As a general rule, the diameter of the orifice for the abrasive nozzle should be approximately three times the water nozzle orifice.

Some people would suggest using a smaller ratio, about 2.5 times. Using a smaller ratio does produce faster cutting speeds. The trade-off is increased nozzle wear and costs. Part tolerance will suffer because of the increased speed of nozzle wear.

Following is a quick reference guide for the most common orifices for abrasive waterjet cutting. Typical abrasive amounts and water flow are also shown for easy reference.