We have developed a new protocol for using Molecular Inversion Probes (MIP) to accurately and specifically measure allele copy number (ACN). The new protocol provides for significant improvements including the reduction of input DNA (from 2?g) by more than 25 fold (to 75ng total genomic DNA), higher overall precision resulting in one order of magnitude lower false positive rate, and greater dynamic range with accurate absolute copy number up to 60 copies.