Fishing Line 호 (Gou) to Diameter Chart

Understanding the fishing line size chart — concept and principle

In Korea and Japan, monofilament fishing line is sold by number, written 호 in Korean and 号 (gō) in Japanese, rather than by pound test. This chart converts a line number into its standard diameter in millimetres for nylon and fluorocarbon monofilament, so you can compare spools from different brands, match line to a reel's capacity chart, or translate a Korean rig recipe into metric or Western specifications.

How it is calculated

The calculator looks the number up in the standard diameter table rather than computing it. Selected values:

• 0.4호 = 0.104 mm, 0.6호 = 0.128 mm, 0.8호 = 0.148 mm
• 1호 = 0.165 mm, 1.5호 = 0.205 mm, 2호 = 0.235 mm, 2.5호 = 0.260 mm
• 3호 = 0.285 mm, 4호 = 0.330 mm, 5호 = 0.370 mm, 6호 = 0.405 mm
• 8호 = 0.470 mm, 10호 = 0.520 mm

The principle

The line number tracks the line's cross-sectional area, which is what determines how much material, and roughly how much strength, a monofilament has. Area grows with the square of the diameter, so the diameter grows with the square root of the number: diameter ≈ 0.165 mm × √(호). This rule reproduces the table within a few thousandths of a millimetre; for example, 0.165 × √4 = 0.330 mm for 4호, and 0.165 × √10 ≈ 0.522 mm for 10호. Doubling the number therefore does not double the thickness: 2호 is only about 1.4 times as thick as 1호, but has about twice the cross-section.

Worked example

Default input: 2호.

1. Find 2 in the table: the standard nylon diameter is 0.235 mm.
2. Check with the square-root rule: 0.165 × √2 ≈ 0.233 mm, within 0.002 mm of the table value.

The calculator shows 0.235 mm for 2호, matching the table.

How to read the result

Thinner line casts farther, sinks faster, is less visible and lets a reel hold more, but it has less breaking strength and abrasion resistance. Light freshwater and small saltwater fish often use about 1–3호, while rock fishing for larger fish or heavy leaders use higher numbers. The actual breaking strength depends on the material and brand; check the pound or kilogram value printed on the spool.

Common mistakes

• Applying this table to braided PE line. PE line also uses 호 numbers, but on its own scale, with very different strength for the same number.
• Assuming a fixed pound test per 호. Strength varies between nylon, fluorocarbon and brands.
• Treating a doubled 호 number as doubled diameter.
• Ignoring that real diameters may differ slightly from nominal values.

Frequently asked questions

What is the diameter of 3호 line?

0.285 mm.

How strong is 2호 line?

Often around 8–9 lb for nylon, but it varies by brand and material; check the spool.

Is 1호 the same for nylon and fluorocarbon?

Yes, the standard diameter is the same (0.165 mm), but strength and density differ.

Sources: Japan Fishing Tackle Manufacturers Association (JAFTMA), standard diameters for fishing line numbers (号)