The Bond work index, W-i, is defined in a Bond ball mill on the samples of standard size -3.327 + 0 mm. In practice, it is possible to find materials of non-standard size that are finer than 3.327 mm. In this work, a procedure for the calculation of the Bond work index is suggested for cases when the Bond grindability test is conducted on samples of non-standard size. (C) 2012 Elsevier B.V. All rights reserved.