# If I only know the mass of one sample of food with a certain amount of Calories, how can I know how many more Calories a larger sample of the same food has?

Calories per gram ($\text{Cal/g}$) implies calories per gram associated with those calories.
A change-in-food mass is associated with the $\text{Cal/g}$ units, and just like a change in position in $\text{m}$ can be determined from the velocity in $\text{m/s}$, you need a change-in-food mass to determine the analogy to velocity, the calories-per-gram.