Fillet Welds

You should always refer to some standard to dimension the welds on critical applications. But, for a start to you, you should dimension the weld by considering the resistant section as the area defined by the throat plane by the lenght of the weld. Always calculate it to welds with equal legs, it's easier and in most of situations will give you the most economically rewarding welds. Usually, weld leg is defined by the possible by the member wall thickness, throat is calculated, and weld lengh is a consequence of the first. A little forward and aft in this calculation is sometimes required. Position welds in a way this resistant section is submitted by shear stress, not tension. It will save your design from aligning your working load with the remaining stress resulting from welding - specially important where stress relief after weld is not possible. The rest my friend, is structural mechanics, calculating efforts, material stress, etc. BTW: throat - the minimum distance between the weld root and the weld face.