Fish Weight Calculator
Estimate the weight of your catch using the standard fisheries length-girth formula used by state fish and wildlife agencies. Supports 20+ species.
Enter Measurements
Tip of mouth to end of tail (fully extended)
Circumference at the widest point
Enter length and girth to calculate weight
Largemouth Bass — Species Info
(Micropterus salmoides)
22.4 lbs
L × G² ÷ 800
L³ ÷ 1200
Lakes, reservoirs, ponds, slow rivers
Measuring Tips
- Measure total length from tip of mouth to end of tail (compressed)
- Girth is measured at the widest point behind the pectoral fins
- Early morning and evening are peak feeding times
| Length | Est. Weight (No Girth) | Girth 50% of Length | Girth 58% of Length | Girth 65% of Length |
|---|---|---|---|---|
| 6" (15 cm) | 3 oz | 1 oz | 1 oz | 2 oz |
| 8" (20 cm) | 7 oz | 3 oz | 3 oz | 4 oz |
| 10" (25 cm) | 13 oz | 5 oz | 7 oz | 8 oz |
| 12" (30 cm) | 1 lb 7 oz | 9 oz | 12 oz | 15 oz |
| 14" (36 cm) | 2 lbs 5 oz | 14 oz | 1 lb 2 oz | 1 lb 7 oz |
| 16" (41 cm) | 3 lbs 7 oz | 1 lb 4 oz | 1 lb 12 oz | 2 lbs 3 oz |
| 18" (46 cm) | 4 lbs 14 oz | 1 lb 13 oz | 2 lbs 7 oz | 3 lbs 1 oz |
| 20" (51 cm) | 6 lbs 11 oz | 2 lbs 8 oz | 3 lbs 6 oz | 4 lbs 4 oz |
| 22" (56 cm) | 8 lbs 14 oz | 3 lbs 5 oz | 4 lbs 8 oz | 5 lbs 10 oz |
| 24" (61 cm) | 11 lbs 8 oz | 4 lbs 5 oz | 5 lbs 13 oz | 7 lbs 5 oz |
| 26" (66 cm) | 14 lbs 10 oz | 5 lbs 8 oz | 7 lbs 6 oz | 9 lbs 5 oz |
| 28" (71 cm) | 18 lbs 5 oz | 6 lbs 14 oz | 9 lbs 4 oz | 11 lbs 9 oz |
| 30" (76 cm) | 22 lbs 8 oz | 8 lbs 7 oz | 11 lbs 6 oz | 14 lbs 4 oz |
| Species | With Girth Divisor | No Girth Divisor | World Record |
|---|---|---|---|
Largemouth Bass Micropterus salmoides | ÷ 800 | ÷ 1200 | 22.4 lbs |
Smallmouth Bass Micropterus dolomieu | ÷ 800 | ÷ 1350 | 11.94 lbs |
Striped Bass Morone saxatilis | ÷ 800 | ÷ 900 | 81.88 lbs |
Rainbow Trout Oncorhynchus mykiss | ÷ 800 | ÷ 900 | 48 lbs |
Brown Trout Salmo trutta | ÷ 800 | ÷ 900 | 44.51 lbs |
Brook Trout Salvelinus fontinalis | ÷ 800 | ÷ 900 | 14.5 lbs |
Lake Trout Salvelinus namaycush | ÷ 800 | ÷ 800 | 102 lbs |
Walleye Sander vitreus | ÷ 900 | ÷ 2700 | 25 lbs |
Northern Pike Esox lucius | ÷ 800 | ÷ 3500 | 55.1 lbs |
Muskellunge (Muskie) Esox masquinongy | ÷ 800 | ÷ 3500 | 67.5 lbs |
Channel Catfish Ictalurus punctatus | ÷ 900 | ÷ 1300 | 58 lbs |
Flathead Catfish Pylodictis olivaris | ÷ 800 | ÷ 1200 | 123 lbs |
Blue Catfish Ictalurus furcatus | ÷ 900 | ÷ 1300 | 143 lbs |
Bluegill Lepomis macrochirus | ÷ 1200 | ÷ 1200 | 4.75 lbs |
Black Crappie Pomoxis nigromaculatus | ÷ 1400 | ÷ 1400 | 6 lbs |
White Crappie Pomoxis annularis | ÷ 1400 | ÷ 1400 | 5.375 lbs |
Chinook (King) Salmon Oncorhynchus tshawytscha | ÷ 800 | ÷ 800 | 97.25 lbs |
Coho (Silver) Salmon Oncorhynchus kisutch | ÷ 800 | ÷ 900 | 33.5 lbs |
Atlantic Salmon Salmo salar | ÷ 800 | ÷ 900 | 79 lbs |
Common Carp Cyprinus carpio | ÷ 750 | ÷ 700 | 105 lbs |
Redfish (Red Drum) Sciaenops ocellatus | ÷ 900 | ÷ 1000 | 94.2 lbs |
How Fish Weight Calculators Work
The Standard Formula
The most accurate field method uses two measurements: total length and girth. The formula is: Weight (lbs) = (Length × Girth²) ÷ Divisor, where all measurements are in inches. The divisor varies by species to account for differences in body shape and density.
Why Does the Divisor Vary by Species?
Each species has a unique body shape. Deep-bodied fish like bluegill and carp have more mass per inch than elongated fish like pike or walleye. The divisor is calibrated from measurements of thousands of fish weighed at boat ramps and by fisheries biologists across the country.
How Accurate Is This Calculator?
With accurate girth and length measurements, this formula is typically accurate within ±5–10% for most fish in average body condition. Fish that are exceptionally fat (pre-spawn, well-fed) will weigh more than the estimate; thin or post-spawn fish will weigh less. The length-only formula (no girth) has higher variance.
How to Measure a Fish
- Place the fish on a flat measuring board or ruler.
- Measure total length from the tip of the closed mouth to the farthest tip of the tail (with tail lobes compressed for bass; fork length for some species).
- Measure girth at the widest point of the body, typically just behind the pectoral fins.
- Enter both measurements above for the most accurate weight estimate.