Dose means quantity (in units of energy/mass) in the fields of nutrition, medicine, and toxicology. Dosage is the rate of application of a dose, although in common and imprecise usage, the words are sometimes used synonymously.
https://en.wikipedia.org/wiki/Dose

The dose is the amount of drug taken at any one time. This can be expressed as the weight of drug (e.g. 250 mg), volume of drug solution (e.g. 10 mL, 2 drops), the number of dosage forms (e.g. 1 capsule, 1 suppository) or some other quantity (e.g. 2 puffs).
https://www.drugs.com/dosage/

dosage strength (1) The proportion of active drug substance to excipient, measured in units of volume or concentration.
(2) The strength of a drug product, which indicates the amount of active ingredient in each dosage.
http://medical-dictionary.thefreedictionary.com/dosage stren...