The supplier sells a case. The recipe uses pounds, ounces, cups, or eaches. The guest receives a portion. Recipe costing is the path between those three facts.

Read the purchase as it arrives

Record the case price, pack quantity, pack unit, and the ingredient identity together. 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

Yield should describe the product and preparation you actually use. Peeled onions, whole onions, roasted onions, and drained canned onions do not necessarily share a yield or unit path.

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

Keep full precision while calculating and round the displayed result at the end. Rounding every intermediate conversion can create small differences that become noticeable across many 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

For a sub-recipe, the same logic applies. Cost the whole batch, record its finished yield, then let the parent recipe use only the quantity it needs.

Stop when the units do not connect

Do not force a result when the purchase and recipe units cannot be reconciled. 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. Missing conversion evidence should leave a visible gap rather than silently treating unlike units as equal.

Keep the chain open

The useful audit trail is short:

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

When the supplier price or yield changes, you can revisit the affected link instead of rebuilding the recipe from memory.