Calculating Cost per Ounce and per Serving
Cost per ounce and per serving is the building block of every recipe cost. Here's how to convert any purchase unit into a per-serving cost, with worked examples.
To calculate cost per ounce, divide the purchase price by the number of ounces in the package; to get cost per serving, multiply that by the ounces in one portion. This simple conversion is the foundation of all recipe costing — you buy in cases and tins, but you plate in ounces and each, so every accurate plate cost starts here.
The two formulas
Cost per unit = Purchase price ÷ Units per package
Cost per serving = Cost per unit × Units per serving
The trick is getting everything into the same unit. Convert the package size into the unit your recipe uses (ounces, grams, each), then divide.
Worked examples
Olive oil: a 3-liter tin costs $18. Three liters is about 101.4 fluid ounces. Cost per ounce = $18 ÷ 101.4 = $0.178/oz. A 2 oz pour = $0.36.
Chicken breast: a 40 lb case costs $112. That's 640 oz. Cost per ounce = $112 ÷ 640 = $0.175/oz. A 6 oz portion = $1.05.
| Item | Package | Price | Cost/oz | Serving | Cost/serving |
|---|---|---|---|---|---|
| Olive oil | 101.4 oz | $18.00 | $0.178 | 2 oz | $0.36 |
| Chicken | 640 oz | $112.00 | $0.175 | 6 oz | $1.05 |
| Parmesan | 80 oz | $33.60 | $0.420 | 1 oz | $0.42 |
Don't forget yield
Cost per purchased ounce isn't the same as cost per usable ounce. If an item has trim or shrink, divide by its yield to get the true cost — see yield testing. A protein at $0.175/oz with a 75% yield really costs $0.233 per usable ounce.
Master the unit conversion and recipe costing becomes arithmetic. Get it wrong and every plate cost built on it is wrong too.
Let the conversions happen automatically
Doing these conversions by hand for hundreds of ingredients is where costing stalls. Cobblestone POS stores each ingredient's purchase unit and recipe unit and does the conversion for you, so plate costs stay accurate and update when invoice prices change. Daisy, its AI assistant, keeps costs current from vendor invoices. It's a free, all-in-one platform for independents; owners leave pricier systems like Toast ($470+/month) because this costing is built in. This feeds straight into costing out a recipe.
Frequently asked questions
How do I convert liters or kilos to ounces? One liter ≈ 33.8 fluid ounces; one kilogram ≈ 35.3 ounces. Multiply the package size, then divide the price by the total ounces.
Should I use purchased or usable cost? Usable, whenever there's trim or shrink. Divide the per-ounce cost by the yield percentage to get true cost per usable ounce.
Cost per ounce or per gram? Use whatever unit your recipes are written in and stay consistent. Mixing units is the top source of costing errors.
The bottom line
Every accurate plate cost starts with a clean unit conversion, and every menu price you trust is built on top of it. Master the two formulas, stay consistent with your units, and adjust for yield, and recipe costing stops being intimidating and becomes simple arithmetic. Get this building block right and everything downstream — plate costs, menu prices, and food cost targets — finally rests on solid ground.
Common questions
Should I cost by weight or volume? By weight for anything solid and by volume for liquids you actually pour. Mixing the two, like costing cheese by the cup, is how most portion costs end up wrong.
How do I handle items sold in odd pack sizes? Convert the whole case to ounces first, then divide by the number of ounces in one serving. Write the per-ounce figure on the recipe card so nobody redoes the math.
Convert any unit with the free Cost-per-Unit Calculator (Excel).
