Fish Weight Calculator
Estimate the weight of 14 common New Zealand fish species from a single measurement — fork length for inshore species, or length and girth for billfish and sharks.
Weight estimates use length-weight constants published by NIWA and FishBase for New Zealand fish populations. Results are accurate to within 10–15% for a healthy fish. For billfish, the girth-based formula follows the IGFA / MBGLAC standard used by NZ big game clubs. Learn about the methodology →
cm
cm
Lower jaw to tail fork
cm
Legal size
Undersize — release this fish
No minimum size set
Bag limit: per day
Formula source:
— verified .
Legal sizes and bag limits reflect NZ MPI rules —
always verify at mpi.govt.nz.
NZ Legal Size & Bag Limit Reference
Minimum legal sizes and daily bag limits for recreational fishing in New Zealand. Rules may vary by region — always confirm at mpi.govt.nz before retaining fish.
| Species | Min. Length | Daily Bag Limit | Notes |
|---|---|---|---|
|
Barracouta
Thyrsites atun
|
— | 30 / day | No minimum size, 30/day. Primarily a South Island species. |
|
Black Marlin
Makaira indica
|
— | 1 / day | Tag and release strongly encouraged |
|
Blue Cod
Parapercis colias
|
30 cm | 10 / day | 30 cm min; check area-specific SI rules |
|
Blue Marlin
Makaira nigricans
|
— | 1 / day | Tag and release strongly encouraged |
|
Blue Moki
Latridopsis ciliaris
|
40 cm | 15 / day | 40cm all areas. 15/day South Island; 20/day North Island. |
|
Bluenose
Hyperoglyphe antarctica
|
— | 5 / day | |
|
Butterfish
Odax pullus
|
35 cm | 15 / day | 35cm all areas. 15/day South Island; 20/day North Island. |
|
Eel
Anguilla spp.
|
— | 6 / day | No minimum size, 6/day all areas (freshwater and saltwater). |
|
Elephant Fish
Callorhinchus milii
|
— | 5 / day | 5/day South Island; 20/day North Island. |
|
Flatfish
Rhombosolea spp.
|
25 cm | 20 / day | General flatfish (excl. sand flounder). 25cm all areas. |
|
Grey Mullet
Mugil cephalus
|
— | 20 / day | |
|
Hapuka
Polyprion oxygeneios
|
— | 5 / day | Combined Groper/Hapuku/Bass daily bag limit of 5 (no more than 3 kingfish in that 5). |
|
John Dory
Zeus faber
|
25 cm | 10 / day | |
|
Kahawai
Arripis trutta
|
— | 15 / day | No minimum size. 15/day South Island areas; 20/day North Island. |
|
Kingfish
Seriola lalandi
|
75 cm | 3 / day | 75cm NI / 65cm SI — check your area |
|
Red Cod
Pseudophycis bachus
|
25 cm | 10 / day | 25cm all areas. 10/day South Island; 20/day North Island. |
|
Red Gurnard
Chelidonichthys kumu
|
25 cm | 20 / day | |
|
Red Moki
Cheilodactylus spectabilis
|
40 cm | 15 / day | 40cm all areas. 15/day South Island; 20/day North Island. |
|
Rig
Mustelus lenticulatus
|
— | 5 / day | No minimum size. 5/day South Island; 20/day North Island. |
|
Sand Flounder
Rhombosolea plebeia
|
23 cm | 20 / day | |
|
School Shark
Galeorhinus galeus
|
— | 5 / day | No minimum size. 5/day South Island; 20/day North Island. |
|
Snapper
Pagrus auratus
|
30 cm | 7 / day | 30cm min (SNA1 east coast); 27cm west coast. 7/day SNA1; 3/day Marlborough Sounds. Always check MPI for your area. |
|
Striped Marlin
Kajikia audax
|
— | 1 / day | Tag and release strongly encouraged |
|
Tarakihi
Nemadactylus macropterus
|
25 cm | 20 / day | |
|
Trevally
Pseudocaranx georgianus
|
25 cm | 20 / day | |
|
Trumpeter
Latris lineata
|
35 cm | 15 / day | 35cm, 15/day. Primarily a South Island species. |
|
Warehou
Seriolella brama
|
— | 15 / day | No minimum size, 15/day. Primarily a South Island species. |
|
Yellowfin Tuna
Thunnus albacares
|
— | 15 / day | Pelagic species — confirm current WCPFC/MPI rules |
Legal size data sourced from NZ MPI Fisheries regulations 2024. This table is a guide only — verify current rules at mpi.govt.nz.
Frequently Asked Questions
Measure the fork length — from the tip of the snout to the fork in the tail —
in centimetres. Select Snapper in the calculator and enter the length.
The result uses the formula W = 0.0107 × L3.13, a
NIWA-derived constant for the New Zealand snapper population.
A 40 cm snapper weighs approximately 0.8 kg; a 60 cm snapper approximately 2.7 kg.
The calculator covers 14 New Zealand species: Snapper, Kingfish, Kahawai,
Trevally, Hapuka, Bluenose, Blue Cod, John Dory, Tarakihi, Yellowfin Tuna
(length-weight formula) and Striped Marlin, Black Marlin, Blue Marlin,
Mako Shark (girth-based billfish formula).
Estimates are accurate to within 10–15% for a healthy fish in average condition.
Fish in spawning condition, unusually fat or lean may fall outside this range.
The estimate reflects an average fish of that length for the New Zealand population.
For competition purposes, always use certified scales — this calculator is a guide only.
The minimum legal size for snapper is 30 cm (fork length) in most
New Zealand areas, with a daily bag limit of 10 fish. Some areas have additional
restrictions — always confirm current rules at
mpi.govt.nz.
Kingfish minimum legal size is 75 cm in the North Island and
65 cm in the South Island, with a daily bag limit of 3 fish.
Always verify at mpi.govt.nz for your exact area.
Measure fork length — from the tip of the snout to the fork in
the tail, with the fish lying flat. For billfish and sharks, also measure
girth at the widest point of the body (usually behind the
pectoral fins). All measurements in centimetres.
For inshore species: W = a × Lb, where L is fork length in cm
and W is weight in kg. The constants a and b come from FishBase and NIWA research
for New Zealand populations.
For billfish and sharks: W = G² × L ÷ divisor, where G is girth in cm —
consistent with the IGFA / MBGLAC standard used by NZ big game fishing clubs.
Full methodology →