Structural Load Calculator

Compute IBC 1605 load combinations — LRFD and ASD — for beams, posts, and foundations. Covers dead, live, snow, wind, and seismic loads.

Tributary Area & Geometry

Tributary Area (sq ft)

ft²

Area of floor/roof that this member supports

Stories Above

Loads (psf)

Dead Load (psf)

psf

Live Load (psf)

psf

Snow Load (psf)

psf

Wind Load (psf)

psf

Set snow = 0 for warm climates. Wind = lateral pressure on tributary facade area.

Seismic Load

Governing Load (ASD)

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Enter tributary area and loads above

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Total Dead (D)

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Total Live (L)

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Governing Combo

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Load (kips)

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Governing LRFD

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Stacked Load

IBC 1605 Load Combinations

Point load at support. Divide by beam length for uniform load (plf).

Structural Load Path

How loads travel from the roof down to the foundation. Each level accumulates the loads from above.

Load Combination Chart

All IBC 1605 load combinations shown side-by-side. The governing combination is highlighted.

LRFD vs ASD Comparison

Combination	Method	Formula	Load (lbs)	Governing

IBC Code Reference

IBC Table 1607.1 — Minimum Live Loads

Occupancy / Use	Live Load (psf)
Residential — Rooms	40
Residential — Corridors	40
Office — Offices	50
Office — Corridors / Lobbies	100
Retail — First Floor	100
Retail — Upper Floors	75
Assembly — Fixed Seats	60
Assembly — Standing	100
Garage — Passenger Vehicles	40
Storage — Light	125
Storage — Heavy	250
Roof — Ordinary Flat	20

IBC 1605.2 — LRFD Load Combinations

#	Combination
1	1.4D
2	1.2D + 1.6L + 0.5(Lr or S or R)
3	1.2D + 1.6(Lr or S or R) + (L or 0.5W)
4	1.2D + 1.0W + L + 0.5(Lr or S or R)
5	0.9D + 1.0W
6	1.2D + 1.0E + L + 0.2S
7	0.9D + 1.0E

IBC 1605.3 — ASD Load Combinations

#	Combination
1	D
2	D + L
3	D + Lr (or S or R)
4	D + 0.75L + 0.75(Lr or S or R)
5	D + 0.6W (or 0.7E)
6	D + 0.75L + 0.75(0.6W) + 0.75S
7	0.6D + 0.6W
8	0.6D + 0.7E

Ground Snow Loads — Representative Values

Region / State	Pg (psf)
FL, TX, AZ, CA Coast	0
SE States (GA, SC, AL)	5–10
Mid-Atlantic (VA, MD, NC)	15–25
Midwest (OH, IN, IL)	20–30
Northeast (NY, PA, NJ)	25–40
New England (MA, CT, ME)	30–60
Great Lakes (WI, MI, MN)	30–70
Mountain West (CO, ID, MT)	40–100+
Pacific Northwest (WA, OR)	10–50
Alaska	50–200+

Use ASCE 7 Figure 7.2-1 or local jurisdiction maps for exact Pg values.

How to Use This Calculator

Enter tributary area — the floor or roof area this member (beam, post, column) supports.

Select dead and live loads — use the preset chips or enter custom values in psf (pounds per square foot).

Add environmental loads — snow and wind loads from your local climate zone. Set snow = 0 for warm regions.

Enable seismic if required — the calculator adds 0.2D as a simplified seismic demand per IBC.

Read the governing load — the largest load combination controls design. Use this value to size beams and posts.

Key Terms

Dead Load — The permanent, self-weight of all structural and non-structural components: framing, subfloor, roofing, insulation, finishes, and fixed equipment. Dead loads do not change over time and are always present.

Live Load — Variable, movable loads from occupants, furniture, and equipment. Residential floors: 40 psf. Roof live load: 20 psf (IRC). Live loads are intermittent and vary based on use and occupancy.

Snow Load — Ground snow load (Pg) from ASCE 7 or local code, reduced by the roof slope factor (Cs). Must be added to the roof structural design load for structures in snow regions. Flat roofs carry full ground snow load.

Wind Load — Lateral and uplift forces from wind pressure on the building envelope. Wind load calculations per ASCE 7 depend on wind speed, exposure category, building height, and roof geometry.

Load Path — The continuous chain of structural members that transfers loads from the roof to the foundation: roof → rafters/trusses → beams → columns/posts → footings → soil. Every member in the path must be sized for the cumulative load above it.

Safety Factor — A multiplier applied to calculated loads (LRFD) or reduced from member capacity (ASD) to account for uncertainty in load estimation, material variability, and construction tolerances. Structural members are never designed to their theoretical limit.

Frequently Asked Questions

What is a tributary area?

The tributary area is the floor or roof surface area that a structural member (beam, column, or post) is responsible for supporting. For a simply supported beam, it equals the beam's span multiplied by half the distance to each adjacent beam on both sides.

What is the difference between LRFD and ASD?

LRFD (Load and Resistance Factor Design) multiplies each load type by safety factors greater than 1.0 before comparing to factored member capacity. ASD (Allowable Stress Design) uses unfactored loads compared to allowable stresses reduced by a safety factor. Wood (NDS) typically uses ASD; steel (AISC) supports both.

Why does the calculator multiply by (stories + 1)?

In multi-story construction, a post or column must carry the loads from every floor above plus its own level. Each story contributes roughly the same load, so a post under 2 floors above carries approximately 3× the load at a single level (2 upper floors + ground level).

How do I convert this load to beam design?

The governing load is a point load in lbs. To convert to a uniform distributed load (in plf — pounds per linear foot), divide by the beam span in feet. Use the plf value when sizing beams with span tables or structural software.

Is this calculator suitable for permit submissions?

This tool uses simplified IBC load combination methods for preliminary sizing and educational purposes. All structural calculations for permitted construction must be reviewed and stamped by a licensed structural engineer.