Aim: To evaluate the accuracy and precision for assessing fluid intake by examining the ability of nurses, patients and healthy people to visually estimate fluid volumes, thereby reflecting the fluid monitoring process in clinical practice.

Design: A cross-sectional study.

Methods: This study used the convenience sampling method and involved twenty-five participants from three groups; nurses, patients and healthy people. The participants carried out a set of different visual volume assessments of two types of fluids using two fluid containers. The exact volumes were measured, and the results were compared with the target volumes.

Results: High variations were observed in the fluid volume assessments for patients, nurses and healthy persons and also were observed to be an effect of environmental factors (fluid container or fluid type) on volume perceptions. This highlights the importance of finding new and innovative ways of measuring fluids for oral intake in a hospital setting, to ensure accurate and reliable data on fluid balance and thereby increase patient safety.