Based on Davies' group contribution method, hydrophile-lipophile balance (HLB) values were calculated by effective chain length (ECL) instead of actual chain length of straight alkyl chain. polyoxyethylene (EO) chain, and polyoxypropylene (PO) chain. Linear equations were adopted for the effective chain length of straight alkyl chain and PO chain; a Gamma probability density function (PDF) was used to describe the contribution of each EO group to HLB and the effective chain length of EO chain Could be obtained by integrating Gamma PDF The HLB values of 224 nonionic surfactants were calculated and the average absolute error is less than 1.5, which is much better than the results obtained by Davies. (c) 2005 Elsevier Inc. All rights reserved.