Weld Rod Consumption
Calculator

It's based on the total length of weld to be made, the size (cross-sectional area) of the weld joint, and the deposition efficiency of the specific rod or electrode type, since not all of a rod's metal ends up in the finished weld.

Some material is lost as spatter, some remains as the stub end that can't be used, and for stick electrodes some is lost in the flux coating that isn't deposited as weld metal. Deposition efficiency accounts for this and is typically well under 100%, varying by process and electrode type.

Yes significantly. A fillet weld's required cross-sectional area (and therefore rod volume) scales with the square of the leg size, so increasing a fillet weld's size from 1/4 inch to 3/8 inch requires substantially more than 50% more filler metal, not just proportionally more.

Each process has a different typical deposition efficiency and deposition rate: MIG wire generally wastes less material to spatter and stub loss than stick electrodes, while TIG often uses a separate filler rod entirely with its own consumption pattern, so the electrode-to-weld-metal ratio differs by process.

Real welds include rework from defects, tack welds, and practice runs, plus rod ends that get discarded before full consumption. A common practice is to order extra material, often 10-20% above the theoretical calculation, to avoid running short mid-job.