Prawns are sold in a code that nobody explains. A box says 16/20 and another says 6/8, one is priced per kilo net and the other per kilo gross, one arrives as a solid block and the other as loose pieces. Chefs end up buying on price and discovering the difference on the pass. This guide sets out what the codes mean and what actually changes on the plate.
Size codes and why two systems exist
A prawn size code is a count, not a measurement. It tells you how many pieces make up a fixed weight, so a smaller number means a bigger prawn. The trap is that the fixed weight is not the same everywhere.
The American and European trade counts by the pound. A box marked 16/20 contains between sixteen and twenty prawns per pound. Much of the Asian trade, particularly for head-on product, counts by the kilogram instead, so a box marked 6/8 contains six to eight prawns per kilo, which are very large prawns indeed. Both conventions are correct, and reading one as the other will put you badly wrong on portioning.
Reference table for the common grades
| Count per pound | Pieces per kg | Average piece | Typical use |
|---|---|---|---|
U/10 | Under 22 | 45g and up | Grilled centrepiece, butterfly, tempura showpiece |
13/15 | 29 to 33 | 30 to 35g | Skewers, main course prawns, premium starters |
16/20 | 35 to 44 | 23 to 28g | The workhorse grade for curries, stir fry and butterfly |
21/25 | 46 to 55 | 18 to 22g | Volume curries, pakora, mixed seafood dishes |
26/30 | 57 to 66 | 15 to 17g | Fried rice, noodles, sushi and salads |
31/40 | 68 to 88 | 11 to 15g | Cost-controlled mixes, soups, roll fillings |
41/50 | 90 to 110 | 9 to 11g | Sauces, dumpling fillings, garnish |
To convert a per-pound count yourself, multiply by 2.2 for pieces per kilo. To get the average piece weight, divide 454 by the count. A 21/25 grade therefore runs at roughly 46 to 55 pieces per kilo and about twenty grams a prawn.
IQF against block frozen
This is the decision that changes your kitchen workflow more than any other.
IQF, individually quick frozen
Each prawn is frozen separately, so you take out exactly what you need and the rest stays frozen. Higher price per kilo, far less waste, and no thawing a whole slab for six prawns.
Block frozen
Frozen as a solid slab in a carton. Cheaper per kilo and excellent protection against freezer burn, but you commit to defrosting the whole block once you start it.
The rule of thumb: if prawns come off your menu in unpredictable quantities, IQF pays for itself in waste avoided. If you are producing in batches to a known volume, block frozen is the better economics. Plenty of kitchens run both, with a block for prep and an IQF bag for a la carte.
Think GG stocks both, plus shell-on grades, across the IQF king prawn, block king prawn and shell-on king prawn ranges, alongside large freshwater prawns.
The presentation codes
| Code | Means | When it makes sense |
|---|---|---|
HOSO | Head on, shell on | Grilling whole, display counters, dishes where the head carries flavour |
HLSO | Headless, shell on | Shell-on service, better yield than HOSO, cheaper than peeled |
PD | Peeled and deveined | Straight into the pan, zero prep labour |
PUD | Peeled, undeveined | Smaller grades where the vein is not visible on the plate |
PDTO | Peeled and deveined, tail on | Tempura, butterfly, anything held by the tail |
EZP | Easy peel, shell scored | Shell-on presentation without the customer fighting it |
Yield changes everything. A kilo of HOSO does not give you a kilo of edible prawn. Heads and shells are a substantial share of the weight, so a cheaper price per kilo on head-on product can work out dearer per portion than peeled. Compare on cost per finished portion, not cost per case.
Glaze, and the weight you are really buying
Frozen prawns are coated in a thin layer of ice called glaze, which protects them from freezer burn and dehydration. Glaze is legitimate and necessary. It is also weight you cannot eat, and the percentage varies considerably between suppliers.
Look for net weight rather than gross weight on the specification. A box described as ten by one kilo may hold ten kilos gross with a stated net figure underneath, and the gap between the two is the glaze. When you compare two quotes, convert both to a price per kilo of net product before deciding which is cheaper. Two boxes at the same headline price can differ meaningfully once the ice is accounted for.
Species you will meet
Black tiger
Bold striping, firm texture, holds shape well under heat. The classic choice for grilling and for dishes where the prawn is the star.
Vannamei
Whiteleg prawn. Milder, sweeter, consistently graded and generally better value at volume. The default for most kitchens.
Freshwater prawns
Large river prawns with long claws and a distinctive sweet flavour, sold in big grades for centrepiece dishes.
Buying well from Think GG
Order one grade above what you think you need and cost it properly before committing. Most kitchens underestimate how much a plate improves by moving from 26/30 to 21/25, and how little that costs per portion.
Ask Think GG for the specification sheet before your first order: species, count, presentation, net weight and origin. We will send it. If you are working out the rest of the seafood board at the same time, our guide to baby octopus, blue swimming crab and squid covers the exotic side, and the fish fillet range covers the rest.
On certification. Think GG’s two fully halal-certified ranges are the Omakase by Cupid frozen range and the halal sauce range, both imported directly from the certified manufacturers. Prawns and seafood sit in a different category, where Think GG sources halal wherever possible and will send you the specification on any line so you can check it yourself.
Common questions
What does 16/20 mean on a box of prawns?
Sixteen to twenty prawns per pound, which works out at roughly thirty five to forty four pieces per kilo, or about twenty three to twenty eight grams per prawn. A lower count number means a larger prawn.
Is IQF better than block frozen?
Neither is better in absolute terms. IQF lets you use exactly what you need and cuts waste, which suits unpredictable service. Block frozen is cheaper per kilo and better suited to batch production where the whole block gets used.
What is glaze on frozen prawns?
A protective coating of ice applied during freezing to prevent dehydration and freezer burn. It is necessary, but it counts towards gross weight, so always compare suppliers on net weight.
Are prawns halal?
Shafi’i, Maliki and Hanbali scholars permit prawns as game of the sea. The Hanafi position treats them with more caution. Processing is a separate matter, so check for alcohol-based marinades on any value-added or breaded product.
What is the difference between black tiger and vannamei?
Black tiger prawns are firmer with a more pronounced flavour and bold striping, suited to grilling. Vannamei are milder and sweeter, more consistently graded and usually better value at volume.
Does Think GG supply prawns to takeaways and fish and chip shops?
Yes. Think GG supplies block, IQF and shell-on king prawns across the full grade range, plus freshwater prawns, to trade customers nationwide. Send your grade and volume through the Think GG contact page for a quote.
Get a prawn quote from Think GG
Tell us the grade, presentation and monthly volume and we will price it against your postcode.
See the prawn range Contact Think GG
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