Over 60% of restaurants struggle with accurate purchasing, leading to waste or shortages that kill profit margins. Most chefs guess at quantities instead of using the math that tells them exactly what to buy. The formula connecting portion weight to purchase quantity through yield percentage eliminates guesswork completely.
What is yield percentage?
Yield percentage shows how much usable product you'll get after processing your raw ingredients. Fish loses weight from heads, bones, and skin. Meat sheds fat and sinew. Vegetables drop peels and stems.
💡 Example yield percentages:
- Whole salmon to fillet: 55% yield
- Whole beef to portions: 75% yield
- Vegetables (peeled): 85% yield
- Unpeeled shrimp: 50% yield
The basic formula
Here's the math that connects your desired portions to actual purchase amounts:
Purchase quantity = (Desired portion weight × Number of portions) / (Yield percentage / 100)
💡 Example calculation:
You need 50 salmon fillets at 180 grams each:
- Desired portion weight: 180 grams
- Number of portions: 50
- Yield percentage whole salmon: 55%
Calculation: (180 × 50) / (55 / 100) = 9,000 / 0.55 = 16.4 kg whole salmon needed
Why this calculation matters
Guessing quantities creates two expensive problems. Buy too much and you're throwing money in the trash. Buy too little and you can't fulfill orders - the kind of thing you only learn after closing your first month at a loss.
⚠️ Watch out:
Many chefs think: "I need 9 kg of fillet, so I'll order 9 kg of salmon." Wrong! You'll only have 4.95 kg of fillet (9 × 0.55) and you'll be short 4.05 kg.
Determining yield percentage for your own kitchen
Each product yields differently based on quality and how you process it. Test your main ingredients several times using this method:
- Weigh the product when it arrives
- Process it using your normal technique
- Weigh the final usable product
- Calculate: (final weight / initial weight) × 100
💡 Example measuring yield:
2 kg whole salmon purchased, 1.1 kg fillet after filleting:
Yield: (1.1 / 2.0) × 100 = 55%
Impact on your food cost
Yield percentage directly affects your real cost per portion. If you pay €18 per kg but only get 55% yield, your fillet actually costs €32.73 per kg (€18 / 0.55). That's nearly double your purchase price.
Digital tools
Food cost calculators like KitchenNmbrs handle these calculations automatically. You input portion weight and yield percentage, then get exact purchase quantities. This eliminates math errors and speeds up order planning.
How do you calculate the purchase quantity? (step by step)
Determine your yield percentage
Measure the yield percentage for each main ingredient by comparing the initial weight and final weight after processing. Do this a few times to get an average.
Calculate total desired final weight
Multiply your desired portion weight by the number of portions you want to make. For example: 180 grams × 50 portions = 9,000 grams total.
Divide by the yield percentage
Divide the total desired weight by the yield percentage (as a decimal). At 55% yield: 9,000 / 0.55 = 16,364 grams = 16.4 kg purchase quantity.
✨ Pro tip
Test your yield calculations during your slowest 2-week period to build accurate data without pressure. Different knife skills between staff can create 10-15% yield variations on the same ingredient.
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
What if I don't know the yield percentage?
Measure it several times by weighing before and after processing. For standard products, use common percentages: fish 50-60%, meat 70-80%, vegetables 80-90%.
Do I always have to buy exactly this quantity?
No, this is your minimum. Always buy 5-10% extra for safety since yield can vary per delivery and prep accidents happen.
How often should I re-measure yield percentages?
Test your main ingredients 3-4 times to get an average. Re-measure only if you change suppliers or processing methods.
What if my supplier only sells whole kilos?
Always round up. If you need 16.4 kg, order 17 kg. Freeze the extra or use it for daily specials.
Does this formula work for composite dishes?
Yes, but calculate each ingredient separately. A stew needs beef (75% yield), vegetables (85% yield), and spices (100% yield) calculated individually.
How do I handle ingredients with multiple processing steps?
Calculate the combined yield by multiplying each step's percentage. If trimming gives 90% yield and cooking reduces by 20%, your total yield is 72% (0.90 × 0.80).
⚠️ EU Regulation 1169/2011 — Allergen Information — https://eur-lex.europa.eu/eli/reg/2011/1169/oj
The allergen information on this page is based on EU Regulation 1169/2011. Recipes and ingredients may vary by supplier. Always verify current allergen information with your supplier and communicate this correctly to your guests. KitchenNmbrs is not liable for allergic reactions.
In the UK, the FSA enforces allergen regulations under the Food Information Regulations 2014.
📚 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.
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