How did you calculate the conversion factor?

A serial dilutions of HEK293, CHO, and E. Coli gDNA standard test them using HEK293, CHO, and E. Coli ResDNA Quant Kits, respectively. We then compare the copies per microliter obtained at different loading concentrations. We correlate the number of copies of target amplicon with the loading amount in picogram. To rule out any issues with PCR performance, loss of target amplicons, loading errors, user error, instrument errors, etc. skewing the true conversion factor, we repeat the testing over multiple samples, multiple batches of kits, standards, and multiple users. This gives us our accurate conversion factor.