This paper proposes a common performance parameter for different solar cooker types in place of different performance parameters hitherto being used for each type. The performance parameter called cooker opto-thermal ratio (CUR) is based on the Hottel-Whillier-Bliss (HWB) equation and may be experimentally determined using a corresponding single step test procedure proposed here. The protocol for the test procedure has been formulated carefully so as to make it common for all cooker types. To establish its utility in inter-cooker comparison two cooker types viz. Box-type (BC) and concentrating type (CC) were tested initially. The mean value of cooker opto-thermal ratio for concentrating type and box type was found to be 0.155 and 0.136, respectively, clearly depicting the superior performance of concentrating type. (C) 2012 Elsevier Ltd. All rights reserved.