What is the difference between product weight and round weight?
Product weight (produktvekt) is the actual weight of fish in the condition it is landed — whole, gutted, headed or filleted. Round weight (rundvekt) is the back-calculated live weight of the whole fish, derived by multiplying product weight by an official conversion factor. Landings statistics use product weight; quotas are managed in round weight.
When a vessel lands its catch, the fish is rarely whole — it may be gutted at sea, headed, filleted or otherwise processed. Product weight is what is actually weighed at landing for that product condition. To compare or sum catch across conditions and back to the live fish, an official conversion factor is applied: round weight equals product weight times that factor. So round weight is derived, not measured.
Conversion factors vary by species and product. For cod, gutted with head is about 1.18, gutted without head (headed-and-gutted) about 1.50, salted and dried products higher still; haddock and saithe have their own factors. Byproducts such as roe, liver and heads carry a factor near zero, which is why a notable share of landing records show a round weight of zero while product weight is populated — the round-weight conversion simply suppresses these byproducts.
The practical consequence is that the two measures answer different questions. Product weight best reflects what was actually landed and traded, and it matches the figures industry participants reconcile against, so it is the right basis for landings volume statistics. Round weight, being the live-weight basis on which quotas are set and settled, is the right measure for quota and stock-utilisation analysis. Mixing the two — for example comparing product-weight landings against round-weight quotas — produces misleading results.
Frequently asked questions
- Which weight should I use for landings volumes?
- Product weight. It reflects what was actually landed in its product condition and matches the figures the industry reconciles against. Round weight runs higher and has more zero-value records.
- How is round weight calculated?
- Round weight equals product weight multiplied by an official conversion factor that depends on the species and product condition. It is a derived live-weight estimate, not a direct measurement.
- Why do some records show zero round weight?
- Byproducts such as roe, liver and heads are assigned a conversion factor near zero, so their round weight comes out as zero even though their product weight is recorded.
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