The performance of a box-type solar cooker can be represented in terms of two figures of merit, F-1 and F-2. The second figure F-2 is a controlling factor in the sensible heating of a load. The present work validates F-2 by computing this figure from experimental data by two different procedures and comparing the results. An attempt has also been made to provide some guidelines for selecting a suitable temperature interval for determination of F-2. The results of some experiments to study the effect of number of pots and the load on F-2 have also been presented. It is recommended that for standardization tests should be conducted at full load.