Every gram on the plate affects your bottom line. Too generous with portions? You're bleeding money. Too stingy? Customers walk away unsatisfied. The math behind portion sizing isn't complicated, but it requires precision.
Why portion size matters so much
Most kitchens eyeball portions. "A generous spoon" or "the usual amount" aren't standards. Reality check: your chef serves 250 grams of meat while your calculations assume 200 grams. Each portion costs you an extra €2.40.
⚠️ Note:
At 50 portions weekly, this inconsistency drains €6,240 annually from your profits. Pure waste.
The basics: calculating cost price per gram
You need the per-gram cost of every ingredient. Simple division gets you there.
💡 Example:
Beef tenderloin at €45 per kilo:
- €45 ÷ 1000 grams = €0.045 per gram
- 200 gram portion = 200 × €0.045 = €9.00
- 250 gram portion = 250 × €0.045 = €11.25
Difference: €2.25 per portion
Including trimming loss in your calculation
Whole products come with waste. A 2kg salmon yields only 1.1kg of fillet. Your real cost isn't €18 per kilo – it's €32.73 per kilo of usable product.
- Formula: True price = Purchase price ÷ (Yield ÷ 100)
- Yield = 100% - Waste percentage
- With 45% trimming loss: €18 ÷ 0.55 = €32.73/kg
Calculating optimal portion size
Start with your target food cost percentage. Most restaurants aim for 28-35%.
💡 Example calculation:
Steak priced at €32.00 (including 9% VAT):
- Price excluding VAT: €32.00 ÷ 1.09 = €29.36
- Target food cost: 30%
- Ingredient budget: €29.36 × 0.30 = €8.81
- Meat at €45/kg: €8.81 ÷ €0.045 = 196 grams
Maximum meat portion: 196 grams
Including garnish and side dishes
Every component on the plate counts. From analyzing actual purchasing data across different restaurant types, the garnishes and sides often represent 15-25% of total plate cost.
💡 Complete dish example:
Full steak plate breakdown:
- Meat 180g: €8.10
- Potatoes 200g: €0.40
- Vegetables 150g: €0.75
- Sauce 50ml: €0.35
- Butter/oil: €0.20
Total plate cost: €9.80
Food cost percentage: €9.80 ÷ €29.36 = 33.4%
Controlling portions in practice
Calculations mean nothing if execution fails. You need systems to ensure consistency.
- Weigh random plates during busy service
- Track ingredient usage against dishes sold
- Train staff on precise portioning techniques
⚠️ Note:
Kitchen scales aren't optional equipment. Guesswork always leads to oversized portions and shrinking margins.
How do you calculate the optimal portion size? (step by step)
Calculate your selling price excl. VAT
Divide your menu price by 1.09 (at 9% VAT). A dish of €32.00 becomes €29.36 excl. VAT. This is your basis for all further calculations.
Determine your desired food cost percentage
Choose a percentage between 28-35% for restaurants. Multiply your selling price excl. VAT by this percentage. At 30%: €29.36 × 0.30 = €8.81 budget.
Calculate cost price per gram of each ingredient
Divide the kilo price by 1000. Meat at €45/kg costs €0.045 per gram. Watch out for trimming loss: at 20% loss, €45/kg actually becomes €56.25/kg.
Distribute your budget across all ingredients
Add up all costs: meat, vegetables, sauce, garnish, oil. Make sure the total stays within your budget. Adjust portions until you're under your desired food cost.
✨ Pro tip
Audit your top 5 dishes over the next 2 weeks by weighing 3 random plates of each during service. These items likely represent 60% of your volume, so getting them right fixes most portion problems.
Calculate this yourself?
In the KitchenNmbrs app you can do this in just a few clicks. 7 days free, no credit card.
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Frequently asked questions
Should I include VAT in my portion calculation?
Never include VAT in food cost calculations. Menu prices show VAT, but your cost analysis should use pre-tax figures only.
How often should I check my portion sizes?
Weigh random plates monthly at minimum. But check immediately after hiring new kitchen staff or receiving supplier price changes.
How do I deal with seasonal fluctuations in purchase prices?
Review portion sizes quarterly and adjust accordingly. You can either reduce portions slightly or modify menu prices to maintain your target margins.
📚 Sources consulted
- EU Verordening 852/2004 — Levensmiddelenhygiëne (2004) — Official source
- EU Verordening 853/2004 — Hygiënevoorschriften voor levensmiddelen van dierlijke oorsprong (2004) — Official source
- EU Verordening 1169/2011 — Voedselinformatie aan consumenten (2011) — Official source
- NVWA — Hygiënecode voor de horeca (2024) — Official source
- NVWA — Allergenen in voedsel (2024) — Official source
- Codex Alimentarius — International Food Standards (2024) — Official source
- FSA — Safer food, better business (HACCP) (2024) — Official source
- BVL — Lebensmittelhygiene (HACCP) (2024) — Official source
- Warenwetbesluit Bereiding en behandeling van levensmiddelen (2024) — Official source
- WHO — Foodborne diseases estimates (2024) — Official source
Food Standards Agency (FSA) — https://www.food.gov.uk
The HACCP standards shown in this application are for informational purposes only. KitchenNmbrs does not guarantee that displayed values are current or complete. Always consult the FSA or your local authority for the latest regulations.
Written by
Jeffrey Smit
Founder & CEO of KitchenNmbrs
Jeffrey Smit built KitchenNmbrs from 8 years of hands-on experience as kitchen manager at 1NUL8 Group in Rotterdam. His mission: give every restaurant owner control over food cost.
Standardize portions, stabilize margins
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