Hi

You can check thickness of the steel and you know the size welding but not everything the same

It's pretty simple usually you see 3 standard fillet welds in America idk where you are @ but you have a 3/16 fillet weld, a 1/4 inch fillet weld, and a 5/16 fillet weld. Let's say the weld symbol says 3/8. It takes 3 fillet welds stacked like a staircase 1 1/4 inch fillet weld in the center, another 1/4 inch fillet weld on the bottom toe, and another 1/4 inch fillet weld on the top toe of the the last weld. One weld center, bottom and top it makes a 3/8 weld. To get bigger size welds you just have to stack welds in the right order.

A 3/16 weld is ran pretty fast, 1/4 weld is ran at a steady pace, and a 5/16 weld is ran a little slower just making sure that your weld toes are spread evenly. It takes time and practice get a weld fillet gauge and try making different size welds with it.