What Does “Pound-Test” Mean on a Fishing Line Label?

Labels Don’t Tell the Whole Story About a Line’s Actual Breaking Strength

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These are typical labels for a nylon monofilament line (left) and a braided microfilament line. Photo © Ken Schultz

Many anglers don’t know exactly what they’re getting when they buy a new line. The packaging promotes the intrinsic strength of the product, which is generally specified as being a certain “pound-test,” but it doesn’t explain exactly what that designation means. Here are important facts about pound-test, otherwise known as strength, as it applies to nylon, fluorocarbon, and microfilament lines, which account for most of the fishing line sold in North America.

“Breaking Strength” and Labels Explained

Breaking strength is the amount of pressure that must be applied to an unknotted line before the line breaks. Every spool of fishing line carries a number that asserts what that product’s breaking strength is.

Spools of fishing line sold in North America are labeled according to breaking strength, primarily via U. S. customary designation as pounds, and secondarily via metric designation as kilograms. For example, a 12-pound-test designation will be followed by a smaller-print designation of 5.4 kilograms, which equals 12 pounds.

Some lines are also labeled by diameter, in inches and millimeters, which can be important. Line diameter is often ignored by North American anglers (except fly anglers because of their use of fine leaders and tippets), but in Europe it is the primary designation of interest. To really compare products, you should know the diameter as well as the actual breaking strength.

Braided lines are also labeled with a nylon monofilament equivalent diameter, stated in pounds. For example, a braided line labeled as 20-pound-test may be labeled as having a .009-inch diameter, and the label will state that this is equivalent to the diameter of a 6-pound-test nylon monofilament line.

The labels for some braids may not specify actual diameter, but may simply state what the nylon mono equivalent is, as in 10-pound-test, 2-pound diameter, like the Power Pro label shown in the accompanying photo.

The reason why labels mention the nylon equivalent is because nylon has for decades been the most widely used fishing line product. Most anglers are familiar with it. The newer microfilaments are less familiar to anglers. Equivalency information helps you relate the diameter of a microfilament fishing line to the diameter of a standard nylon monofilament fishing line.

Wet Breaking Strength Is What Matters

The real issue in breaking strength is not what the label says but what the actual strength of the line on the spool is. Actual strength is determined by how much force it takes to break a line that is wet. This is the standard by which the International Game Fish Association (IGFA) tests every line submitted with record applications. It’s irrelevant how a line breaks in a dry state, since no one fishes a dry line. Most anglers, however, assume that the breaking-strength designation refers to line in its dry state.

Thus, the labeled breaking strength of a fishing line should indicate what happens when it’s wet, not dry.

Unfortunately, this is seldom the case with test lines, and seldom explained in the packaging.

The Difference Between Test and Class Lines

There are two breaking-strength categories. One is referred to as “test,” and the other as “class.” Class lines are guaranteed to break at or under the labeled metric strength in a wet condition, in conformance with metric-based world record specifications established by the IGFA. Such lines are specifically labeled as “class” or “IGFA-class.” The IGFA does not keep records according to U.S. customary measures. Any line not labeled as class line is therefore test line. Perhaps 95 percent of all line sold is categorized as test; some manufacturers use the word “test” on the label, but many do not.

Despite the labeled strength of a test line, there is no guarantee as to the amount of force required to break the line in either a wet or dry condition.

The labeled strength may not reflect the actual force required to break the line in a wet condition (although a few do). Since there are no guarantees with test line, they may break at, under, or over the labeled U.S. customary or metric strength. An overwhelming number break above the labeled strength, some just a little above, some far above.

Certain lines, especially nylon monofilaments, experience slight to significant strength loss when wet. Lesser quality nylon monofilament lines are from 20 to 30 percent weaker when wet than when dry. Thus, if you wrap a dry nylon monofilament line around your hands and pull, it doesn’t mean much.

Braided and fused microfilament lines (called super lines by many) do not absorb water and do not change in strength from dry to wet. Likewise, fluorocarbon lines do not absorb water and do not weaken in a wet state. This doesn’t mean these lines are stronger; it means that what you get when dry is also what you get when wet. It also doesn’t mean that these lines are immune from strength mislabeling, and that a line labeled as 20-pound-test may not actually break at 25 pounds.

This information is essential to people who fish deliberately for world records in specific line categories. The average angler doesn't know most of what is written here, but if you're particular about your fishing - and it is often the little details that make for success - you should.