Weld Calculations

How to Calculate Weld Deposition Rate, Travel Speed, and Heat Input

The five core welding calculations every fabricator runs, worked from raw inputs like wire feed speed, amperage, and joint geometry to finished numbers.

Deposition rate is the foundation number. The formula is deposition rate (lb/hr) equals wire feed speed (in/min) times cross-sectional wire area (in squared) times steel density (0.283 lb/in cubed) times 60, then times deposition efficiency. For 0.045 in solid wire, area is 0.00159 in squared. At 300 in/min WFS: 300 times 0.00159 times 0.283 times 60 equals 8.1 lb/hr gross, and at 0.98 efficiency you deposit 7.9 lb/hr. Flux-cored drops efficiency to 0.82 to 0.88, so the same WFS deposits closer to 6.9 lb/hr. The Weld Deposition Rate calculator does this from WFS and diameter directly.

Weld metal required starts from joint geometry, not the machine. Compute cross-sectional area of the weld, then multiply by length and density. A single-V groove on 1/2 in plate with a 60 degree included angle and 1/16 in root has an area near 0.083 in squared per inch of length. Over a 40 in seam that is 3.32 in cubed, or 0.94 lb of steel at 0.283 lb/in cubed. Add 10 to 15 percent for reinforcement and spatter. A 3/8 in fillet weld is simpler: area equals 0.5 times leg squared, so 0.5 times 0.375 squared equals 0.070 in squared. The Weld Metal Required calculator handles both groove and fillet profiles.

Travel speed ties deposition to the joint. Travel speed (in/min) equals deposition rate (lb/hr) times 1 over weld metal per inch (lb/in), converted through 60 minutes. If you deposit 7.9 lb/hr and a 3/8 fillet needs 0.070 in squared times 0.283 equals 0.0198 lb/in, then travel speed equals 7.9 divided by 60 divided by 0.0198, which is 6.6 in/min. Run faster and the fillet undersizes; run slower and you overweld. The Weld Travel Speed calculator inverts this when you already know your target leg size and current amperage.

Heat input governs metallurgy and distortion. The formula is heat input (kJ/in) equals volts times amps times 60, divided by travel speed (in/min) divided by 1000, times thermal efficiency. GMAW efficiency runs 0.80 to 0.90; SAW reaches 0.95; GTAW sits near 0.60. At 28 V, 250 A, 12 in/min travel, and 0.85 efficiency: 28 times 250 times 60 equals 420,000, divided by 12 equals 35,000, divided by 1000 equals 35, times 0.85 equals 29.8 kJ/in. Most carbon steel procedures cap heat input between 20 and 50 kJ/in. The Weld Heat Input calculator flags when you exceed a WPS limit.

Arc-on time converts pounds into clock time. Arc-on time (min) equals weld metal weight (lb) divided by deposition rate (lb/hr) times 60. That 0.94 lb groove at 7.9 lb/hr needs 0.94 divided by 7.9 times 60 equals 7.1 minutes of actual arc time. This is pure burn time, not shift time. It feeds directly into any labor estimate and pairs with operator factor to get real elapsed hours. The Arc-On Time calculator returns this in seconds and minutes so you can total a multi-pass joint.

Multi-pass joints require summing per-pass volumes, not scaling one pass. A 1 in thick double-V weld might take 9 passes, each depositing roughly 0.11 lb over its own travel length. Total weld metal is the sum, near 1.0 lb per inch of seam, so a 24 in seam consumes 24 lb of wire. At 8 lb/hr that is 3 hours of arc time before you add stops for slag removal, wire changes, and repositioning. Always compute each layer's cross-section separately, because the fill passes are wider than the root and cap.

Wire feed speed to amperage is the input most people guess wrong. For 0.045 solid wire in spray transfer, expect roughly 250 to 400 in/min WFS producing 220 to 320 A. Read WFS off the machine, not the amp meter, because voltage and stickout shift the amp reading by 20 to 40 A at fixed WFS. Deposition rate is driven by WFS and diameter, so anchor every calculation to measured WFS. If you only have amps, back into WFS with the wire's published burn-off curve before you touch the deposition or travel speed math.

Sanity-check every result against one another. If deposition rate, travel speed, and weld metal per inch do not reconcile, one input is wrong. Deposition rate divided by 60, divided by weld metal per inch, must equal travel speed within a few percent. When a 3/8 fillet calculation returns 15 in/min at 7.9 lb/hr, the leg is really coming out near 1/4 in, not 3/8. Cross-checking the Weld Deposition Rate, Weld Travel Speed, and Weld Metal Required outputs against each other catches unit slips before they reach the shop floor.

Published 2026-07-01.