Fillet Weld Strength Calculator
Check fillet weld capacity for shop and field connections. Enter leg size, length, electrode, and load direction to get ASD and LRFD strengths from AISC Chapter J throat equations.
Fillet Weld Capacity
How Fillet Weld Capacity Is Calculated
Fillet strength is governed by the effective throat, not the leg face you see on the drawing. AISC uses a throat of 0.707 × leg size, then applies electrode strength and a direction factor from J2.4. This tool returns both ASD (Ω = 2.00) and LRFD (ϕ = 0.75) so you can match the specification method on the job.
How to use this calculator
- Select the fillet leg size called out on the detail (commonly 3/16″ or 1/4″ for clip angles and seat connections).
- Enter weld length in inches for one continuous segment. Use Pair when both sides of a plate or angle are welded.
- Pick the electrode classification (E70XX is the shop default for carbon steel) and whether load is parallel or transverse to the weld axis.
Detailing notes that affect capacity
Unit strength for E70 at parallel load is about 0.928 kips/in per 1/16″ of leg. A 3/16″ fillet is therefore roughly 2.78 kips/in ASD before length and pair multipliers. Transverse loading (90°) increases nominal weld strength by up to 50% via the sin1.5θ term — useful on end-loaded plates, but do not apply it blindly when the force path is mixed. Also confirm base-metal strength and minimum/maximum fillet sizes in J2.2; a 5/8″ fillet on 1/4″ plate is not a free upgrade if the plate tears first.
FAQ
Is this throat strength or base-metal strength?
Throat (weld metal) only. Check shear rupture and block shear on the connected element separately when the plate is thin or the weld is short.
When should I use Pair (Double)?
When both faces are welded with the same length and size — for example double-sided fillets on a gusset or angle. If lengths differ, run two single calculations and add the results.
Does intermittent weld length include skips?
Enter the sum of the actual weld segments, not the overall joint length. A 3-6 intermittent pattern on a 24″ edge is 12″ of weld, not 24″.
Why is LRFD higher than ASD?
Different safety formats: LRFD multiplies nominal strength by ϕ = 0.75; ASD divides by Ω = 2.00. Compare like-to-like with the load combination method on your drawings.