or just past your wrist bone. A short sleeve should end mid-bicep with an arm opening that stays put when you raise your arms overhead. If a short sleeve rides up into your armpit during rolls, try a size down.
What If You're Between Sizes?
- Prefer maximum compression? Size down. Grapplers who like a locked-in feel — especially competitors — often go one size smaller than the chart suggests.
- Prefer comfort for long sessions? Size up. The fit will be closer to a fitted athletic shirt than true compression.
- Broad shoulders, narrow waist? Size to your chest and shoulders; a slightly looser waist is normal and won't affect performance.
- Competing? Size down. A competition rash guard should be as close to the body as possible — loose fabric is a liability.
Will My Rash Guard Shrink?
Barely. Quality rash guards are made from polyester and spandex blends, which hold their shape far better than cotton. Expect minimal shrinkage — maybe a touch after the first hot wash. Wash cold and hang dry to keep the compression fit and printed graphics looking sharp for years.
Shop Rash Guards
Now that you know your size, check out our BJJ rash guards — premium compression-fit tops in long and short sleeve, built for the mats at $69.
Rash Guard Fit FAQ
Should a rash guard be tight or loose?
Tight and compressive. It should move with your skin, not slide over it. Loose rash guards bunch up, cause mat burn where they wrinkle, and give opponents grips.
Do rash guards stretch out over time?
Quality polyester-spandex blends keep their compression for a long time. Cheap rash guards with low spandex content can bag out — look for at least 10–15% spandex.
What size rash guard for a 6'0", 185 lb man?
Start with large (38"–41" chest, 170–190 lbs). If your chest measures over 41", go XL.
Can I wear a rash guard under my gi?
Absolutely — most grapplers do. It reduces friction, wicks sweat, and adds a layer of hygiene. Just make sure it fits snug so it doesn't bunch under the gi jacket.