This paper presents a general criterion to classify a channel as micro-channel or macro-channel. Experimental results of saturated-flow boiling heat transfer in micro/mini-channels for both multi- and single-channel configurations were obtained from the literature. The collected database contains 4228 data points, covering a wide range of working fluids, operational conditions. and different micro-channel dimensions. Seven existing correlations were evaluated against the database to verify their respective accuracies. A combined non-dimensional number Bo (*) Re-1(05) = 200 was introduced as the new conventional-to-micro/mini-channel criterion In addition, a generalized prediction method was proposed based on the new criterion, with accurate predictive capability. (C) 2009 Elsevier Ltd. All rights reserved