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Weld Heat Input Calculator - AWS D1.1 & ASME IX Compliant Heat Input

Calculate heat input in kJ/inch from voltage, amperage, and travel speed per welding code requirements

Free weld heat input calculator for structural, pressure vessel, and pipeline welding. Heat input is a critical variable in weld procedure qualification under AWS D1.1, ASME Section IX, and API 1104. Exceeding the qualified heat input range means your WPS is invalid and your welds may not meet mechanical property requirements. This calculator computes heat input using the standard formula: Heat Input (kJ/in) = (Voltage × Amperage × 60) / (Travel Speed × 1000). Enter your actual welding parameters - arc voltage, welding current, and travel speed in inches per minute - and get the heat input value you need for your procedure qualification record (PQR) or production weld log. The calculator supports all common arc welding processes: SMAW, GMAW (MIG), FCAW, GTAW (TIG), and SAW. For processes with pulsed current, it handles both average and peak/background calculations. Results include the heat input value, a comparison against typical code-qualified ranges for common base metals, and guidance on how changing each variable affects the result. For carbon steel and low-alloy work under AWS D1.1, heat input directly controls cooling rate, grain size, and hardness in the heat-affected zone (HAZ) - get it wrong and you create hard, crack-susceptible microstructures.

Pro Tip: Travel speed is the hardest variable to measure accurately on a real weld, and it has the biggest impact on heat input. A welder who slows from 8 IPM to 6 IPM increases heat input by 33% - potentially exceeding the qualified range. On critical code work, mark the joint in 6-inch increments and time each segment with a stopwatch. For pipeline welding, some inspectors use a "bug-on-a-wire" travel speed calculator that measures arc time over a known distance. Accurate travel speed measurement is the key to staying within your WPS limits.

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Weld Heat Input Calculator
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How It Works

  1. Select Welding Process

    Choose your welding process: SMAW (stick), GMAW (MIG), FCAW (flux-core), GTAW (TIG), or SAW (submerged arc). The process determines the thermal efficiency factor if your code requires net heat input rather than arc heat input.

  2. Enter Arc Voltage

    Input the measured arc voltage during welding. This is not the machine's set voltage - it is the actual voltage measured at the arc during welding. For SMAW, typical values are 20-30V. For GMAW spray transfer, 26-34V. For GTAW, 10-18V.

  3. Enter Welding Current

    Input the measured welding amperage. For constant-current processes (SMAW, GTAW), this is set on the machine. For constant-voltage processes (GMAW, FCAW), measure it with a clamp-on ammeter during welding because actual amps vary with wire feed speed and stickout.

  4. Enter Travel Speed

    Input travel speed in inches per minute. Measure this in the field by timing a known weld length. For multi-pass welds, measure each pass separately as travel speed often differs between root, fill, and cap passes.

  5. Review Heat Input and Code Compliance

    Get the calculated heat input in kJ/inch and compare against your WPS qualified range. The calculator shows whether you are within limits and how much margin you have before exceeding the maximum or minimum qualified heat input.

Built For

  • Welding inspectors verifying that production welds meet WPS heat input limits
  • Welding engineers preparing procedure qualification records for AWS D1.1 or ASME IX
  • Pipeline welders logging heat input for API 1104 compliance on each pass
  • Fabrication shops training welders on the relationship between parameters and heat input
  • QA/QC departments auditing welder parameter logs against qualified WPS ranges

Frequently Asked Questions

Heat Input (kJ/in) = (Voltage × Amperage × 60) / (Travel Speed in IPM × 1000). For example: 28V, 250A, 10 IPM gives (28 × 250 × 60) / (10 × 1000) = 42 kJ/in. Some codes require a thermal efficiency factor: 0.8 for SMAW, 0.8 for GMAW, 0.6 for GTAW. Net heat input = arc heat input × efficiency. AWS D1.1 uses arc heat input (no efficiency factor) in most cases.
Heat input controls the cooling rate of the weld and heat-affected zone (HAZ). High heat input means slow cooling, which can cause grain growth and reduced toughness in quenched and tempered steels. Low heat input means fast cooling, which can create hard, brittle martensite in the HAZ that is susceptible to hydrogen cracking. Every WPS has a qualified heat input range that produces acceptable mechanical properties. Staying within that range is a code requirement, not a suggestion.
For mild steel (A36, A992) under AWS D1.1, typical heat input ranges are 25-65 kJ/in for SMAW, 20-55 kJ/in for GMAW, and 30-80 kJ/in for SAW. For quenched and tempered steels like A514, maximum heat input is often limited to 45-55 kJ/in to prevent HAZ softening. For weathering steels and high-strength low-alloy grades, the range narrows further. Always refer to your qualified WPS for the specific range.
Travel speed has an inverse relationship with heat input. Halving your travel speed doubles the heat input. Going from 10 IPM to 8 IPM increases heat input by 25%. This is why travel speed measurement is critical on code work. Welders who "slow down to make it look pretty" on a cap pass can easily exceed the maximum qualified heat input, especially on quenched and tempered steels where the limit is tight.
It depends on the code and material. AWS D1.1 requires heat input tracking when welding quenched and tempered steels or when the WPS has a maximum heat input limitation. ASME IX requires it whenever essential variable ranges are specified in the WPS. API 1104 requires it for all pipeline welds. For routine mild steel structural welding under D1.1 prequalified WPS, heat input is not explicitly tracked but the parameters must still fall within prequalified ranges.
Disclaimer: This calculator provides heat input values based on the standard arc energy formula. Actual metallurgical effects depend on base metal chemistry, preheat temperature, interpass temperature, joint geometry, and weld sequence. All code-critical calculations should be verified by a qualified welding engineer (CWEng) or certified welding inspector (CWI). This tool does not replace WPS qualification testing.

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