Only a portion of the water content, known as Available Water, can be potentially taken up by the crop. This is dependent on the Soil Type.
How do I calculate Available Water?
Sprinkler Plus provides a default value for each soil type, and you can fine-tune it if you think it does not best describe the water storage capacity of your zone. Increasing the Available Water will increase the water amount for a single watering.
Learn more about your soil type in this article: How do I identify my soil type?