Welding Calculator — Heat Input & Weld Time
Enter arc voltage, welding current, travel speed, and weld length to calculate heat input per millimetre (kJ/mm), total arc energy, arc power, and how long the weld will take. The thermal efficiency factor is applied automatically for the selected welding process.
Welding process
V
A
mm/min
mm
Heat delivered to the weld per unit length (η × arc energy)
- 1
Arc power
22 V × 160 A = 3,520 W - 2
Arc energy per mm
3,520 × 60 ÷ 200 mm/min = 1,056 J/mmMultiply by 60 to convert mm/min travel speed into seconds per mm. - 3
Heat input (η × arc energy ÷ 1000)
0.8 × 1,056 ÷ 1000 = 0.845
How does this calculator work?
Heat input H = η × V × I × 60 / v [kJ/mm] where V = voltage, I = current, v = travel speed (mm/min), η = thermal efficiency (0.60–1.00 by process). For example: 22 V, 160 A, 200 mm/min SMAW → arc energy = 3.96 J/mm × 0.80 = 3.17 kJ/mm heat input.
Formula
How this is calculated
Weld heat input (H, in kJ/mm) is a key quality parameter: too low and fusion is poor; too high and you risk grain growth, distortion, and HAZ toughness loss. It is calculated in two steps. First, arc energy per unit length Q = (V × I × 60) ÷ v is derived from the fundamental relationship energy = power × time, where travel speed v (mm/min) is converted into time per millimetre. Then a process-specific thermal efficiency factor η converts arc energy into the heat actually deposited: H = η × Q.
Efficiency factors follow EN 1011-1 / ISO 3834 guidance: SMAW, GMAW, and FCAW are typically η = 0.80; GTAW (TIG) and plasma arc are η = 0.60 because more heat radiates away from the arc column; submerged arc (SAW) is η = 1.00 because the flux blanket traps virtually all arc energy. AWS D1.1 uses arc energy without an efficiency factor — that value is also shown for reference.
Weld codes often specify minimum and maximum heat input limits per material and thickness. For carbon steels the typical upper limit is 3.5–5 kJ/mm for structural work; stainless steels and high-strength steels often require lower limits to control sensitisation or avoid over-tempering the HAZ. Always verify limits in your applicable welding procedure specification (WPS).
Frequently asked questions
Arc energy Q is the electrical energy per mm of weld: Q = (V × I × 60) / v [J/mm]. Heat input H = η × Q accounts for the fact that not all arc energy reaches the weld pool — some is radiated, conducted into the atmosphere, or lost to electrode heating. AWS D1.1 uses arc energy; EN 1011-1 uses heat input.
Higher heat input increases the width and depth of the heat-affected zone (HAZ) and slows cooling. This can reduce HAZ hardness and toughness in high-strength steels, cause distortion in thin plates, and sensitise stainless steels to intergranular corrosion. Lower heat input can cause lack of fusion, porosity, or cold cracking, especially in thicker sections that need preheat.
Travel speed is in the denominator — doubling it halves the heat input. It also directly determines weld time. Inconsistent travel speed is one of the most common causes of variable bead profile and out-of-specification heat input. Mechanised welding is preferred for tight heat input tolerances.
Also known as
TG we-Calculate Editorial Team. (2026). Welding Calculator — Heat Input & Weld Time [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/welding-calculator
TG we-Calculate Editorial Team. "Welding Calculator — Heat Input & Weld Time." TG we-Calculate. 2026. https://we-calculate.com/calculator/welding-calculator.
TG we-Calculate Editorial Team, "Welding Calculator — Heat Input & Weld Time," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/welding-calculator
@misc{wecalculate_welding_calculator, title = {Welding Calculator — Heat Input & Weld Time}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/welding-calculator}}, year = {2026}, note = {TG we-Calculate} }
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