🧵 Line Diameter to Pound Test Reference Chart

A quick reference for approximate line diameter versus pound test. Braided line packs much more strength into a thinner diameter than monofilament or fluorocarbon.

Reading the chart

LINE_TABLE is a fixed seven-row lookup from 4 lb to 50 lb test, each row carrying two diameters: one for monofilament and fluorocarbon, one for braid. Nothing is calculated and nothing to enter.

The gap between the two columns is remarkably steady. At 10 lb the chart gives 0.011 in against 0.006 in; at 20 lb, 0.016 against 0.009; at 50 lb, 0.028 against 0.015. Braid lands near 55% of the mono diameter throughout, which means about a third of the cross-sectional area, since area follows the square.

What the numbers are worth in practice

Spool capacity follows diameter, not rating. Swapping 20 lb mono for 20 lb braid takes you from 0.016 to 0.009 in, and (0.016 ÷ 0.009)² is 3.2, so roughly three times the yardage fits.
Convert if your line is labelled in millimetres. Multiply inches by 25.4: 0.011 in is 0.28 mm, and 0.016 in is 0.41 mm.
Compare brands on diameter. Two spools both marked 15 lb can differ by several thousandths, and the thinner one casts further and sinks faster whatever the label claims.

Pound test is not a regulated measurement. Most mono breaks somewhere above its rating, braid ratings are often conservative by a wide margin, and line sold to IGFA class rules is deliberately built to break under it. Braid diameters are the softest figures of all, because a woven line is not round and flattens under tension.

Frequently asked questions

What diameter is 20 lb braid?

About 0.009 in, or 0.23 mm, on this chart. Real spools vary with carrier count and coating, so a four-carrier and an eight-carrier 20 lb braid measure differently — check the label before working out reel capacity.

Why is braid so much thinner than mono at the same pound test?

The fibres carry far more load per unit of area, and there is no stretch to engineer in. That is where the 55% figure comes from: same stated strength, roughly a third of the cross-section.

Is 30 lb braid the same as 30 lb mono?

Only in the number printed on the box. At 0.011 against 0.020 in the braid casts further and cuts through weed and current, but it has no stretch to cushion a lunging fish, so drag settings and knots that were fine on mono need rethinking.