The Cooling Tower Institute has adopted much needed guidelines for providing meaningful estimates of measurement uncertainty and the propagation of these uncertainties into the determination of cooling tower capability. Uncertainty analyses can be useful in determining test validation and compliance with contractual agreements. This paper addresses actual and desired uncertainties associated with specific test parameters. It addresses how these errors propagate into the calculation of cooling tower capability uncertainty. Specific examples are given based on multiple hours of test data acquired on both natural draft (crossflow and counterflow) and mechanical draft (rectangular and circular) cooling towers. The paper will show how significant uncertainty is calculated versus predicted capability in natural draft cooling towers can occur. Guidelines for reducing uncertainty are provided for mechanical and natural draft towers.