Beginner roller skating
How to Size Roller Skates (Don't Guess Your Shoe Size)

Most beginner pain comes from a bad fit, not from falling. Measure in millimetres, check the brand's own chart, size snug - never loose.
Most beginner pain comes from a bad fit, not from falling. Blisters, numb toes and heel lift are all sizing problems wearing a disguise.
Measure your foot in millimetres, heel to longest toe, standing, at the end of the day when your feet are at their largest. Then read the brand's own chart — skate sizing is not shoe sizing and it varies wildly between makers.
Aim for snug: toes brushing the end, zero heel lift when you rise onto the ball of your foot. A skate you can wiggle in is a skate you cannot steer.
Keep going: this is one section of the full Roller Skating for Beginners guide — sizing, gear, stopping, and where to skate, in one page.