This calculator uses the same planning rates as the rest of this section: 1 gallon of water per person per day from Ready.gov and the Red Cross, and a planning assumption of 2,000 calories per person per day, the general figure on U.S. Nutrition Facts labels (FDA). It is not a personal prescription. Needs vary by age and activity; see the USDA ranges on the food page. In very hot weather, Ready.gov notes that water needs can double, so treat the gallon as a floor.
The form starts from the “People at home” picker at the top of the page (4 people, entered as 2 adults and 2 children). You can change those numbers. Pets are optional and can be entered as small, medium, or large. Pet food is not given a calorie figure on this site, so it is not totaled here — pack several days of the food your animals already eat, as described on the pets page.
Other kit items such as a flashlight or headlamp for each person, or a power bank for each person who relies on a phone, are per-person counts rather than per-person-per-day rates. They are on the supply checklist and are not multiplied across 3 and 14 days here.