There is no single correct number of cans or months of food for every home. Calculate an amount for each food you use regularly.
Measure use and choose coverage
Note how many packages you use in a normal week or month. Choose how long you want the supply to last, considering shopping frequency, shelf space, package size, and money tied up in groceries.
Amount used per month × months of coverage = target amount.
If you use four cans of tomatoes a month and choose two months of coverage, your target is eight cans. With three already on hand, you need five to reach it. That is a target to work toward, not an instruction to buy immediately.
Set a shopping trigger
The target is the amount after restocking. The minimum is the amount that prompts you to put an item on the shopping list. Set minimums for staples whose absence would interrupt meals; an occasional ingredient may need no reserve.
Check package size and real cost
A larger package is useful only if you can store and finish it in good condition. Compare unit prices, but count any waste and the cost of storage. If your planned target will not fit, reduce it or prioritize fewer foods.
After a shopping cycle, compare the estimate with what you used. Raise or lower one target at a time.
Related guides: The Beginner Pantry Checklist: What to Keep and What to Skip · How to Keep a Simple Pantry Inventory · How to Separate Open Stock From Pantry Backstock