Load Combination Calculator
Enter your nominal loads and see which ASCE 7 combination governs. Every LRFD strength case or ASD allowable case is factored and ranked, so the worst-case design load is the one staring back at you.
Loads Do Not Arrive One at a Time
A structure rarely sees just dead load, or just wind. It sees combinations — full gravity load on a windy day, or snow on the roof during an earthquake. Building codes do not ask you to add every load at full value (that would be wildly improbable); they prescribe specific factored combinations, each representing a credible worst case. The design load is whichever combination comes out largest.
LRFD vs ASD
LRFD (load and resistance factor design, also called strength design) multiplies each load by a factor — 1.2 on dead, 1.6 on live — and compares the result to the member factored strength. ASD (allowable stress design) keeps the loads near their service values, combining them with smaller factors, and compares to an allowable stress. Same loads, two bookkeeping systems; this calculator runs whichever set you pick and ranks them.
The Uplift Cases
Most combinations stack loads to find the largest downward demand. A few do the opposite — 0.9D with wind in LRFD, 0.6D with wind in ASD — deliberately using a reduced dead load. These check uplift and overturning, where wind or seismic acts upward or sideways and only the minimum reliable dead load resists it. They matter for anchors, hold-downs and light roofs.
Frequently Asked Questions
What is (Lr or S)?
The combination uses whichever of roof live load, snow or rain is largest in that slot – they rarely peak together. This tool takes the larger of the roof live and snow values you enter.
Which method should I use?
Steel and concrete are usually designed by LRFD today; wood, masonry and some foundation work still often use ASD. Use whichever your design standard and material call for – never mix factored and service loads.
Does this cover seismic overstrength?
No. The special overstrength combinations (with the omega factor) for collectors and critical elements are separate and not included here.
Related calculators
- Wind Load Calculator — the W in the combinations.
- Snow Load Calculator — the S in the combinations.
- Seismic Base Shear Calculator — the E in the combinations.
- Beam Load Calculator — apply the governing load to a member.