The simple formula
The truth is that you’ll see conversion charts that will ask for three measurements of the fish itself. Here in the US, the formula will differ from our neighbors over in Canada. Must be all those Tim Horton’s donuts- eh? So let’s cut to the chase already. According to the IGFA (The International Game Fish Organization), the formula is simple.
Start with the length of the fish from nose tip to the fork of the tail fin. Then use a string to measure the girth at the fattest point. This is at the top of the dorsal fin and under the pectoral fins. Mark the string and measure that girth. Then take your smartphone and get into the calculator.
Add the length of the Bass x the girth and again x the girth, finally dividing by 800. This will give you the rough estimate that will give you that number in pounds. It’s easy to remember:
Length x Girth x Girth / 800
Now, this applies to bigmouth bass according to the Southeast region, so the 800 number is sometimes flexible according to region and species. In general, this number applies to all average bass fish weight. It’ll never be as accurate as World Record fishing formulas, but close enough to tell your fishing buddies.
Is there a weight difference between Bass species?
You bet there is and there are a lot of good reasons why. There are dozens of bass species all over the US and they’ve all grown in different water conditions. You will find that certain seasons and breeds will all have variants in weight fluctuations. This is where the girth factor helps determine the proper fish weight. Over in Canada as mentioned before, they have their conversion weight chart that is nearly identical to the IGFA weight conversion formula. How much does a bass weigh, it looks like this:
Bigmouth bass: Length x Girth x Girth / 1050
Smallmouth bass: Length x Girth x Girth / 1100
You can easily see that their divided number is higher based on the species and weight fluctuations. So for an all-round dividing number, you can float between 800-1100 and compare which formula works best for your region you fish from.
Easy conversion chart
As an average spot-on reference and you have no calculator to work with, here are measurements that will give you a ball park estimate that is pretty darn close. Always keep in mind that 12 inches equal one foot. In this case, one pound per 12 inch bass. It works its way upward to 20 inches which can be divided by 4. This can be converted into 4 pounds.
- 12” – 1.0 lb
- 13” – 1.25 lb
- 14” – 1.75 lb
- 15” – 2.0 lb
- 16” – 2.25 lb
- 17” – 2.5 lb
- 18” – 3.5 lb
- 19” – 3.75 lb
- 20” – 4.0 lb
Why is there a need to weigh your bass?
Depending on where you fish, there are rules- duh! Yes, kids, it’s true that you need to have permission or a valid permit in most cases to fish. That’s why it’s a regulated sport. But it also helps you determine what you can keep and what you need to throw back in. In some states, it can begin at 12 inches and you are limited to only two per day.
Depending on where you live you’ll need to check your local state regulations for weight and length limits. If you don’t have a smartphone, (and seriously who doesn’t these days), you can memorize these simple conversion charts! This way you won’t be stuck in dead water trying to figure out what you can keep and what you can’t. So does that tell you how much does a bass weigh? Now you know!