House-flies, Musca domestica, are carriers of more than 100 devastating diseases that have severe consequences for human and animal health. A key bottleneck to progress in controlling the devastating human diseases transmitted by house-flies is lack of knowledge of the basic molecular biology of this species. However, before sequencing of the house-fly genome can be seriously considered it is important to know the size of the genome. In this paper, we used quantitative real-time polymerase chain reaction to calculate genome size of the house-fly in side-by-side experiments with Drosophila melanogaster (known genome size of 180 Mb). Our results indicate the size of the house-fly genome is 295 +/- 10 Mb and that of D. melanogaster is 184 Mb. Thus, the house-fly genome is only about 1.6-fold larger than the genome of D. melanogaster. This indicates that the size of the house-fly genome makes it an excellent candidate for whole genome sequencing and that quantitative real-time polymerase chain reaction is an accurate method for the estimation of the size of insect genomes.