What is a normal heat input range for welding mild steel?

Most mild steel welds land between about 0.5 and 2.5 kJ/mm . Thin sheet: about 0.3 to 1.0 kJ/mm General plate work: about 1.0 to 2.5 kJ/mm Thick plate with submerged arc: 3 kJ/mm or more These are guides only. The limits in your WPS or code always come first.

How do you convert kJ/mm to J/in?

Multiply by 25,400 . 1 kJ/mm = 25,400 J/in 1 kJ/mm = 25.4 kJ/in To go the other way, divide J/in by 25,400. Example: 1.056 kJ/mm × 25,400 = about 26,822 J/in.

Is heat input measured per pass or for the whole weld?

Per pass. Every run has its own volts, amps, and travel speed, so each one gets its own number. Codes set limits pass by pass, not for the joint as a whole. On thick joints, write down the value for each run and watch the highest one.

What is the difference between arc energy and heat input?

Arc energy is the raw power over speed: (V × I) ÷ S . It ignores heat lost to the air and spatter. Heat input multiplies that by the thermal efficiency k , so it shows the heat that really enters the joint. EN ISO 1011-1 uses the k factor. ASME IX and AWS use arc energy and still call it heat input. The arc energy number is always the bigger one, so state which method you used.

How do you lower heat input without losing fusion?

Try these, in this order: Travel a bit faster, since speed has the biggest effect Use stringer beads instead of wide weaves Trim voltage and amps slightly Use more small passes instead of a few large ones Keep interpass temperature down Then cut and etch a test coupon to prove fusion is still good.

What is the maximum heat input for duplex stainless steel?

For 2205 duplex, most makers ask for roughly 0.5 to 2.5 kJ/mm . Too low cools too fast and leaves too much ferrite, which hurts toughness and corrosion resistance. Too high holds the metal hot too long and can form brittle sigma phase. Check the steel maker's data sheet, since limits change with thickness and grade.

What heat input should be used on 304 or 316 stainless steel?

Many shops keep austenitic stainless under about 1.5 kJ/mm . Stainless holds heat and moves a lot, so high heat input brings warping, wide discoloured HAZ, and a risk of carbide forming at the grain edges. Low heat, fast travel, and cool interpass temperatures give the best result.

How does heat input affect cooling time t8/5?

t8/5 is the time the weld takes to cool from 800 °C to 500 °C. That range decides how the steel hardens. Higher heat input = slower cooling = longer t8/5 = softer weld, but bigger grains Lower heat input = faster cooling = short t8/5 = harder, more brittle, more crack risk Preheat and plate thickness change t8/5 too.

Does high heat input cause more distortion?

Yes. More heat makes more metal expand, and all of it shrinks as it cools. That pulling causes warping, angular twist, and bowing. To cut distortion, drop the heat input, use smaller passes, weld in a balanced order on both sides, and clamp the parts.

How do you calculate heat input for pulsed MIG welding?

Use true instantaneous power , not average volts times average amps. In pulsed welding the peaks of voltage and current line up, so multiplying the two averages can be off by 20% or more. Use a meter or power source that samples volts and amps together and reports average power in watts, then divide by travel speed.

Does weaving increase heat input?

Yes. Weaving slows how fast the torch moves along the joint , and slower forward travel means more heat per millimetre. Always measure travel speed straight down the weld line, not along the zigzag path. A wide weave can easily double heat input compared to a stringer bead.

What is the run-out length method for stick welding?

It is a quick way to control heat input with a stick electrode without timing the run. You burn one electrode and measure the length of weld it made. A short run means the heat was packed into less length, so heat input is high. A long run means lower heat input. WPSs often list a minimum run-out length for a given electrode size and amperage.

How much can heat input change from a qualified WPS?

If the weld needs impact testing, going above the qualified heat input usually means you must requalify the procedure. ASME IX treats that rise as an essential variable. For welds with no impact test, there is often more room, but many project specs still set hard upper and lower limits. Read the code and the job spec before you change volts, amps, or travel speed.

Does heat input control weld penetration?

Only in part. Current (amps) drives penetration the most. Voltage mainly widens the bead, and travel speed spreads or packs the heat. Two welds can share the same heat input yet look very different. High amps with fast travel digs deep, while low amps with slow travel makes a wide, shallow bead.

Welding Heat Input Calculator - kJ/mm, J/in, HAZ, ISO & ASME

Quantity	Value
Arc power (V × I × k)	—
Heat input (kJ/mm)	—
Heat input (kJ/in)	—
Heat input (J/mm)	—
Heat input (J/in)	—
Travel speed	—

Introduction

Heat input tells you how much heat a weld puts into the metal. This welding heat input calculator returns that value in kJ/mm and J/in. Type in your arc voltage, welding current, and travel speed, then press Calculate.

Heat input matters because too much heat can weaken the metal and make the heat-affected zone (HAZ) too big. Too little heat can leave weak or unfused welds. Welding codes like EN ISO 1011-1 and ASME IX / AWS often set limits, and this tool supports both. EN ISO uses a thermal efficiency factor (k) for your process, such as TIG, MIG/MAG, stick, flux cored, or submerged arc. ASME IX and AWS use arc energy with no k factor.

The tool also:

Works in metric or imperial units
Finds your travel speed from weld length and time
Shows the full formula and each step of the math
Rates your HAZ as low, medium, or high
Graphs how heat input changes with travel speed

Use it to check a weld procedure (WPS), plan a test weld, or study for a welding class.

How to use our Welding Heat Input Calculator

Enter your arc voltage, welding current, travel speed, and welding process. The calculator gives you the weld heat input in kJ/mm and J/in, plus a HAZ (heat-affected zone) rating, a step-by-step solution, and a chart.

Welding Standard: Pick EN ISO 1011-1 to use a thermal efficiency factor (k), or ASME IX / AWS to skip it (k = 1.00).

Unit System: Choose Metric for kJ/mm or Imperial for J/in. Both units always show in the results.

Arc Voltage (V): Type the volts at the arc, like 24.

Welding Current (A): Type the amps used on the run, like 220.

Travel Speed: Type how fast the torch moves and pick the unit (mm/min, in/min, and more). It must be more than zero.

Weld Length and Weld Time (optional): Don't know your speed? Open the drop-down box, enter the weld length and the time it took, then click "Apply to Calculator" to fill in the travel speed for you.

Welding Process: Choose TIG, MIG/MAG, FCAW, MMA, SAW, PAW, or Custom. This sets the k value on its own.

Thermal Efficiency (k): This fills in from your process. Pick "Custom" if you want to type your own value between 0 and 1.

Click Calculate to see your results. Use Try Example to load sample values, or Clear to start over. You can also drag the sliders in the visualizer to see how volts, amps, and speed change heat input right away.

What Is Welding Heat Input?

Heat input is the amount of heat that goes into a weld for each unit of weld length. It is found from three things: arc voltage, welding current, and travel speed. Heat input is usually written in kilojoules per millimetre (kJ/mm) or joules per inch (J/in).

Put simply: more volts and more amps push more heat in. Moving the torch faster spreads that heat over more length, so the heat input drops.

The Heat Input Formula

The basic equation is:

H = (V × I × k × 60) ÷ S

H = heat input (J/mm, or kJ/mm when you use the 0.06 factor)
V = arc voltage (volts)
I = welding current (amps)
k = thermal efficiency of the process
S = travel speed (mm/min or in/min)

In metric work the formula is often shown as H = (V × I × k × 0.06) ÷ S, which gives the answer straight in kJ/mm.

Thermal Efficiency (k)

Not all arc energy ends up in the metal. Some is lost to the air, the shielding gas, and spatter. The k factor accounts for that loss. EN ISO 1011-1 lists these values:

TIG (GTAW) and Plasma (PAW): k = 0.6
MIG/MAG (GMAW), Flux Cored (FCAW), Metal Cored (MCAW), Stick (SMAW/MMA): k = 0.8
Submerged Arc (SAW): k = 1.0

Two Standards, Two Answers

EN ISO 1011-1 uses the k factor, so the result is the true heat that reaches the joint. ASME IX and AWS use arc energy only, with no efficiency factor (k = 1.0). The ASME number is always higher for the same weld. Always say which method you used when you record a weld, or your numbers will not match someone else's.

Why Heat Input Matters

Heat input changes the metal around the weld. This zone is called the heat-affected zone (HAZ). Get it wrong and the joint can fail.

Too low: the weld cools fast. This can cause hard, brittle spots, cracking, lack of fusion, and hydrogen cracks.
Too high: the weld cools slowly. Grains grow large, toughness drops, and you can get more distortion, sagging, and a wide soft HAZ.

This is why welding procedure specifications (WPS) set heat input limits. Stainless steels, duplex, high-strength low-alloy steels, and thin sheet are the most fussy.

HAZ Ranges Used Here

Low: under 1.5 kJ/mm, small HAZ, fast cooling
Medium: 1.5 to 3.0 kJ/mm, common range for many steel jobs
High: over 3.0 kJ/mm, wide HAZ, slow cooling, watch for grain growth

These are general guides. Your WPS, code, or steel maker's data sheet always comes first.

Finding Travel Speed

If you do not know your travel speed, time a run and measure it. Divide weld length by weld time. For example, a 500 mm weld made in 100 seconds gives 5 mm/s, which is 300 mm/min.

Tips for Better Results

Read voltage and current while the arc is burning, not from the machine's preset dial.
Use the same units all the way through. Mixing mm/min with in/min is the most common mistake.
For weaving, measure the true forward travel speed, not the side-to-side path length.
Heat input rises fast when you slow down. Cutting travel speed in half doubles the heat input.
Record heat input for each pass on thick joints, since limits often apply pass by pass.

Heat Input Calculator