You buy by the case. The recipe calls for pounds, ounces, cups or eaches. The guest gets a portion. Costing a recipe is just the walk from the first to the last.

Read the purchase as it arrives

Write down the case price, how many packs, the pack unit and what the product actually is, all in one place. A case described as “4 × 5 lb” is a 20 lb purchase, but only if all four packs contain the same ingredient and weight.

Use a common unit before you compare or divide:

Purchase unit cost = case price ÷ total purchase quantity

For an illustrative 20 lb case of onions at $24:

$24.00 ÷ 20 lb = $1.20 per purchased lb

Apply usable yield

The skins are in the case price, but they are not on the plate. If trimming leaves 85% usable product:

Usable quantity = purchased quantity × yield
20 lb × 0.85 = 17 lb usable

Cost per usable lb = case price ÷ usable quantity
$24.00 ÷ 17 lb ≈ $1.41 per usable lb

Use the yield for the product you actually buy and the way you actually prep it. Peeled, whole, roasted and drained canned onions won’t necessarily share a yield, or even a unit.

Cost the amount used by the recipe

If the recipe uses 6 usable pounds:

Recipe line cost = usable unit cost × recipe quantity
$1.4118 per usable lb × 6 lb ≈ $8.47

Carry every decimal while you work and round once, at the end. Round at every step and the pennies start to show across a few hundred portions.

Divide by the yield of the recipe

If the finished recipe produces 24 portions:

Portion cost = recipe cost ÷ finished portions
$8.4706 ÷ 24 ≈ $0.35 per portion

A sub-recipe works the same way. Cost the whole batch, write down what it yields, and the recipe that uses it takes only what it needs.

Stop when the units do not connect

If the unit you buy in and the unit the recipe uses don’t connect, don’t force it. A bottle priced by each and a recipe measured in fluid ounces needs the bottle volume. A bunch used as grams needs a measured bunch weight. Until you have that number, leave the gap where you can see it. Don’t quietly treat the two units as the same.

Keep the chain open

The trail is short:

Case price → purchase unit → usable yield → recipe quantity → batch yield → portion cost

When a case price or a yield changes, you fix that one link instead of rebuilding the recipe from memory.