converting mg to ml with weight of animal in kg

I am having such a hard time with converting a drug in mg/ml to ml in order to give to an animal. For example if giving 100mg of 4%lidocaine 40mg/ml to a 156lb (71kg) to an animal. how much ml is that??? Can anyone give me an easy formula to figure all this out?

I am having such a hard time with converting a drug in mg/ml to ml in order to give to an animal. For example if giving 100mg of 4%lidocaine 40mg/ml to a 156lb (71kg) to an animal. how much ml is that??? Can anyone give me an easy formula to figure all this out?

I think the weight is irrelevant here. Sometimes doses are weight-related and stated mg/kg (you would multiply the dose instruction by the animal's weight), other times they are an absolute dose in mg.

To give a absolute dose, 100 mg, divide by the strength 40 mg/mL. Dose is 2.5 mL

As an alternative, you can write the strength inverted and multiply:
100 mg x 1 mL/40 mg = 2.5 mL (note how the mg terms cancel out)