Which ASCE 7-22 formula does this calculator use for velocity pressure?

It uses qz = 0.00256 Kz Kzt Kd V^2 I with V in mph, as provided in ASCE 7-22 Chapter 26.

How are exposure categories handled?

Kz is computed with the power-law expression using zg and α for Exposure B, C, or D as specified in ASCE 7-22 Table 26.10-1.

Does the tool support internal pressure (GCpi)?

Yes. You can choose Enclosed (±0.18), Partially Enclosed (±0.55), Open (0.0), or specify a custom GCpi.

What is the default gust effect factor G?

For rigid buildings, G typically defaults to 0.85. You can override this if a dynamic analysis indicates a different value.

Are the outputs strength-level or ASD-level?

The pressures are strength-level per ASCE 7-22 unless you post-process per your load combinations. Apply appropriate factors for ASD if needed.

Where do I get the correct basic wind speed?

Use the official ASCE Hazard Tool (https://ascehazardtool.org) for your site coordinates and risk category.

ASCE 7-22 Wind Load Calculator (Main Wind-Force Resisting System)

This professional-grade calculator helps structural and civil engineers compute ASCE 7-22 wind loads for Main Wind-Force Resisting Systems (MWFRS). It streamlines velocity pressure and design pressure calculations with full control over exposure, height, risk category, and coefficients—optimizing accuracy, accessibility, and speed.

Calculator

Basic wind speed V (3-sec gust) *

mph

Exposure category *

Risk category *

I = 1.00

Mean roof height h *

Evaluate at h Custom z

Directionality factor Kd *

—

Topographic factor Kzt *

—

Gust effect factor G *

—

External pressure coefficient Cp

—

Enclosed (±0.18) Partially Enclosed (±0.55) Open (0.0) Custom GCpi

—

The calculator envelopes both GCpi signs when applicable.

Results

Importance factor I 1.00

G × Cp 0.68

Kz at z —

Kz at h —

qz (at z) —

qh (at h) —

Design p (GCpi +) —

Design p (GCpi −) —

Max pressure envelope —

Max suction envelope —

Data Source and Methodology

Authoritative data source: ASCE/SEI 7-22, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Chapters 26–30. Reference: American Society of Civil Engineers (ASCE), 2022.

Standard overview: ASCE/SEI 7-22
Official wind speed maps: ASCE Hazard Tool
Background guides: ASCE 7 Guides

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

The Formula Explained

Velocity pressure:

$$ q_z = 0.00256 \; K_z \, K_{zt} \, K_d \, V^2 \, I \quad [\mathrm{psf}] $$

Exposure coefficient (power law):

$$ K_z = 2.01 \left(\frac{z}{z_g}\right)^{\frac{2}{\alpha}}, \quad 15\,\mathrm{ft} \le z \le z_g $$

where for Exposure B: (z_g=1200\,ft, \alpha=7), Exposure C: (z_g=900\,ft, \alpha=9.5), Exposure D: (z_g=700\,ft, \alpha=11.5). Clamp z to [15 ft, z_g].

Design pressure (MWFRS, surface/zone):

$$ p = q_z \, G \, C_p \;-\; q_i \, (GC_{pi}), \quad \text{with } q_i \approx q_h $$

Glossary of Variables

V (mph): Basic 3-second gust wind speed from ASCE maps (ASCE Hazard Tool).
Exposure (B/C/D): Terrain roughness category affecting wind profile and Kz.
h (ft): Mean roof height. Use z = h for many MWFRS surfaces.
z (ft): Height where external pressure is evaluated. Clamped to ≥ 15 ft and ≤ z_g.
Kz: Exposure coefficient per ASCE 7-22 power-law expression.
Kzt: Topographic factor for speed-up; 1.0 if not applicable.
Kd: Directionality factor (typically 0.85 for buildings).
I: Importance factor for wind: 0.87 (Risk I), 1.0 (Risk II), 1.15 (Risk III/IV).
G: Gust effect factor; 0.85 for rigid buildings unless otherwise determined.
Cp: External pressure coefficient for the MWFRS surface/zone.
GCpi: Internal pressure coefficient including gust; depends on enclosure.
qz, qh (psf): Velocity pressures at height z and at mean roof height h.
p (psf): Design pressure. The tool reports both GCpi signs and envelopes the results.

How it Works: A Step-by-Step Example

Scenario. Single-story office, Exposure C, h = 30 ft, Risk Category II, V = 115 mph, Kd = 0.85, Kzt = 1.0, G = 0.85, Cp = +0.8 (windward wall), Enclosed (GCpi = ±0.18).

Compute Kz at h: For Exposure C, z_g = 900 ft, α = 9.5. Kz = 2.01 × (30/900)^(2/9.5) ≈ 0.72.
Velocity pressure at h: qh = 0.00256 × Kz × Kzt × Kd × V² × I = 0.00256 × 0.72 × 1.0 × 0.85 × 115² × 1.0 ≈ 32.8 psf.
External: G × Cp = 0.85 × 0.8 = 0.68. Internal: GCpi = ±0.18; take qi ≈ qh.
Design pressure: p(+) = qh × 0.68 − qh × (+0.18) = qh × 0.50 ≈ 16.4 psf; p(−) = qh × 0.68 − qh × (−0.18) = qh × 0.86 ≈ 28.2 psf.
Envelope: Maximum pressure ≈ +28.2 psf (toward the surface), Maximum suction ≈ −16.4 psf (away from the surface) if Cp negative; for windward Cp positive, suction may not govern for this surface.

Always use the correct Cp for the governed surface/zone and check all load cases per ASCE 7-22 Chapters 27 and 28.

Frequently Asked Questions (FAQ)

Which formula is used for velocity pressure?

qz = 0.00256 Kz Kzt Kd V² I, with V in mph, per ASCE 7-22 Chapter 26. Kz is computed using the exposure-specific power law.

Is qi always equal to qh?

For buildings, ASCE commonly takes internal velocity pressure qi at mean roof height. This tool sets qi = qh.

How do I select Cp?

Choose Cp from MWFRS figures in ASCE 7-22 (Ch. 27 & 28) for the specific surface, zone, and roof slope. Enter the sign as shown in the standard.

What about Components & Cladding (C&C)?

This tool targets MWFRS. C&C uses different coefficients and zones. Use a dedicated C&C calculator.

Does this tool account for topographic speed-up?

Yes—set Kzt per Chapter 26. If not applicable, use Kzt = 1.0.

Are outputs suitable for permit submittals?

They are based on ASCE 7-22 formulas. However, final design is the responsibility of a licensed professional verifying all assumptions and cases.

Can I use SI units?

This version uses U.S. customary units (mph, ft, psf). A future update may include SI support.

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