block ram area equivalent in logic elements , Cyclone iv

For the present example, the comparison doesn't make much sense. Nobody would replace a dual port memory by registers, except as a mistake. It's more interesting if register banks are replaced by small sclices of block memory. In this cases, RAM blocks are often only partly populated but can still save a lot of overall FPGA resources. Due to this partial utilization, calculating LE equivalents misses the point.