Preheat calculator
Find the governing temperature for both sides of the joint.
Choose the conditions to see the result.
Share your project details and supporting records. We’ll review the route and scope before preparation.
Method, scope & reference AWS D1.1 / D1.1M:2025
2025 base edition with July 28, 2026 errata. AMD1 not included.
What determines preheat?
The applicable requirement depends on the base metal classification, the welding process and its conditions, thickness at the weld, initial temperature, and any applicable hydrogen control provisions. When the two sides have different requirements, the higher minimum governs the joint.
The input called “thickest component at the weld” means the thickness of the thickest joined member at the point being welded. It is not the weld size or a general plate thickness elsewhere in the assembly.
The material and process presets address the preheat calculation only. Separate Table 5.6 material group, grade and thickness eligibility conditions may still apply to the selected steel and the overall WPS.
Hydrogen and project conditions
A reduced temperature category based on diffusible hydrogen requires a qualifying A4.3 test result for the relevant condition. If that evidence is not available, leave the optional field unset; do not infer it from a common electrode name or storage and handling records. Project requirements can impose a higher minimum or an independent maximum interpass temperature.
This tool is limited to listed material mappings and supported processes. It does not calculate carbon equivalent, decide every hydrogen or restraint control, or review the full WPS and contract.
Reference points: AWS D1.1/D1.1M:2025 Table 5.11 and Clause 5.7 for preheat requirements, Clause 7.6 for applicable temperature provisions, and Table 5.6 for base metal eligibility. Review the applicable table notes and contract requirements.
Preheat questions
Does a filler metal such as E7018 determine preheat by itself?
No. Base metal classification, thickness, process conditions, initial temperature and applicable hydrogen requirements all matter. A consumable's name alone does not establish the base metal preheat requirement.
Why do I have to enter the initial temperature?
The starting metal temperature is part of the condition check. The entered value should represent the base metal condition before welding, using the selected SI or US customary units.
Can the project maximum interpass temperature change the minimum?
No. A specified maximum interpass temperature is a separate upper limit. The tool reports it separately from the governing minimum preheat.