Usually, most of the welding helmets available in the market will be found to have dimensions of 3.5-1.75 inches as length and height, respectively. These dimensions are considered to be sufficient for ordinary welding jobs. But if you feel performing under-car welding, then you might have to look for the larger lens, preferably with dimensions such as 3.5 by 2.5 inches, which will give you a broader view and will make the welding job a lot easier for you.