Weld Metal Calculation and Job Estimating
Accurate welding job estimating determines profitability — underestimating consumable or labor costs on a fabrication contract is a direct path to financial loss. The estimation process begins with weld metal volume calculation. For fillet welds, the theoretical weld metal cross-sectional area = leg size²/2 (for equal-leg fillets). A 3/8" fillet weld: (0.375)²/2 = 0.0703 in². Multiply by joint length: 0.0703 in² × 120" (10 feet of 3/8" fillet weld) = 8.44 in³ of weld metal. Weight: 8.44 in³ × 0.283 lb/in³ (steel density) = 2.39 lb of weld metal. Add a deposition efficiency factor: SMAW = 60–65% (the electrode coating and stub loss means only 60–65% of purchased electrode becomes weld metal); GMAW/FCAW = 85–95% (nearly all wire becomes weld metal, minor spatter). For 2.39 lb of required weld metal using SMAW at 65% efficiency: 2.39 ÷ 0.65 = 3.68 lb of electrodes purchased. Deposition rate (pounds of weld metal deposited per hour) determines labor hours: SMAW at 200A deposits approximately 5–8 lb/hour; FCAW at comparable heat input deposits 10–15 lb/hour. Labor hours = weld metal weight ÷ deposition rate × 1/arc-on-time efficiency. Full cost estimate structure: Materials (base metal: price per pound × weight, plus cutting and preparation allowance) + Consumables (filler metal, shielding gas, grinding discs, cleaning supplies) + Labor (hours × loaded labor rate including benefits, burden, and overhead) + Equipment (amortized equipment cost per job or included in overhead rate) + Overhead (facility rent, utilities, insurance, supervision) + Markup (profit margin, typically 15–25% for competitive fabrication). Always build estimates from takeoffs on actual drawings — never guess joint lengths.