Smallmouth fight well above their weight — but how much do they actually weigh? Use this smallmouth bass length-to-weight chart to estimate your catch from its length, whether you’re culling in a tournament or just curious about that river bronzeback.
Smallmouth Bass length-to-weight chart
| Length | Average weight |
|---|---|
| 10″ | 0.63 lb |
| 11″ | 0.83 lb |
| 12″ | 1.08 lb |
| 13″ | 1.37 lb |
| 14″ | 1.72 lb |
| 15″ | 2.11 lb |
| 16″ | 2.56 lb |
| 17″ | 3.07 lb |
| 18″ | 3.65 lb |
| 19″ | 4.29 lb |
| 20″ | 5 lb |
| 21″ | 5.79 lb |
| 22″ | 6.66 lb |
These values use the standard smallmouth formula, weight (lb) = length³ ÷ 1,600 (length in inches), which closely tracks published In-Fisherman data for a fish in average condition.
What’s an average smallmouth — and what’s a trophy?
Most keeper smallmouth run 12–16 inches and about 1–2 pounds, with a 3–4 lb fish being a “good one” in most waters. Anglers widely treat 20 inches or 5 pounds as trophy class; on premier fisheries like the Great Lakes and St. Lawrence, the bar rises to 6 lb+. (These are angler conventions, not official standards.) The IGFA all-tackle record is 11 lb 15 oz, caught at Dale Hollow Lake on the Tennessee–Kentucky line in 1955 — a record briefly disqualified in the 1990s and then formally reinstated in 2005.
Put a number on your exact fish (worked example)
Length-only charts can’t tell a lean river fish from a chunky lake bronzeback. Girth can:
Weight (lb) = Length × Girth² ÷ 800
An 18-inch smallmouth with a 13-inch girth works out to 18 × 13 × 13 ÷ 800 = 3.8 lb, a touch above the 3.65 lb the length-only chart predicts — a well-fed fish. Measure both and let the free fish weight calculator do it (usually within 5–10%); see how to estimate a fish’s weight if you’re new to it.
Why two smallmouth of the same length weigh differently
Pre-spawn females in late spring carry eggs and hit their peak weight. Forage matters too — smallmouth gorged on crayfish and baitfish run heavier than lean current-fighting river fish. Body depth and region round it out, which is why the chart is a starting point.
Where and when to find bigger smallmouth
Smallmouth love cool, clear, oxygen-rich water with rock — boulder-strewn lake shorelines, reservoir points, and gravel runs and pools in rivers, most active around 68–72°F. Because crayfish are a signature forage, crayfish-imitating tubes, jigs, and soft plastics worked on rocky bottoms are money. The trophy window is pre-spawn/early spawn.
Smallmouth bass weight FAQ
How much does a 20-inch smallmouth weigh? About 5 pounds in average condition — a genuine trophy in most waters.
What’s a trophy smallmouth bass? Generally 20 inches or 5 lb; 6 lb+ on top-tier fisheries.
Why do smallmouth feel heavier than they weigh? They’re famously strong fighters that use current and aerial jumps — a 3-pounder fights like a bigger fish.
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