In regards to nozzle size there is one universal principle. This is the fact that if you half the size of the nozzle in diameter, the pressure of the jet stream will double, likewise if you double the size of the nozzle, there will be double the pressure.
This principle should help you determine the type of gun you’d want to purchase And there are 4 settings of pressure washing nozzles:
The 0 degree nozzle shoots a straight jet of water directly on to the surface without causing a fan effect. Purely a stream.
The 15 degree nozzle hits the target with a wider surface area, there fore creating a slight sheet of water. Because the force is spread across a larger area.
The 25 creates an even larger sheet or fan due to having less pressure than the 15.
The 40 degree is the most gentle and wisest spread perfect for cleaning down a window.