Shellfish with shell costs less per kilo, but you're paying for weight you throw away. Many restaurant owners forget to factor in shell loss, which means their actual purchase price ends up 30-60% higher. Here's exactly how to calculate the real cost price per portion.
The difference between shell-on and shell-off prices
With shellfish, you often pay for the total weight, including shell. But you can only use the meat. This is called yield - the usable part after processing.
- Unpeeled shrimp: €12/kg, yield 50-60%
- Peeled shrimp: €22/kg, yield 95%
- Mussels: €4/kg, yield 40-50%
- Whole lobster: €35/kg, yield 25-30%
? Example:
You buy 1 kg of unpeeled shrimp for €12:
- Purchase price: €12/kg
- After peeling: 550 grams usable meat
- Shell loss: 45%
Real price: €12 ÷ 0.55 = €21.82/kg meat
The formula for real purchase price
The basic formula stays the same, regardless of the type of shellfish:
Real price per kg = Purchase price ÷ (Yield % ÷ 100)
Note: you divide by the yield, you don't multiply. If you throw away 40%, you keep 60% - and that becomes more expensive per kilo.
⚠️ Watch out:
Many business owners calculate wrong: €12 × 0.55 = €6.60. This is incorrect! You have less product, so it becomes more expensive, not cheaper.
Yield percentages per shellfish type
These percentages are guidelines. The exact yield depends on quality, season, and your processing skills. Something most kitchen managers discover too late: yield varies dramatically between suppliers, even for the same grade.
- Unpeeled shrimp: 50-60% (head and shell removed)
- Langoustines: 35-45% (lots of shell, little meat)
- Mussels: 40-50% (empty shells, sand)
- Oysters: 15-20% (mostly shell)
- Whole lobster: 25-30% (shell, head, intestines)
- Whole crab: 20-25% (lots of shell)
? Lobster example:
Whole lobster €35/kg, yield 28%:
- Real price: €35 ÷ 0.28 = €125/kg lobster meat
- For 150g portion: €125 × 0.15 = €18.75
Lobster tail ready-to-use costs €95/kg. Then you're better off and save labor.
From real kilo price to portion price
Once you know the real kilo price, calculating the cost per portion is straightforward:
Portion price = Real kilo price × (Portion weight in kg)
For a shrimp salad with 120 grams of peeled shrimp:
- Real price: €21.82/kg
- Portion: 0.12 kg
- Cost: €21.82 × 0.12 = €2.62 per portion
Why ready-to-use can be cheaper
Sometimes it makes sense to buy peeled shellfish, despite the higher kilo price. Also factor in your labor costs. A food cost calculator like KitchenNmbrs helps you compare both scenarios quickly.
? Shrimp example:
Unpeeled vs peeled for 1 kg meat:
- Unpeeled: €12/kg → €21.82/kg meat + 45 min labor
- Peeled: €22/kg directly usable
If your labor costs €20/hour: unpeeled = €21.82 + €15 = €36.82. Then peeled is much cheaper.
Factor in seasonal differences
Shellfish has seasons. Mussels are cheaper in winter and fattier (higher yield). Shrimp are often more expensive in summer due to demand.
Check your purchase prices and yield monthly. What cost €18/kg real price in January can cost €25/kg in July for the same dish.
Related articles
How do you calculate the real purchase price? (step by step)
Measure the yield from your supplier
Buy 1 kg of shellfish and process it the way you normally do. Weigh the usable meat. Divide this by the purchase weight and multiply by 100 for the yield percentage.
Calculate the real kilo price
Divide your purchase price by the yield percentage (as a decimal). At €15/kg and 60% yield: €15 ÷ 0.60 = €25/kg real price.
Work out what one portion costs
Multiply the real kilo price by the weight of your portion in kilograms. For 150 grams: €25 × 0.15 = €3.75 per portion of shellfish.
✨ Pro tip
Test yield percentages every 3 months across different suppliers - 'large' shrimp from one supplier often yield less meat than 'medium' from another. The cheapest per kilo isn't always the most advantageous per portion.
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
Why are unpeeled shrimp cheaper per kilo but more expensive per portion?
How do I know if my supplier's yield is correct?
Should I factor in labor costs for peeling shellfish?
⚠️ 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
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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