Forklifts are rated according to how much weight they can lift.
The size of your typical load will affect the capacity you need. Forklift capacity is usually based on a 600 mm "load centre", meaning that the distance from the centre of gravity to the sides of the load is 600mm.
The easiest way to think about this is that a forklift can only lift its maximum weight if the load is 1200 mm across. If your loads are unusually long or high, the forklift won’t be able to safely lift as much. Knowing the typical dimensions and weight of your loads will allow us to advise you on the exact capacity you need.
Also consider how much variation there is in your loads. If you constantly produce identical pallets of products, you know exactly what capacity you need. However, in a more mixed environment, or one where the load size changes over time, you may want to buy a forklift with more capacity than you need currently to make sure it gets the job done now and in the future.