Pin accessibility influences the routability of a design at the stage of block/chip assembling. The estimation model for pin accessibility in previous researches counts the total number of intersections between each pin and M2 routing tracks. It does not consider the variation of pin accessibility as the spacing between a pin and its neighboring pins and metal wires changes. Besides, it cannot properly deal with the off-grid pin access neither. In this paper, we propose a general model for pin accessibility estimation. In the model, all directions to connect to the boundary of a pin are under estimation. Off-grid pin access is also available. Experimental results show that the reduction rate of minimum area to complete the routing of a circuit can be 7.0% on average. Due to the diminishment of required area for routing, the total number of vias for higher metal layer also decrease under the same area constraint.