Seismic Base Shear Calculator

About this calculator

The equivalent lateral force procedure, the standard simplified method in seismic design codes like ASCE 7, models earthquake shaking as a single static horizontal force applied at the building's base: V = C_s · W, where W is the building's seismic weight and the seismic response coefficient C_s = S_DS / (R/I_e) is built from the design spectral acceleration S_DS, the structural system's response modification factor R, and the occupancy importance factor I_e.

This calculator computes that base shear directly from your four inputs. Structural and civil engineers use it during preliminary seismic design to size a building's lateral force-resisting system, building code plan reviewers use the same formula to check submitted calculations for code compliance, and seismic retrofit consultants use it to compare an existing structure's capacity against the demand a current code would require.