The　2D　top　view　of　the　droplet　formation　in　microfluidic　T-junction　devices　with　a　neck　is　recorded　to　estimate　the　droplet　volume　under　different　flow　conditions.　The　channel　with　a　neck　at　the　T-junction,　to　provide　a　narrow　structure,　is　proposed　but　has　not　been　analyzed　as　the　normal　T-junction.　The　droplet　generation　process　is　separated　into　two　stages,　including　the　filling　stage　and　the　squeezing　stage,　to　develop　a　droplet　size　predictive　model　based　on　the　continuity　of　both　liquids.　In　a　wide　range　of　flow　conditions　for　multiphase　microfluidics,　this　study　validates　and　physically　explains　the　model　by　analyzing　the　generation　of　droplets　and　coefficients　of　the　model.　Results　of　this　study　can　help　to　design　droplet　microfluidic　devices,　where　it　is　requisite　to　know　the　relation　between　flow　conditions　and　the　droplet　size.