There is no general answer to this question. It depends entirely on the type of wood and the length of the material to be split. Simple models have a splitting pressure of four to eight tons.
If you only want to split blocks of wood with a relatively short length into logs for your fireplace, a pressure of six tons is absolutely sufficient. For hardwoods it may be a little more.
Devices with more than twelve tons are real powerhouses that are suitable for professional forestry work.