Engineering

Welding Heat Input Calculator

Calculate gross and net heat input for any welding process with material-specific recommendations.

Quick Answer:Heat Input (kJ/in) = (Voltage x Amperage x 60) / (Travel Speed x 1000). Multiply by process efficiency for net heat input. Keep below 50 kJ/in for carbon steel and 30 kJ/in for stainless steel.

Welding Parameters

Voltage (V)

Amperage (A)

Travel Speed (in/min)

Welding Process

Preheat Temperature (°F)

Gross Heat Input

Calculating... kJ/in

Net Heat Input

kJ/in (with efficiency)

Heat Input (Metric)

kJ/mm

Carbon Steel Limit

Recommended < 50 kJ/in

Stainless Steel Limit

Recommended < 30 kJ/in

Visual Comparison

Gross Heat Input--

Net Heat Input--

Carbon Steel Limit (50 kJ/in)50

Stainless Steel Limit (30 kJ/in)30

Expert Insight 2026 Pro Tip

Per AWS D1.1:2025 and ASME Section IX, heat input control is critical for maintaining weld quality. When welding high-strength steels (ASTM A514/A517), keep heat input between 30-60 kJ/in to prevent hydrogen-assisted cracking. For stainless steels (304/316), staying below 30 kJ/in prevents sensitization and maintains corrosion resistance. Always verify your WPS heat input limits before welding, and remember that preheat temperatures above 200°F may allow slightly higher heat inputs for carbon steels.

Frequently Asked Questions

What is heat input in welding and why does it matter?

Heat input is the amount of energy transferred per unit length of weld, measured in kJ/in or kJ/mm. It directly affects the weld's mechanical properties, microstructure, and susceptibility to defects. Too much heat input can cause grain growth, reduced toughness, and excessive distortion, while too little can lead to lack of fusion and incomplete penetration. Controlling heat input is essential for meeting code requirements and producing quality welds.

How does process efficiency affect welding heat input?

Process efficiency (also called arc efficiency) represents the fraction of electrical energy actually transferred to the workpiece. SAW has the highest efficiency at approximately 95%, while GTAW is lowest at about 60%. SMAW and GMAW are around 80%, and FCAW is about 85%. The net heat input equals gross heat input multiplied by the efficiency factor, giving a more accurate measure of energy entering the base metal.

What are the recommended heat input limits for different materials?

For low carbon steel, heat input below 50 kJ/in is generally acceptable. Stainless steel typically requires heat input below 30 kJ/in to prevent sensitization and maintain corrosion resistance. High-strength low-alloy steels often have maximum limits of 40-60 kJ/in depending on grade. Nickel alloys and duplex stainless steels may have even stricter limits. Always consult the applicable welding procedure specification (WPS) for specific limits.