The accurate measurement of reflectance and transmittance properties of materials is essential in the printing and display industries in order to ensure precise color reproduction. In comparison with reflectance measurement, where the impact of different geometries (0°/45°, d/8°) has been thoroughly investigated, there are few published articles related to transmittance measurement. In this work, we explore different measurement geometries for total transmittance, and show that the transmittance measurements are highly affected by the geometry used, since certain geometries can introduce a measurement bias. We present a flexible custom setup that can simulate these geometries, which we evaluate both qualitatively and quantitatively over a set of samples with varied optical properties. We also compare our measurements against those of widely used commercial solutions, and show that significant differences exist over our test set. However, when the bias is correctly compensated, very low differences are observed. These findings therefore stress the importance of including the measurement geometry when reporting total transmittance.