An irrometer is a direct measurement system, which means that it actually reads the physical forces at work in the soil. Irrometers act like a dummy root, allowing the soil moisture to interact with the instrument through the ceramic tip.

Soil water tension outside of the instrument tries to remove the water from it, which creates a measurable tension inside the column.​

It provides the user with accurate information on soil moisture status regardless of soil type

This tension is read with either a mechanical gauge or a transducer attached to the instrument.