I am not an expert in this field, but I am very interested and have researched to find an answer. I received some assistance from tlooto.com for this response. Could you please review the response below to see if it is correct?

For purified rTaq with good activity and purity, the typical activity unit per µg can be estimated based on available data and standard practices in molecular biology. Generally, commercial Taq DNA polymerase preparations exhibit an activity of approximately 200 to 500 units per µg of enzyme, translating to 200,000 to 500,000 units per mg [1][2]. This range is consistent with the enzyme's performance in routine PCR applications, including genotyping. While precise activity measurements are ideal, this estimate should suffice for adjusting enzyme concentrations in your protocols, ensuring consistent performance without requiring exact activity assays [1][2].

Reference

[1] Jalali, H., Pourbakhsh, A., Fallah, F., & Eslami, G. (2015). Genotyping of Virulence Factors of Uropathogenic Escherichia coli by PCR. Novelty in Biomedicine, 3, 177-181.

[2] Kumar, P., Nagarajan, A. G., & Uchil, P. (2019). Calcium Phosphate-Mediated Transfection of Adherent Cells or Cells Growing in Suspension: Variations on the Basic Method.. Cold Spring Harbor protocols, 2019 10, pdb.prot095455 .

I don't measure activity in units making Taq, what I do is preform a test PCR reaction using several dilutions of the enzyme in order to find the one giving the best amplification. In most cases dilution of 20-50X was the one that worked.