These gloves are consistent with the major American based brands we carry such as FirstGear, Tour Master, Joe Rocket, etc, so hopefully you’ve had some experience with buying gloves and can choose based upon the fit of a previous pair. If you have no previous experience with glove sizing, go here for help.
Just as an FYI, you may have previous experience with European designed brands such as Alpinestars and REV’IT! which run about one half size smaller, size-for-size, than the American brands. It is not a universally true fact, but generally holds for most styles. So if a particular size in either of those brands is roomy on you, then you may be able to go down one full size in this style.