Weld Root Gap Calculator
A guide for welders to determine the appropriate root gap (or root opening) for a weld joint to ensure complete and consistent root penetration.
Fit-Up Parameters
Select your welding process and material thickness to get a recommended root gap range.
The Foundation of a Strong Weld: The Root Gap
The root gap, also known as the root opening, is the intentional gap left at the bottom of a weld joint before welding begins. This space is arguably the most critical aspect of joint preparation. Its purpose is to allow the welding arc and filler metal to penetrate to the bottom of the joint, ensuring a "complete joint penetration" (CJP) weld. A proper root gap is the foundation of a strong and sound weld.
Consequences of an Incorrect Root Gap
- Too Small: If the gap is too small, the arc cannot reach the bottom of the joint, leading to "lack of penetration" or "incomplete fusion." This is a serious defect that creates a built-in crack at the root of the weld, severely weakening the joint.
- Too Large: If the gap is too wide, it can be difficult to bridge with the molten metal, especially on the root pass. This often leads to "burn-through," where the metal falls through the joint, leaving a hole. It also requires more filler metal and time to fill, increasing costs.