Pressure loss coefficients for laminar flow regime in solar collectors are mostly obtained using experimental study because they are not found in literature. This paper presents a mathematical model for estimation of pressure loss coefficients in tee junctions, which is an important part of the solar collectors, that incorporates Reynolds number and discharge ratios. Experimental data under solar collector standard testing conditions for pressure loss coefficients in tee junctions has been obtained and based upon it, nonlinear least squares optimization has been done to develop the equations for calculations of pressure loss coefficients for dividing and combining flows in tee junctions. The model developed exhibits reasonable accuracy to experimental results.