Several efficient counters are presented. A nine-transistor divide-by-two circuit is used as a basic building block. With transistor sizing, an input frequency of 400 MHz can be adopted by an asynchronous counter, while an eight-bit synchronous counter can achieve clock rates of more than 200 MHz in a 3μm CMOS process. The power consumption of the proposed precharged dynamic synchronous counter is reduced to almost half as much as normal.