The effect of boundary conditions (e.g., type of metal contacts) and sample geometry (e.g., sample aspect ratio) on measurements of direct longitudinal d(33) coefficient in piezoelectric ceramics is studied by direct quasistatic method. We show that at small aspect ratio (thickness/lateral dimension <0.1) the measured d(33meas) is as much as 30% lower than the true value, d(33true). Measured d(33) increases with increasing aspect ratio and reaches its true value at a threshold aspect ratio that is dependent on ceramic composition and is about approximate to0.5 in the case of soft and hard Pb(Zr,Ti)O-3. Experimental results show that, when the force is applied over the whole electroded surface of the sample, the d(33) depends only on the aspect ratio and not size of samples. The experimental results are compared with simulations using finite element modeling (FEM) and are interpreted in terms of distribution of strain/stress within the sample, which leads to functional dependence of the measured d(33) on transverse d(31) and shear d(15) coefficients. It is shown experimentally and by FEM that the value of d(33) at low aspect ratios depends on the type of metallic contacts used to collect the charge and apply the pressure on the sample. Effect of nonlinearity of the d(31) and d(15) coefficients on d(33) measurements also is considered.