What is the difference between SS and SDS?

SS is the mapped MCER spectral acceleration at short period (0.2 s). SDS is the design short-period spectral acceleration at the site, computed as SDS = (2/3) × Fa × SS.

Where do I get Fa and Fv?

Fa and Fv are site coefficients from ASCE 7-22 tables based on Site Class and hazard values. The ASCE Hazard Tool can provide them when you specify Site Class.

Does Risk Category change SDS or SD1?

Risk Category affects certain limits and Seismic Design Category determination, but SDS and SD1 calculations themselves depend on SS, S1, Fa and Fv, not directly on Risk Category.

What units should I use?

Use g-units for SS, S1, SMS, SM1, SDS, and SD1 (dimensionless multipliers of gravitational acceleration).

Can I use Site Class F?

Yes, but Site Class F requires site-specific response analysis per ASCE 7-22; Fa and Fv are not tabulated and must be determined by analysis.

Is this calculator valid for ASCE 7-16?

Formulas are consistent across ASCE 7-16 and 7-22 for SDS and SD1. However, always verify coefficients and any local amendments.

ASCE 7-22 Seismic Design Calculator

This professional tool computes the ASCE 7-22 design spectral accelerations SDS and SD1 from mapped MCER hazard values (SS, S1) and site coefficients (Fa, Fv). It’s tailored for structural and civil engineers who need fast, accurate, and standards-compliant inputs for seismic design and documentation.

Calculator

Project name (optional)

Site Class *

Mapped MCER SS (g) *

Mapped MCER S1 (g) *

Site Coefficient Fa *

Site Coefficient Fv *

Need inputs? Open the official ASCE Hazard Tool in a new tab: ascehazardtool.org

Results

Enter valid inputs to see computed values. All results are in g-units.

SMS = Fa × SS —

SM1 = Fv × S1 —

SDS = (2/3) × SMS —

SD1 = (2/3) × SM1 —

Data Source and Methodology

Authoritative Data Source: American Society of Civil Engineers (ASCE), Minimum Design Loads and Associated Criteria for Buildings and Other Structures, ASCE/SEI 7-22 (2022). Official resource: ASCE/SEI 7-22. All calculations strictly follow the equations and definitions presented in Chapter 11 and Chapter 12 of ASCE 7-22.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

Mapped MCER spectral accelerations (SS, S1) and optional site coefficients (Fa, Fv) should be obtained from the official ASCE Hazard Tool.
The calculator applies the standard relationships to derive SMS, SM1, SDS, and SD1.

The Formula Explained

MCER spectral accelerations at the site:

$$ S_{MS} = F_a \cdot S_S \quad\text{and}\quad S_{M1} = F_v \cdot S_1 $$

Design spectral accelerations (two-thirds of MCER):

$$ S_{DS} = \tfrac{2}{3}\, S_{MS} \quad\text{and}\quad S_{D1} = \tfrac{2}{3}\, S_{M1} $$

Symbols are unitless (g-units). These equations are consistent with ASCE 7-22 Chapter 11.

Glossary of Variables

Site Class (A–F): Soil/rock category per ASCE 7-22 Chapter 20 determined from a geotechnical report.
SS (g): Mapped MCER spectral acceleration at 0.2 s from hazard maps/tools.
S1 (g): Mapped MCER spectral acceleration at 1.0 s from hazard maps/tools.
Fa (–): Short-period site coefficient from ASCE 7-22 tables (or analysis for Site Class F).
Fv (–): 1-second site coefficient from ASCE 7-22 tables (or analysis for Site Class F).
SMS (g): MCER short-period spectral acceleration at the site, SMS = Fa × SS.
SM1 (g): MCER 1-second spectral acceleration at the site, SM1 = Fv × S1.
SDS (g): Design short-period spectral acceleration, SDS = (2/3) × SMS.
SD1 (g): Design 1-second spectral acceleration, SD1 = (2/3) × SM1.

How It Works: A Step-by-Step Example

Suppose a project with Site Class D has the following hazard values from the ASCE Hazard Tool: SS = 1.50 g, S1 = 0.60 g. From ASCE 7-22 tables (for Site Class D), assume Fa = 0.90 and Fv = 1.50.

Compute MCER site values:
$$ S_{MS} = F_a \cdot S_S = 0.90 \times 1.50 = 1.350\ \text{g} $$

$$ S_{M1} = F_v \cdot S_1 = 1.50 \times 0.60 = 0.900\ \text{g} $$
Compute design spectral accelerations (two-thirds):
$$ S_{DS} = \tfrac{2}{3}\, S_{MS} = \tfrac{2}{3} \times 1.350 = 0.900\ \text{g} $$

$$ S_{D1} = \tfrac{2}{3}\, S_{M1} = \tfrac{2}{3} \times 0.900 = 0.600\ \text{g} $$

These SDS and SD1 values then feed into subsequent seismic design checks per ASCE 7-22 Chapter 12.

Frequently Asked Questions (FAQ)

How accurate are the results?

Results are exact with respect to the ASCE 7-22 equations. Ensure that SS, S1, Fa, and Fv are sourced from the official hazard tool or code tables to maintain accuracy.

Do I need a geotechnical report?

Yes, in most projects. The Site Class is a geotechnical parameter. Using the wrong Site Class may produce non-conservative results.

What precision should I report?

Many practitioners report to three decimals in g. Always conform to local practice and authority requirements.

Can I input PGA or TL?

This calculator focuses on SDS and SD1. PGA and TL can be important for other checks but are outside the current scope.

Why do my Fa and Fv differ from a colleague’s?

Fa and Fv depend on both Site Class and the mapped values SS and S1. If those inputs differ (or if a different edition or local amendment is used), coefficients will differ.

Does the tool determine Seismic Design Category (SDC)?

No. SDC determination also depends on Risk Category and other tables in ASCE 7-22. Use SDS, SD1 here as inputs to the relevant SDC tables.

Tool developed by Ugo Candido. Content reviewed by the CalcDomain Engineering Editorial Board.
Last reviewed for accuracy on: September 14, 2025.