Fillet Weld Calculator

What the fillet weld calculator does

A fillet weld carries load through its throat, the shortest distance from the root to the weld face. For an equal leg fillet, the throat is 0.707 times the leg. The fillet weld calculator multiplies the throat by the length to get the weld area, applies the weld metal shear strength of 0.60 times the electrode strength, and then the LRFD or ASD factor, following AISC 360.

Fillet weld formula

The AISC weld metal strength for a fillet weld loaded in shear along its length:

For E70 electrodes this gives the familiar 1.392 kips per inch for each 1/16 inch of leg in LRFD, and 0.928 kips per inch in ASD.

Fillet weld calculator example

A 1/4 in E70 fillet weld, 6 in long, LRFD:

That is 5.568 kips per inch, or 148.6 kN in total. In ASD the same weld carries 3.712 kips per inch, so a 20 kip load needs 5.39 in of weld.

How to use the fillet weld calculator

Enter the weld leg size in inches, such as 0.25 for a 1/4 in fillet, and the total effective length of weld. Pick the electrode class, usually E70XX, and the design method you use. Add the load to have the fillet weld calculator work out the length needed. Use the effective length: leave out starts and stops that do not reach full size.

Reading fillet weld capacity

The result is the weld metal strength only. The connected parts must also carry the load along the weld, and thin base metal can control before the weld does. AISC also sets minimum fillet sizes by the thicker part joined, maximum sizes along edges, and a minimum length of four times the leg. Welds loaded at an angle to their axis can carry more, up to 1.5 times for a transverse weld, which this conservative result leaves out.

When to use a weld strength calculator

• Sizing fillet welds on brackets and clips
• Checking how long a weld must be for a load
• Comparing E60, E70, and E80 electrodes
• Converting between LRFD and ASD capacities
• Teaching how weld size and length trade off

Common fillet weld calculator mistakes

• Using the leg as the throat. The throat is 0.707 times the leg.
• Counting starts and stops. Use only full size effective length.
• Mixing LRFD and ASD. Match the method to your loads.
• Skipping the base metal. Thin plates can govern.

Tips for fillet weld capacity

• Prefer a longer, smaller weld over a short, large one.
• Wrap welds around corners where allowed to add length.
• Have structural welds checked by a qualified engineer.

Related steel tools

Weld checks sit beside member checks. The steel beam size calculator sizes the beam, the stress calculator checks the plate, and the flat bar weight calculator weighs the plates and straps.

Fillet weld size calculator rules

Bigger is not always better. A fillet weld much larger than needed adds heat, distortion, and cost, and the weld volume grows with the square of the leg size: a 1/2 in fillet needs four times the metal of a 1/4 in fillet but carries only twice the load per inch. That is why designers often prefer a longer small weld to a short large one. AISC sets a minimum size by the thicker part, for example 3/16 in for parts over 1/4 in up to 1/2 in thick, so that the weld cools slowly enough to fuse properly. Along the edge of a plate thicker than 1/4 in, the maximum size is the plate thickness minus 1/16 in. Check the plate itself in tension or shear with the stress calculator.

Weld strength formula for LRFD versus ASD

Both methods start from the same nominal strength Rn. LRFD compares factored loads, larger than service loads, with φRn, while ASD compares service loads with Rn divided by a safety factor. For welds the two give the same design for a typical mix of dead and live load, which is why the LRFD value is exactly 1.5 times the ASD value. Use the method that matches your load calculations, and keep it consistent through the connection, including any beam sized with the steel beam size calculator.

Fillet weld strength per inch

E70XX fillet weld strength per inch of length:

Related Calculators