Weld size from load calculator

Reviewed by the CalculatorHub team, edited by James Graham. Method: a standard formula rather than a jurisdiction-specific rule. How we document and test our methods. Last verified 2026-06-22.

The Weld size from load calculator computes weld size from load from the relation leg = F / (0.707 L tau). It takes 3 inputs (load in N, weld length in m, allowable shear in Pa) and returns the required leg size in m. These tools are written for engineering students, technicians, draftspeople and practising engineers who need a quick quantitative answer part-way through a larger piece of work, whether the question in front of them is structural, mechanical, fluid, thermal, electrical or a matter of site quantities, and who want to see how the numbers behave before committing more effort to a given arrangement. Enter your values below and the result updates instantly, and you can share a permalink that pre-fills the exact calculation. Keep every input in one consistent unit system before you enter it, since a mismatched length, area, pressure, flow or electrical unit is the usual reason a result lands orders of magnitude away from expectation; be explicit about the assumptions behind each figure, whether those are geometry and material properties or flow, thermal and operating conditions; and carry no more precision into the next step than the least certain input justifies. For example, with load = 0 N, weld length = 0.2 m, allowable shear = 100000000 Pa, the required leg size works out to 0 m, and the worked example further down the page shows every step so you can follow the arithmetic and reproduce it by hand. This is a standard formula rather than a jurisdiction-specific rule, so it does not depend on an external rate or schedule, and the figure above each result carries the date it was last verified. These are working calculations that model one idealised condition at a time, so they carry none of the safety margin, the full range of loads and operating states, or the real material, fabrication and installation behaviour that a finished structure, machine or system has to tolerate, and the qualified engineer responsible for the project still has to make the call.