How to Read Reel Line Capacity and Convert It: How Much No. 2 Line Fits on a “3-100” Spool?
Reel spools and boxes list line capacity like “Nylon (No.-m) 2.5-150, 3-100”. Here “No.” is the Japanese line size (gō), and the label means “100 m of No. 3 fits”. But if you actually want to spool No. 2 or No. 1.5, it’s hard to tell how many metres will fit. This article explains how to read line capacity labels, how to convert to a different line size, what to watch for when converting between PE and nylon labels, and how much line each kind of fishing needs.
How to read line capacity labels
The spec sheet of a spinning or baitcasting reel, and the side of the spool, show how much line the reel holds in the form “size-length”. Japanese reels give the size as a line number (gō). Typical labels look like this.
| Example label | Meaning |
|---|---|
| Nylon (No.-m) 2.5-150, 3-100 | Holds 150 m of No. 2.5 nylon or 100 m of No. 3 |
| Fluoro (No.-m) 3-90 | Holds 90 m of No. 3 fluorocarbon |
| PE (No.-m) 0.8-200, 1-150 | Holds 200 m of PE No. 0.8 or 150 m of PE No. 1 |
| Nylon (lb-m) 8-120 | Holds 120 m of 8 lb nylon |
| 3-100 | With no material given, it’s usually the nylon size and length |
When several labels are listed, they all describe the same capacity in different line sizes. “2.5-150, 3-100” gives 2.5 × 150 = 375 and 3 × 100 = 300, which aren’t exactly equal, because manufacturers give approximate figures using commercial line sizes and round lengths. When calculating, use the label closest to the line you want to spool to keep the error small.
How to convert to a different line size
Japanese nylon and fluorocarbon line numbers are set in proportion to the line’s cross-sectional area, so No. 2 line has twice the cross-section of No. 1. The amount of line a spool holds (its volume) is cross-section × length, so for the same material, “line number × length” represents the spool’s capacity.
- 1
Work out the spool’s capacity
Multiply the label’s line number by its length. For 3-100, that’s 3 × 100 = 300.
- 2
Divide by the line number you want to spool
For No. 2, 300 ÷ 2 = 150 m. For No. 1.5, 300 ÷ 1.5 = 200 m.
- 3
Leave a little margin
Filling right up to the spool lip makes line spill off and causes more tangles, so aim to actually spool about 90% of the calculated length.
| Spool label | No. 1.5 | No. 2 | No. 2.5 | No. 3 | No. 4 |
|---|---|---|---|---|---|
| Nylon 2-100 (capacity 200) | About 133 m | 100 m | 80 m | About 67 m | 50 m |
| Nylon 2.5-150 (capacity 375) | 250 m | About 188 m | 150 m | 125 m | About 94 m |
| Nylon 3-100 (capacity 300) | 200 m | 150 m | 120 m | 100 m | 75 m |
| Nylon 3-150 (capacity 450) | 300 m | 225 m | 180 m | 150 m | About 113 m |
| Nylon 4-150 (capacity 600) | 400 m | 300 m | 240 m | 200 m | 150 m |
The relationship between line number and diameter (the number is proportional to the diameter squared) is explained in detail in nylon and fluorocarbon line size, lb and diameter chart.
What to watch for when converting between PE and nylon labels
PE line numbers are based on weight (denier), not thickness. PE is also braided, so its cross-section isn’t round and it packs onto the spool differently from nylon. That means working out PE length from a nylon label with “line number × length” can differ from reality.
- If the spool has a PE label (such as PE (No.-m) 0.8-200), calculate PE from that. Between PE sizes, the line number × length conversion is roughly right.
- If there’s no PE label and only a nylon one, use the line number × length result as a rough guide, then spool a little less and adjust while watching the gap to the lip.
- Fluorocarbon is stiff and bulks up from line memory more than nylon, so when calculating from a nylon label, allow about 10% less to be safe.
How much line each kind of fishing needs
Once you know how much the spool holds, the next question is how many metres are enough. Decide based on casting distance, how far a fish may run, and a spare in case the line breaks off.
| Fishing | Main line length guide | Reasoning |
|---|---|---|
| Sabiki and light casting | Around 100 m | Mostly close in. Spool plenty of cheap nylon and trim it as it wears |
| Light rock fishing for horse mackerel and rockfish, squid jigging (eging) | 100–150 m | Casts of a few dozen metres. 150 m still works after a few break-offs |
| Sea bass and surf fishing | 150–200 m | Long casts, so add a spare for break-offs on top of the casting distance |
| Shore jigging | 200–300 m | Allow for runs by fast pelagic fish and for sinking lures in deep water |
| Surf casting (long distance) | 200 m or more | Casts can exceed 100 m, so leave a big margin |
If the length you want is short for the spool’s capacity, spooling it as is won’t reach the lip and you’ll lose casting distance. In that case, first spool some other line underneath to build up the spool, known as backing. How to work out the length needed is explained in how to calculate backing line length.
Paste a capacity label to convert it
In the Fishing Line Size Converter & Line Capacity Calculator’s “Line capacity conversion”, paste a reel spec sheet or spool label as it is (such as “Nylon (No.-m) 2.5-125, 3-100”, “PE No.1-200m” or “8lb-100m”) and it reads it and calculates how many metres of your chosen line type and size will fit. It also shows a table of length and approximate strength for each line size, so you can compare options like “150 m of No. 2 or 120 m of No. 2.5”.
How PE line sizes relate to strength is summarised in the PE line size and lb chart.
FAQ
- What does a line capacity of “3-100” mean?
- It means 100 m of No. 3 line fits. With no material given, it’s usually the nylon size. For the same material, the spool holds any length that gives the same line number × length, so roughly 150 m of No. 2, 200 m of No. 1.5 or 75 m of No. 4.
- Is it OK to spool a little more than the stated capacity?
- It’s not recommended. If line spills over the spool lip, several coils can come off at once when you cast, causing tangles (wind knots and backlashes). Stop about 1–2 mm below the lip, at around 90% of the calculated amount.
- How much PE fits on a reel that only lists nylon capacity?
- The line number × length conversion gives a rough guide, but because PE numbers are based on weight and its cross-section isn’t round, the real amount will differ. Start with less than the calculated length and adjust while watching the gap to the lip.
- What is a shallow spool?
- A spool with a shallow groove for the line, so it holds less. It suits spooling about 150 m of thin PE and has the advantage of reaching the lip easily without backing. Model names often include codes such as S or SS.
- How do I calculate a line capacity given in lb?
- Convert lb to a line number, then calculate with line number × length. For nylon and fluorocarbon, roughly No. 1 = 4 lb, so 8 lb-120 m is about No. 2 with a capacity of 240. That works out to 80 m of No. 3.
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