For catch and release fishing events, where you intend to release the bass immediately after catch, the figures in the table below will provide a fairly accurate estimate of the fish’s weight without weighing it. Using this table, you can estimate of a fish’s weight without using a scale and stressing the fish.
The largemouth bass length to weight conversion chart below provides minimum, average, and maximum weight estimates based on the length of a bass in inches and centimeters. For an average size largemouth bass use the “Avg” column. For fleshier bass, use the “Max” column.
| Length | Min Weight | Avg Weight | Max Weight |
|---|---|---|---|
| 10in (25cm) | 6 oz | 8 oz | 9 oz |
| 10.5in (27cm) | 7 oz | 10 oz | 11 oz |
| 11in (28cm) | 8 oz | 11 oz | 12 oz |
| 11.5in (29cm) | 9 oz | 12 oz | 14 oz |
| 12in (31cm) | 11 oz | 14 oz | 1 lb |
| 12.5in (32cm) | 12 oz | 1 lb | 1 lb 1 oz |
| 13in (33cm) | 14 oz | 1 lb 3 oz | 1 lb 5 oz |
| 13.5in (34cm) | 1 lb | 1 lb 5 oz | 1 lb 7 oz |
| 14in (36cm) | 1 lb 2 oz | 1 lb 8 oz | 1 lb 10 oz |
| 14.5in (3cm) | 1 lb 4 oz | 1 lb 10 oz | 1 lb 13 oz |
| 15in (38cm) | 1 lb 6 oz | 2 lb 13 oz | 2 lb 2 oz |
| 15.5in (39cm) | 1 lb 9 oz | 2 lb 1 oz | 2 lb 4 oz |
| 16in (41cm) | 1 lb 11 oz | 2 lb 3 oz | 2 lb 8 oz |
| 16.5in (42cm) | 1 lb 14 oz | 2 lb 8 oz | 2 lb 12 oz |
| 17in (43cm) | 2 lb 1 oz | 2 lb 12 oz | 3 lb |
| 17.5in (44cm) | 2 lb 4 oz | 3 lb | 3 lb 5 oz |
| 18in (46cm) | 2 lb 7 oz | 3 lb 4 oz | 3 lb 10 oz |
| 18.5in (47cm) | 2 lb 11 oz | 3 lb 9 oz | 3 lb 15 oz |
| 19in (49cm) | 2 lb 15 oz | 3 lb 14 oz | 4 lb 5 oz |
| 19.5in (50cm) | 3 lb 3 oz | 4 lb 4 oz | 4 lb 10 oz |
| 20in (51cm) | 3 lb 7 oz | 4 lb 9 oz | 5 lb 1 oz |
| 20.5in (52cm) | 3 lb 12 oz | 4 lb 15 oz | 5 lb 7 oz |
| 21in (53.5cm) | 4 lb | 5 lb 6 oz | 5 lb 14 oz |
| 21.5in (55cm) | 4 lb 5 oz | 5 lb 12 oz | 6 lb 6 oz |
| 22in (56cm) | 4 lb 11 oz | 6 lb 3 oz | 6 lb 14 oz |
| 22.5in (57cm) | 5 lb 1 oz | 6 lb 11 oz | 7 lb 5 oz |
| 23in (59cm) | 5 lb 6 oz | 7 lb 3 oz | 7 lb 14 oz |
| 23.5in (60cm) | 5 lb 12 oz | 7 lb 11 oz | 8 lb 8 oz |
| 24in (61cm) | 6 lb 2 oz | 8 lb 3 oz | 9 lb |
| 24.5in (62cm) | 6 lb 9 oz | 8 lb 12 oz | 9 lb 10 oz |
| 25in (64cm) | 7 lb 6 oz | 9 lb 6 oz | 9 lb 14 oz |
| 25.5in (65cm) | 8 lb 4 oz | 10 lb 2 oz | 10 lb 6 oz |
| 26in (66cm) | 8 lb 11 oz | 10 lb 10 oz | 11 lb 6 oz |
| 27in (69cm) | 9 lb 5 oz | 10 lb 15 oz | 12 lb 9 oz |
| 28in (71cm) | 9 lb 13 oz | 13 lb 7 oz | 14 lb 2 oz |
| 29in (74cm) | 10 lb 5 oz | 14 lb 15 oz | 15 lb 13 oz |
Largemouth bass weight can also be estimated using the following length to weight conversion formulas. These formulas use total length (TL) of the fish, measured from the tip of the snout to the tip of the tail fin when compressed. The most accurate formula for estimating weight incorporates girth. When girth isn’t available, length only formulas can be used to estimate weight.
Find the weight of a largemouth bass using the following length to weight conversion formulas:
- (length x girth x girth)/800 – use for average size bass
- (length x girth x girth)/750 – use for more plumb bass
- (length x length x length)/2700 – use when girth isn’t avaiable
L = Length [in inches] from nose to the fork in the tail
G = Girth [in inches] around the thickest of the body
The 800 is per Outdoor Life and Hal Schramm to calculate average bass weight.
Using length x girth formulas for estimating a fish’s weight are more accurate than formulas based on length alone, as girth accounts for variations in size among fish of the same length. For example, a 24″ bass may weigh between 6 and 9 pounds depending on the region, food supply, time of year and sex.
If girth can’t be obtained, the formula (length x length x length)/2700 will provide a weight estimate for an average size largemouth. If your bass is on the thinner side, increase the divisor (shape factor) from 2700 to 2800. If your bass is on the plump side, decrease the shape factor to 2600.
Measuring Length and Girth of Bass
Having accurate length and girth measurements will improve the accuracy of weight estimations for your bass. For estimating weight, always use the total length (TL) measurement as shown in the diagram below. For largemouth bass, total length is from the tip of the snout to the tip of the tail fin when compressed.
Girth is determined by measuring the circumference at the thickest point of the bass’s midsection.
