Portion costing is where theoretical food cost meets reality. Your recipe says 6 oz of protein per plate. Your line cook plates 7 oz. That single ounce, multiplied across 150 covers a night, costs you $40–$70 a shift. Over a year it is the difference between a healthy operation and a slow bleed. This guide shows you how to calculate cost per portion accurately and control it on the line.
What Is Cost Per Portion?
Cost per portion is the actual food cost of a single plated serving as it leaves the kitchen. It includes the protein, starch, vegetable, sauce, and garnish that make up the final dish — weighed and measured at the portion size your kitchen actually plates.
It is distinct from cost per serving (which is based on the recipe yield) and from theoretical food cost (what the dish should cost if everything were plated perfectly). Cost per portion is the real number.
The Cost Per Portion Formula
Cost Per Portion = Σ (Ingredient Portion Weight × Cost Per Unit)
For each component of the plated dish, multiply the portioned weight by the cost per unit, then sum. Simple arithmetic — the hard part is measuring accurately.
Worked Example: Grilled Salmon Plate
Grilled Salmon with Rice Pilaf and Asparagus
- Salmon fillet (6 oz portion @ $1.40/oz): $8.40
- Rice pilaf (4 oz @ $0.22/oz): $0.88
- Asparagus (3 oz @ $0.38/oz): $1.14
- Lemon butter sauce (1 oz @ $0.45/oz): $0.45
- Herb garnish: $0.12
- Cost per portion: $10.99
At a 32% target food cost, this dish should be priced at $10.99 ÷ 0.32 = $34.34. Most restaurants would round to $34 or $35.
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Why Portion Size Control Matters More Than You Think
Most restaurants use weight-based portioning for proteins (the highest-cost ingredient) and volume-based portioning for starches and vegetables. Every ounce over spec on a $1.40/oz protein is $1.40 straight out of your margin. Scale that across a busy night:
The True Cost of Over-Portioning
- Recipe portion: 6 oz of chicken breast
- Actual line portion: 7 oz
- Over-portion per plate: 1 oz = $0.48 (at $7.70/lb)
- Plates per night: 120
- Nightly waste: $57.60
- Annual waste (6 nights/week): ~$17,950
That $18,000 is pure lost margin. It does not require better ingredients, a bigger kitchen, or more customers. It requires a scale on the line and a culture of using it.
Tools for Portion Control on the Line
- Digital scales. One per station for all proteins. Under $30 each.
- Portion scoops. Numbered scoops give consistent volume for starches, salads, and sauces.
- Ladles. Labeled ladles for sauces and soups make spec portions automatic.
- Plate diagrams. Visual references by the pass show correct plating. Especially useful for new cooks.
- Yield testing. Regularly weigh raw vs. cooked portions to catch recipes that drift.
Yield and Trim: The Hidden Portion Cost
Raw product does not equal plateable product. A whole chicken breast weighs 8 oz raw, but after trimming and cooking yields maybe 5.5 oz of plateable protein. If you buy 100 lb of chicken breast at $4.00/lb and your usable yield is 70%, your effective cost per oz is $0.36, not $0.25.
Effective Cost Per Oz = Purchase Price ÷ (Total Weight × Yield %)
For any protein, do yield testing before setting portion costs. A 10% miscalculation on yield translates to a 10% error in every portion cost for that item. Over hundreds of covers that error compounds quickly.
The Portion Cost Card
Every menu item should have a portion cost card on file with:
- Every ingredient and portion weight
- Cost per unit at current prices
- Total cost per portion
- Menu price and food cost percentage
- Last updated date
Portion cost cards are the reference a manager uses during a quarterly menu review to decide what to keep, re-engineer, or retire. Our menu engineering guide covers how to use these cards systematically.
Actual vs. Theoretical Cost Per Portion
Your theoretical cost per portion is what the recipe says it should cost. Your actual cost is what you see in your P&L after inventory and usage accounting. The gap between the two reveals problems:
- Over-portioning (covered above)
- Waste and spoilage
- Theft or unauthorized consumption
- Inaccurate recipes or portion specs
- Price changes not reflected in theoretical cost
A healthy operation runs 2–4% gap between theoretical and actual. A 6% or higher gap means you have a specific, findable problem worth investigating.
What to Do This Week
- Pick your top-5 menu items by volume.
- Calculate current portion cost for each using a free calculator.
- Weigh a sampled plate of each during service to compare spec vs. actual.
- Update prices on any item with a food cost percentage above 35%.
- Put scales on the line and train cooks to use them.
Price Your Recipes with Confidence
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