The relationship between portion size and inventory consumption determines how much you order and how much you have left over. Many head chefs estimate this, causing them to order too much or run short. Learn to precisely calculate how much inventory you need per portion.
Why connect portion size and inventory?
Your portion size directly determines how many ingredients you consume per day. If your chef serves 250 grams of steak instead of 200 grams, you're consuming 25% more meat than planned.
? Example:
You expect 50 steak portions of 200g:
- Calculated consumption: 50 × 200g = 10 kg
- Actual portion: 250g
- Actual consumption: 50 × 250g = 12.5 kg
Difference: 2.5 kg = 25% more than expected
The basic formula for inventory consumption
You calculate the relationship between portion and inventory like this:
Inventory consumption = Number of portions × Portion size per ingredient
This seems straightforward, but you need to account for:
- Trim loss (from whole product to portion)
- Cooking loss (what's lost during cooking)
- Variation in portion size by different cooks
- Reserve for busy moments
Step 1: Measure your actual portion size
Many restaurant owners don't know what their chef actually serves. Measure this for a week:
? Practical example:
Weigh 10 random plates of the same dish:
- Plate 1: 220g main ingredient
- Plate 2: 240g main ingredient
- Plate 3: 210g main ingredient
- Average: 225g
You calculated 200g, but serve an average of 225g = 12.5% more
Step 2: Account for trim loss
From whole product to portion, something's always lost. You need to include this in your inventory calculation:
Required purchase = Net portion ÷ (100% - Trim loss%)
? Calculation example:
You want 50 portions of 200g salmon:
- Net needed: 50 × 200g = 10 kg fillet
- Trim loss whole salmon: 45%
- Gross purchase: 10 kg ÷ 0.55 = 18.2 kg whole salmon
So you need to order 18.2 kg to get 10 kg on the plate
⚠️ Note:
Divide by the yield, don't multiply by the loss. With 45% loss you divide by 0.55 (the yield).
Step 3: Plan for variation and busy times
Your inventory needs to be flexible. Plan 10-20% extra for:
- Unexpectedly busy evenings
- Larger portions by different cooks
- Damaged ingredients on delivery
- Tasting and testing in the kitchen
Calculate weekly inventory consumption
For your weekly order use this formula:
Weekly consumption = (Average portions/day × Portion size × 7 days) ÷ Yield × 1.15 (buffer)
? Complete example:
Pasta carbonara, average 25 portions per day:
- Bacon per portion: 40g
- Weekly consumption: 25 × 40g × 7 = 7 kg
- Bacon trim loss: 15%
- Gross purchase: 7 kg ÷ 0.85 = 8.2 kg
- With 15% buffer: 8.2 × 1.15 = 9.4 kg
Order 9.5 kg bacon for this week
Getting these calculations wrong is the kind of thing you only learn after closing your first month at a loss. But the math becomes second nature once you've tracked actual consumption against planned portions for a few weeks.
Digital tracking vs. Excel
You can do these calculations manually, but it takes considerable time. With an app like KitchenNmbrs:
- You set your portion size per dish
- You automatically calculate back to required inventory
- You see immediately what you need to order
- You track what you actually consume vs. what you order
This saves you hours of calculation per week and prevents you from ordering too much or too little.
How do you calculate inventory consumption per portion?
Measure your actual portion size
For a week, weigh the portions of your 5 best-selling dishes. Note the weight of each main ingredient per plate. Calculate the average per dish.
Calculate your trim loss percentage
Measure how much usable product you get from your raw purchase. For example: from 10 kg whole fish to 5.5 kg fillet = 45% trim loss. This varies by product and supplier.
Calculate back to required purchase
Use the formula: (Number of portions × Portion size) ÷ Yield × 1.15 buffer. This gives you the amount you need to order for the number of portions you want to make.
✨ Pro tip
Weigh your top 3 dishes every Tuesday morning for 4 weeks: check 5 random plates per dish. Any portion variance over 15g will cost you €200+ monthly on high-volume items.
Calculate this yourself?
In the KitchenNmbrs app you can do this in just a few clicks. 7 days free, no credit card.
Was this article helpful?
Frequently asked questions
How much buffer should I include in my inventory calculation?
Do I need to account for trim loss if I order pre-portioned?
What if my chef gives different portion sizes?
How often should I check my portion size?
Can I automate this calculation?
What's the biggest portion control mistake restaurants make?
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.
kennisbank.more_in_category
Related questions
Explore more topics
Manage inventory without spreadsheets
Always know what you have in stock and what it's worth. KitchenNmbrs connects inventory to recipes and purchasing for complete oversight. Start your free trial.
Start free trial →