Seirus Sizing
  Men's   S   M   L   XL
  Hand Length   8 3/8   8 3/8   8 1/2   9
  Knuckle Circumference     8 1/8     8 3/8     8 3/4     8 3/4  

  Women's   S   M   L
  Hand Length   7 7/8     7 7/8     7 7/8  
  Knuckle Circumference     7 1/8   7 3/8   8 3/8

Measurements stated in inches unless otherwise indicated.

Neck: Measure around the base of your neck. Or, simply find a collared shirt that fits you well. Lay the collar flat, and measure from the middle of the collar button around to the far end of the button hole.
Chest: Keeping your arms relaxed at your sides, measure under your arms at your armpits. Include the highest part of your chest and shoulder blades.
Sleeve: With arm relaxed at side and slightly bent, measure from the center back, across shoulder to elbow, and down to the wrist.
Waist: Measure at your natural waistline, where your belt normally rests.
Hips: Standing with your feet together, measure around the fullest part of your seat.
Inseam: Take a pair of pants that fit you well and measure along the seam from the crotch to the bottom of the leg.
Hand (for gloves): To measure knuckle circumference, keep your hand flat and measure around your large knuckles. Do not include your thumb. To measure hand length, measure from the base of your palm to the end of your middle finger.
Head (for hats & helmets): Measure around the largest part of your head, just above the brow.