Solder and Flux per Sweat-Joint Takeoff
Solder for a copper rough-in from the joint count: weight per inch = pi/4 x diameter^2 x density; solder = joints x wire per joint x weight per inch. 200 three-quarter-inch joints at about 0.75 in of 1/8 in solid wire each is 0.55 lb (one spool); a 2,000-joint job of 1 in pipe is over 7 lb, eight spools. The wire per joint is a field rule (~the pipe diameter in inches); lead-free solder runs ~0.30 lb/in^3. Flux is a separate small line.
Formula and source
w_per_in = (PI/4) x wire_dia_in^2 x solder_density_lb_in3; solder_lb = joints x wire_in_per_joint x w_per_in; spools = ceil(solder_lb / spool_lb).
Solder-weight identity by name (solid-wire cross-section x density x length); first-principles geometry.
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