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Fishing Line Capacity Calculator

Work out how much line a spool holds from its arbor, lip and width, then how much braid backing to wind first so a set mono topshot finishes just below the lip.

mm
spool hub, line off
mm
outer edge of the spool
mm
line-lay stroke
mm
clearance below the lip
mm
from the line label
%
80–90% is usual

Braid backing + mono topshot

mm
backing line
mm
mono or fluoro
m
1 m ≈ 1.09 yd
Enter the spool and line measurements.

Line is modelled as layers wound on the arbor: each layer adds one line diameter to the radius and holds one spool width of turns at that diameter. Winding density discounts loose, criss-crossed laying. Measure the arbor and lip with calipers and leave a millimetre or two below the lip, because published capacities assume a fuller spool than most reels tolerate. The backing figure is the braid needed to bring the stack up to the point where the chosen topshot ends at the fill line. Results are estimates; everything is calculated in this page and nothing is uploaded or stored.