A size Large in ski gloves typically fits a hand circumference of 8.5 to 9.5 inches, measured around the widest part of your palm (excluding the thumb). This size is most common for larger men, but hand shape varies, so measuring is really the only way to know for sure.
Getting the right size matters more than you might think. If your gloves are too tight, they restrict blood flow and your hands will actually get colder, no matter how much insulation the glove has. Too loose, and you lose warmth because the insulation can't trap body heat effectively. A Large should give you a snug but not squeezed fit, with a small air gap at the fingertips — that gap is what the insulation needs to work.
One common mistake is not accounting for liner gloves. If you wear a thin liner underneath, try the Large on with that liner in place. Also, sizing can vary between brands, so always check the specific brand's size chart rather than assuming your size carries over.