Trim waste and loss

Gross quantity to buy

How much to buy as purchased so that, after cleaning, there's enough for every portion.

What it is and why it matters

Recipes state clean quantities. To buy, you need the gross quantity: how much to order as purchased so that, after cleaning, there's enough for every portion.

You solve it with the waste factor or with the rule of three, and round the purchase up.

The formula

Clean quantity needed = portions × clean portion
Gross quantity = clean quantity × waste factor
Rule of three: gross quantity = clean quantity × 100 ÷ (100 − trim waste %)

What each value means

Portions: How many guests or portions you'll serve.
Clean portion: How much of the clean ingredient each portion takes, according to the recipe.
Waste factor: Comes from the trim waste % of the raw material.
Gross quantity: What you need to buy, before rounding.

Step by step

Multiply the portions by the clean quantity of each one.
Work out the waste factor of the raw material.
Multiply the clean quantity needed by the factor.
Round up to the unit you buy in.

Worked examples

Grilled salmon for 120 covers

Each portion takes 0.160 kg of clean fillet: 120 × 0.160 = 19.200 kg clean.

Salmon has 25% trim waste, so the factor is 1.333.

Gross quantity = 19.200 kg × 1.333 = 25.600 kg. By the rule of three: if 75% is 19.200 kg, 100% is 19.200 × 100 ÷ 75 = 25.600 kg.

Rounding up, you buy 26 kg.

Study notes

Common mistake
Adding 25% to 19.2 kg gives 24 kg, but trimming that leaves only 18 kg: more than 1 kg short. That is why you use the factor, not a plain percentage.
Rounding
For practicality, round up (25.6 → 26 kg). A little extra is always better than falling short.

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Result

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