Welding

Weld Heat Input Calculator

Calculate heat input in kJ/mm based on amps, volts, and travel speed.

Input Parameters

Units:
V
A
in/min
in

Results

Enter welding parameters and click Calculate

What is Weld Heat Input?

Weld heat input is the amount of energy transferred to the workpiece per unit length of weld. It's a critical parameter that affects cooling rate, mechanical properties, and distortion.

Controlling heat input is essential for meeting code requirements, preventing cracking, and achieving desired weld properties.

How to Use

  1. Select your welding process
  2. Enter arc voltage (from machine or measured)
  3. Enter welding current (amperage)
  4. Enter travel speed
  5. Optionally enter material thickness for context
  6. Click Calculate for heat input

FAQs

Heat input is the energy per unit length (kJ/in or kJ/mm) delivered to the weldment. It directly affects cooling rate, HAZ size, distortion, and mechanical properties. Too high causes grain growth and reduces strength. Too low can cause cracking in hardenable steels.

Arc efficiency varies by how the heat transfers to the workpiece. SAW (95%) traps heat under flux. GMAW/FCAW (85%) lose some to air. SMAW (80%) has coating losses. GTAW (60%) radiates significant heat from the tungsten and has high arc voltage losses.

Preheat is typically required for: carbon equivalent > 0.40, thickness > 1" (25mm), high restraint joints, low ambient temperature, or when specified by code. It slows cooling to prevent hydrogen cracking and allows hydrogen to escape.

Check your Welding Procedure Specification (WPS) for the qualified range. General guidelines: structural steel 25-70 kJ/in (1-2.8 kJ/mm), stainless steel 20-50 kJ/in to minimize sensitization, aluminum varies widely. Many codes specify maximums.

Heat input is inversely proportional to travel speed. Double the speed = half the heat input. Slower speeds increase penetration and HAZ width but also distortion. Faster speeds are typically better if adequate fusion is achieved.

Limitations

  • • Arc efficiency values are typical - actual varies with technique
  • • Pulsed welding requires RMS values for accuracy
  • • Does not account for preheat or interpass temperature
  • • Cooling rate depends on many factors beyond heat input
  • • Always verify heat input limits per applicable code/WPS

Further Reading

Weld Heat Input Calculator: Formula & Best Practices

Calculate weld heat input in kJ/mm or kJ/in. Understand why heat input matters for weld quality and metallurgy.

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