Heat Input Calculator

What Your Heat Input Means

Heat input measures the energy transferred to the base metal per unit length of weld, expressed in kJ/in or kJ/mm. It is a function of voltage, amperage, and travel speed. Higher heat input means a wider heat-affected zone (HAZ), slower cooling, and greater risk of grain growth and reduced toughness in the base metal.

Under D1.1:2025, heat input restrictions apply only to quenched and tempered (Q&T) steels per Clause 7.7. For these steels (A514, A517), the producer's maximum heat input recommendations must be followed to preserve the Q&T mechanical properties. ASTM A913/A913M is explicitly exempt from Clause 7.7. For all other structural steels (A36, A572, A992, A500, Groups I through III), D1.1 imposes no numeric kJ/in ceiling.

Even without a code-mandated limit, controlling heat input is good practice. Excessive heat input on thin sections can cause burn-through and distortion. On thick sections, insufficient heat input leads to fast cooling rates that increase hydrogen cracking risk. Pair your heat input with the preheat calculator and carbon equivalent to get the full thermal picture.

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