The opening is 1 inch wide. That said, it really depends on what you are cutting. It cuts through soft wood, e.g. pine, like butter. For hard woods, or shrubs like privet I would say 3/4 of an inch for one clean cut, or two cuts at the same spot if it is 1 inch. One thing to be careful of, if you bite off more than you can chew it will get stuck and you have to wrestle it out. That isn't too bad if you are on the ground, but if you are reaching up high or at an awkward angle be careful of biting off more than you can chew. I know 3/4 of an inch doesn't sound that great, but it is amazing how much you can get done between 3/4 - 1 inch. This is especially true once you have a little experience using the lopper. Cheers, Bill -//-