Weld Filler Metal Weight Calculator

Ordering the right amount of filler metal before a job, and not running out mid-pass, means knowing the weld cross-section area, the total weld length, and the deposition efficiency of the process.

The cross-sectional area depends on the joint type:

For a butt weld (V-groove, 60° included angle): cross_section = thickness² × tan(30°) = thickness² × 0.577

For a fillet weld, this page sizes the leg at 0.7 × plate thickness, which is the usual structural minimum for a full-strength joint: cross_section = 0.5 × leg_size²

Shop practice often sets the leg equal to the thinner plate instead, which is a heavier weld. If your drawing calls a leg size, take it from there and enter it directly on the welding rod calculator, which asks for the leg rather than deriving it.

Volume of deposit = cross_section × weld_length Weight of deposit = volume × density (7.85 g/cm³ for steel)

Deposition efficiency is how much of the filler actually ends up in the joint, as opposed to lost to spatter, stub ends or flux. It varies by process:

• SMAW (stick): 62%, in a band of 60 to 65. Electrodes carry thick flux coatings and the stub ends are discarded
• FCAW (flux-core): 85%, in a band of 80 to 90
• GMAW (MIG): 95%, in a band of 90 to 98
• GTAW (TIG): 98%, in a band of 95 to 100

Those are the same four figures the welding rod calculator uses, so the two pages agree on the same joint.

For stick welding, you need to buy significantly more rod than the calculated deposit weight because 35-40% of each electrode’s weight is flux coating and stub.

Multi-pass welds (thick plate) multiply the total deposit weight and are accounted for by the fill area formula, because thicker plate means a larger V-groove cross-section. There is nothing extra to enter.

Always add 15% to the calculated order weight for grinding, restarts, and test welds.
Running out of wire on the last pass of a pressure vessel seam is not a situation you want to be in.