Combat sports sizing does not follow ordinary clothing sizing: a gi runs on its own A-scale, gloves are sold by weight rather than fit, and a rash guard is meant to be tighter than any shirt you own. This is how to pick each one.
Gi sizes run A0 to A4 and are driven by height first, build second. A0 suits roughly 5'2"–5'5", A1 5'5"–5'8", A2 5'8"–5'11", A3 5'11"–6'2", A4 6'2"–6'5", with heavier builds sizing up within an overlap rather than across two sizes.
Buy for the height band and expect shrinkage: cotton gi fabric loses a little length in the first few washes, so a gi that is marginally long out of the bag is usually right after a month. Sleeves should end at the wrist bone with the arm extended, and trousers at the ankle.
A rash guard is compression wear, not a t-shirt. It should be tight enough that it does not gather when someone grips it and does not ride up in a scramble. If you are between sizes, size down rather than up — a loose rash guard defeats the point of wearing one.
Spats size the same way. A matched set is sized as one: take the size that fits your torso and the bottoms will follow.
Fight shorts are sold on waist measurement in inches, not S/M/L, and they sit on the hip rather than the natural waist. Measure where you actually wear shorts. If you are between two sizes, take the larger — a fight short that is a fraction loose still works with the closure system, and one that is a fraction tight restricts the exact range of motion it exists to allow.
Muay Thai shorts are cut deliberately wider and shorter through the leg to allow high kicks and knees. They will look larger than a fight short in the same waist size; that is the design, not a sizing error.
Boxing gloves are sold by ounce, which is padding weight rather than hand size. The ounce you want depends on what you are doing, not how big your hands are: 6 oz for speed and competition, 8–10 oz for pad and bag work, 12 oz as a general training weight, and 14–16 oz for sparring, where the extra padding protects your partner rather than you.
MMA gloves are open-palm and sized S/M/L on hand circumference measured around the knuckles, excluding the thumb. They should be snug enough that the padding stays over the knuckle when you make a fist.
Shin guards size on height and calf circumference together; the guard should cover from just under the knee to the top of the foot without the instep pad sliding under the arch. Headgear sizes on head circumference measured just above the eyebrows.
Wrestling singlets size on height and weight together and are meant to be close-fitting throughout, with no slack at the shoulder or the leg opening.
Every product page lists the sizes that item is offered in and what it is built for. If you are between sizes on something specific, contact us with the product name and your usual size in a brand you already own — that comparison is far more useful than measurements alone.