Weld Filler Metal Weight Calculator

Ordering the right amount of filler metal before a job — and not running out mid-pass — requires 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 (equal legs, size = 0.7 × plate thickness is the minimum for structural): cross_section = 0.5 × leg_size²

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

Deposition efficiency — how much of the filler material actually ends up in the joint versus lost to spatter, stub ends, or flux — varies by process:

• SMAW (stick): 60-65% (electrodes have thick flux coatings, stub ends are discarded)
• GMAW (MIG): 93-98%
• GTAW (TIG): 97-99%
• FCAW (flux-core): 80-90%

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 — thicker plate means a larger V-groove cross-section, not additional manual input.

Always add 10-15% 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.