How to Build a Simple Grocery Price Book

One line per item, each price in one fixed unit. Four columns are enough:

The last column is your own target: a price that is good enough to stock up on non-perishables. You set it after watching prices for a few weeks.

A sign says your cereal is “Was $5.49, now $4.49!” for a 15 oz box.

1. Price per ounce: $4.49 ÷ 15 ≈ $0.299.
2. Price per pound (the unit in your book): $0.299 × 16 ≈ $4.79.
3. Your book says you usually pay $4.49 per pound, and your target is $3.75.
4. This “sale” is more expensive per pound than your normal price. Skip it.

The sign compared the sale with the old price of this box. Your book compares it with what you actually pay. Use the calculator below to convert any shelf price into your book’s unit.

Chicken thighs are on sale at $1.89 per pound. Your book: usually $2.49, best seen $1.79, buy at or below $1.99.

1. $1.89 is below your $1.99 target, so it is a good price.
2. It is about 24% below your usual price: ($2.49 − $1.89) ÷ $2.49.
3. Buy what you will cook or freeze in the next few weeks — this is the moment to stock up.

1. Pick 15–25 items you buy often. Staples and big-ticket items matter most: coffee, meat, cereal, detergent, toilet paper, diapers, pet food.
2. Choose one unit per item and stick to it: per lb or per kg for food sold by weight, per fl oz or per liter for liquids, per item, sheet or load for counts.
3. Record today’s price at your usual store: the date, the store, the size and the price per unit.
4. Each time you shop over the next month or two, update the “best price seen”.
5. Set your “buy at or below” price slightly above the best price you have seen.

A notebook, a spreadsheet or a notes app all work. Tip: after a comparison on this site, the address bar contains your prices and sizes — save or bookmark the link to keep it.

Packages change size, and stores label the same item in different units. If your book says coffee is “$9.99”, you can’t compare it with a different bag next time. “$11.99 per lb” always works, whatever the bag size. The price per ounce, price per kg and cost per item calculators convert any package to your chosen unit in seconds.

• Which “sales” are real — and which are just the normal price with a red sign.
• How often your items go on sale, so you can buy enough to last until the next one.
• Whether a warehouse club or another store is actually cheaper for your basket — see is Costco really cheaper?
• Shrinkflation: if the price per unit creeps up while the shelf price stays the same, the package got smaller. The shrinkflation calculator shows by how much.
• Whether multi-buy offers beat your target — see BOGO vs. percent off.

A price book also answers the bigger question — which store to use. Compare your usual weekly quantities at two stores:

Store B is $1.70 cheaper for this basket even though its pasta costs more. Over a year that is about $88 — worth knowing, without having to guess.