The modern era of embedded system design is geared towards design of low-power systems. One way to reduce power in an ASIC implementation is to reduce the bit-width precision of its computation units. This paper describes algorithms to optimize the bit-widths of fixed point variables for low power in a SystemC design environment. We propose an algorithm for optimal bitwidth precision for two variables and a greedy heuristic which works for any number of variables. The algorithms are used in the automation of converting floating point SystemC programs into ASIC synthesizable SystemC programs. Expected inputs are profiled to estimate errors in the finite precision conversions. Experimental results on the trade-offs between quantization error, power consumption and hardware resources used are reported on a set of four SystemC benchmarks that are mapped onto 0.18 micron ASIC cell library from Artisan Components. We demonstrate that it is possible to reduce the power consumption by 50% on average by allowing round-off errors to increase from 0.5% to 1%.