You posted under the topic of AWS D1.1, so I assume you are welding to that standard/code. Table 4.5 lists the minimum fillet weld size based on material thickness. The load being transmitted by the fillet weld is not taken into consideration by table 4.5. For that, the engineer has to calculate the require fillet throat size based on .3 X TS of the filler metal, but the load on the base metal can't exceed .4 X the YS of the BM or .6 X the TS of the base metal.

In general, using a 70 ksi filler metal, the fillet weld can sustain a shear load of 0.927 kip per 1/16 leg per inch of length. Put another way: a 1/4 inch fillet weld is good for 4X0.927 kip per inch of weld length or 3700 pounds per inch of weld.

This is based on my recollection and at my age you can't get very far on memory alone. That why we have engineers to do the number crunching for us.

Best regards - Al