Calculating the dosage of THC in your infused store-bought gummies can be challenging, as you may not know the exact concentration of THC in the oil or tincture you used. However, you can estimate the dosage by dividing the total amount of THC in the oil or tincture by the number of gummies you made. For example, if you used 1000mg of THC oil to make 50 gummies, each gummy would contain approximately 20mg of THC.