Metric Fish Weight Calculator

Estimate the weight of your fish in kilograms by entering the length and girth measurements in centimetres

Measuring Fish Length

Measure the 'short length' of the fish in centimetres, from the tip of the lower jaw to the V of the tail.

Measuring Fish Girth

Measure fish girth in centimetres all the way around the fattest part of the body. It may be easier to measure one side and multiply by two.

How accurate is this fish weight calculator?

This fish weight calculator is based on the fish weight formula: (short length x girth squared) / 800.

This formula tends to work reasonably well for estimating the weight of gamefish like tuna, marlin, swordfish and kingfish, with an accuracy range of around +/- 10%.

Of course, this is just an estimate and can't ever replace a certified scale for an accurate fish weight - as the saying goes: if you don't weight it, you can't say it!

Remember this is a metric fish weight calculator, so you should enter the fish measurements in centimetres (cm) and not inches. Also if you're taking a half-girth measurement from one side of a fish, remember to double it before entering it into the fish weight calculator!

Measuring billfish for a more accurate weight estimate

Because of their variance in shape, size and condition, billfish weight estimates can vary a lot depending on where you take your measurements from. Be absolutely sure you are measuring the short length, which extends from the tip of the bottom jaw to the V of the tail, excluding the bill and tail flukes.

For a more accurate girth measurement, especially on larger and well conditioned fish that are carrying a lot of weight towards the tail end, you may want to take two girth measurements - one from around 15-20cm back from the pectoral fins, and a second one from around 15-20cm in front of the anal fins, then take the average of the two girth measurements (add them together and divide by two).

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