BEMLAB [1] is the open source project implementing Boundary Element Method (BEM) [2,3] comprehensively. BEMLAB binary packages and the source code are distributed under GNU LGPL (Lesser General Public License) license terms. The project provides universal library and the reference application, which is the easiest way for solving problems using BEM. The article presents example BEMLAB application in modelling comb capacitors used in Micro-Electro-Mechanical Systems (MEMS). Finally capacitance will be calculated using BEM results. Particularly Asymptotic Boundary Conditions (ABC) will be used to model external space of the capacitor (the geometry of infinite half-lane) as an internal BEM problem. This approach will allow to calculate total capacitance with dispersed capacitance included. Results will be compared with the simplified model.