Largemouth bass length to weight chart
What a largemouth bass weighs at every length from 8 to 26 inches, why girth matters, rough age at length, and how to measure a bass right. A 20 inch bass is about 5.1 lb.
·4 min read·fishline
What does a 20 inch largemouth weigh? About 5.1 lb if it is in average shape. Here is the full chart, how to read it, and why two bass of the same length can weigh a pound or more apart.
| Length | Weight | Rough age |
|---|---|---|
| 8 in | 0.27 lb | 1 to 2 years |
| 10 in | 0.56 lb | about 2 years |
| 12 in | 1.0 lb | 2 to 3 years |
| 14 in | 1.6 lb | about 3 years |
| 16 in | 2.5 lb | about 4 years |
| 18 in | 3.6 lb | about 5 years |
| 20 in | 5.1 lb | 6 to 7 years |
| 22 in | 6.9 lb | about 9 years |
| 24 in | 9.2 lb | 12+ years |
| 26 in | 11.8 lb | 12+ years |
Total length, nose to the tip of the pinched tail. Weights are for a largemouth bass in average shape. A fat fish, like a female before the spawn, weighs more and a thin one less, which a girth measurement picks up. Rows past 24 inches are bigger than typical for the species.
Reading the chart
The weights come from the largemouth formula fishline uses, W = L^3.2 / 2,850, with length in inches and weight in pounds. That curve describes a bass in average shape for its length. A few landmarks worth remembering:
- A 2 pound bass is usually around 15 inches.
- A 3 pounder runs about 17 inches.
- The 5 pound mark lands near 20 inches.
- An 8 pound bass is usually 23 inches or more.
- A 10 pounder needs about 24.5 inches, and plenty of girth.
Notice how fast the weight climbs at the top. Going from 18 to 20 inches adds about 1.5 lb. Going from 22 to 24 adds about 2.2 lb. Every inch on a big bass is worth a lot more than an inch on a small one.
Why the same length can weigh very different
Largemouth vary in shape more than most fish. A female in the weeks before the spawn carries a lot of weight in eggs. A bass in a lake full of shad or bluegill gets deep and thick. A bass that just spawned, or one in a crowded pond with little to eat, can be long and thin. All of them might stretch the tape to the same number.
Girth is how you tell them apart. Wrap a soft tape around the fattest part of the body and use the girth formula: length times girth times girth, divided by 800. A 20 inch bass with a 13 inch girth comes out at 4.2 lb. Give the same fish a 15 inch girth and it is 5.6 lb. With a 16 inch girth, a real football, it is 6.4 lb. The fish weight calculator does this for you and tells you whether your fish is heavier or lighter than average for its length.
How old is that bass?
On fishline's growth curve for largemouth, a 12 inch bass is 2 to 3 years old, a 16 inch bass is about 4 years, and a 20 inch bass is 6 to 7 years. Treat those as a rough middle. Bass in warm southern water with a long growing season reach 20 inches sooner, and bass in northern lakes often take longer. Once a largemouth gets past about 22 inches it grows slowly, so a big fish could be a lot older than its length suggests. The fish age calculator runs the same curve for any length.
Measuring a bass right
Lay the bass flat on a bump board with its mouth closed and its nose against the bump. Pinch the tail lobes together and read total length at the tip. Do not drape a tape over the fish and follow its back, which adds length that is not there. Keep the fish wet, and do it quickly if the bass is going back. Many tournaments and state rules measure largemouth this way, but check the rules where you fish.
Or let the photo do it
If you would rather not wrestle a green fish onto a board, take the photo you were going to take anyway. fishline identifies the bass, finds something in the frame for scale, works out the length and runs this same formula for the weight. Hold the bass side-on, close to your chest, with your hand where the camera can see it. There are more tips on the largemouth bass page and in how to take a fish photo that measures well.