The real cost of fish is what you pay divided by the fillet that actually reaches the plate. If you buy whole fish at $14 a kilo and get 420 g of skin-on fillet from every kilo, your fillet costs $33.33 a kilo. If you then throw some of it away at the end of the week because it is past its best, the cost rises again. That freshness loss is the one most kitchens forget.
Two losses: prep and freshness
Prep loss is everything that is not fillet: head, frame, skin, guts, fins, pin bones and any belly you trim off. You measure it once per species and check it again now and then.
Freshness loss is fillet you bought and never served. Fish has few days of shelf life. What you do not sell in time ends up in a cheaper dish or in the bin.
Both use the same idea as the guide to yield percentage:
cost per kg of fillet = price per kg whole ÷ fillet yield
cost per kg served = what you paid ÷ kg of fillet you actually served
How to measure fillet yield
- Weigh the whole fish on your own scale, not just the supplier's.
- Fillet it the way you always do: skin on or off, pin bones out, belly trimmed or not.
- Weigh only the fillet ready to portion.
- Divide fillet by whole weight.
- Repeat with several deliveries of the same species and use the average.
Note the size of the fish too. Yield often changes with size, and a bigger fish may give you more fillet per kilo at the same price. Measure it to find out.
Worked example: fish tacos
You sell fish tacos and can buy either whole fish or ready fillets. These are example numbers; yours will be different.
Option A: whole fish. Four fish weighing 2.00 kg in total at $14.00 per kg: $28.00. You fillet them and get 0.84 kg of skin-on fillet.
- Fillet yield: 0.84 ÷ 2.00 = 42%
- Cost per kg of fillet: 28.00 ÷ 0.84 = $33.33
- Your time: filleting the four takes 12 minutes. At $18.00 an hour, that is $3.60, or 3.60 ÷ 0.84 = $4.29 per kg of fillet
- Total: 33.33 + 4.29 = $37.62 per kg
Option B: ready fillets. Skin-on fillets at $30.00 per kg. You still trim pin bones and thin belly edges and keep 95% of the weight.
- Cost per usable kg: 30.00 ÷ 0.95 = $31.58
The portion. Each order of tacos uses 120 g of fish.
| Option | Arithmetic | Fish cost per order |
|---|---|---|
| Whole fish, your time counted | 0.12 × 37.62 | $4.51 |
| Ready fillets | 0.12 × 31.58 | $3.79 |
| Whole fish at the invoice price (the mistake) | 0.12 × 14.00 | $1.68 |
With these numbers, ready fillets win by 4.51 − 3.79 = $0.72 per order. The whole fish only pays if you use the frames for something you sell, such as a fish stock or soup, or if your supplier's whole price drops.
And the mistake row is the one to watch. Costing the tacos at the whole-fish price per kilo would make the fish look like it costs $1.68 when it costs at least $3.79.
Freshness loss in numbers
Stick with the ready fillets. You buy 5.00 kg for the week at $30.00: $150.00. After trimming at 95% you have 4.75 kg. By Friday, 0.35 kg is past what you are willing to serve and goes in the bin.
- Fillet served: 4.75 − 0.35 = 4.40 kg
- Cost per kg served: 150.00 ÷ 4.40 = $34.09
- Fish per order: 0.12 × 34.09 = $4.09, instead of $3.79
That is $0.30 more per order that appears in no recipe. The guide to measuring and costing food waste shows how to keep track of what you throw away each week.
To bring this loss down: buy more often and in smaller amounts if your supplier allows it, portion and chill as soon as you prep, and have a dish for yesterday's fish (fishcakes, a chowder, a fried fish special). If leftover fish sells in another dish, it is no longer waste.
Heads and frames
Heads and frames are not fillet, but they can be a stock, a soup or a sauce base. If you use them, they have value. The simplest way to count them: put a price on what they save you (the fish or bones you would otherwise buy for stock) and subtract it from what you paid before dividing by the fillet. If they go in the bin, subtract nothing.
Frozen prawns and the ice glaze
Frozen prawns and other frozen seafood often come with a layer of ice. You pay for that ice at the price of prawns. To know what you are really buying, thaw a bag, drain it and weigh it.
Example: a 1 kg bag at $18.00 that weighs 0.80 kg drained.
- Cost per kg of prawns: 18.00 ÷ 0.80 = $22.50
If you then peel or devein them, measure that yield as well and divide again.
The overview of ingredient costs by type compares how fish behaves next to meat, chicken and produce.
Do it with the calculator
The yield calculator gives you the real cost per kg of fillet once you enter the price and the usable weight. Take that cost into the food cost calculator with the tortillas, slaw, sauce and lime to get the full cost of an order.
Frequently asked questions
How much fillet do I get from a kilo of whole fish?
It depends on the species, the size and who is filleting, so weigh it yourself. Different species give very different yields, and the same fish changes from one delivery to the next.
Is it cheaper to buy fillets?
Compare per usable kilo. Divide the whole fish price by your fillet yield and add your filleting time per kilo of fillet. If the ready fillets cost less than that and are just as fresh, buy fillets.
How do I count fish I throw away at the end of the week?
Subtract what you throw away from what you prepped, and divide what you paid by what you actually served. That is your real cost per kilo, with the freshness loss included.
Does frozen seafood have a yield?
Yes: the ice glaze. Thaw and drain a bag, weigh it, and divide the price by the drained weight to find what a kilo of seafood really costs you.