The heat input is measured in which units?

• A. Volts
• B. Joules per inch (J/in)
• C. Amps
• D. Watts

Answer: (B)

Heat input is about how much energy is delivered to the weld per length of the joint, not the instantaneous electrical values. Since welding power (voltage times current) is energy per second, you get heat per inch only when you relate that power to how fast you move along the weld. That gives energy per unit length, measured in joules per inch (J/in). Volts and amps describe electrical conditions, not how much energy ends up per inch of weld, and watts is power (energy per second) without accounting for how much length you cover per second, so it doesn’t directly express heat input per length. In practice, engineers use J/in (or kJ/in) to compare heat input effects on bead shape, penetration, and metallurgical changes.