XXL ski knee pads are designed for knee circumferences of about 48-53 cm (roughly 19-21 inches), typically fitting the largest adults. If you've found that XL pads from most brands feel tight, dig into your leg, or leave deep marks after wearing them, XXL is likely your better option.
To confirm your size, measure around the center of your kneecap with your leg slightly bent — this mimics your knee position while skiing. If you're right at the boundary between XL and XXL, consider sizing up for comfort, especially if you'll be wearing the pads all day on the mountain. A pad that's too small can restrict circulation and become unbearable after a few runs.
Don't squeeze into a smaller size thinking it'll stay on better. A properly fitted XXL pad will stay put during falls — that's what the silicone grips and straps are for. Just make sure to check each brand's specific size chart, since XXL measurements can vary significantly between manufacturers.