Wind Load Calculator
Enter your wind speed, building dimensions, and site conditions to instantly calculate design wind pressure and total wind force on a structure. The calculator follows the ASCE 7 simplified procedure, applying the velocity pressure formula, a velocity pressure exposure coefficient (Kz) for the terrain and height, a gust factor, and an external pressure coefficient. Switch between metric (m/s, Pa) and imperial (mph, psf) units at any time.
Formula
Worked example
A 30 ft-tall building, 40 ft wide, 60 ft deep in Exposure C with a 115 mph design wind speed: Kz = 0.98, qz = 0.00256 x 0.98 x 0.85 x 115^2 = 31.7 psf. Windward p = 31.7 x 0.85 x 0.8 = 21.6 psf. L/B = 1.5 so Cp (leeward) = -0.4, leeward p = 31.7 x 0.85 x 0.4 = 10.8 psf. Net = 32.4 psf. Windward force = 21.6 x (30 x 40) = 25,920 lbf.
What is wind load and why does it matter?
Wind load is the force per unit area that wind exerts on a structure as it flows past. Any surface exposed to moving air experiences a pressure: a positive pressure on the windward face (wind pushing in) and a suction (negative pressure) on the leeward face and side walls (air accelerating around the building pulling outward). Both must be designed for. Wind load governs the sizing of lateral force-resisting systems such as shear walls, moment frames, and cross bracing, and it sets the uplift forces on roof connections. Underestimating it is one of the most common causes of structural failure in storms.
How the ASCE 7 wind load formula works
This calculator uses the ASCE 7 simplified procedure. The chain of calculation has five steps. First, the basic velocity pressure is computed as qz = 0.00256 × Kz × Kd × V², where V is the design wind speed in mph and the constant 0.00256 embeds standard air density at sea level. Second, the velocity pressure exposure coefficient Kz adjusts for terrain roughness and height: open coastal sites (Exposure D) have Kz near 1.0 at low heights, while sheltered suburban sites (Exposure B) start around 0.57. Third, the directionality factor Kd = 0.85 for buildings accounts for the reduced probability that the peak wind hits from the worst direction. Fourth, the design pressure on each wall is p = qz × G × Cp, where G = 0.85 is the gust factor for rigid structures and Cp is the external pressure coefficient (+0.8 windward, negative leeward depending on depth-to-width ratio). Fifth, the net force is F = p × A over the exposed area. The leeward Cp ranges from -0.5 (square plan) to -0.2 (deep plan), so both the depth and width of the building affect the total lateral demand.
Metric and imperial unit conversions
The ASCE 7 formula is written in US customary units (mph, ft, psf). When metric mode is selected, wind speed is converted from m/s to mph for the calculation, heights are converted from m to ft for Kz interpolation, and the resulting pressures are converted from psf to Pascals (1 psf = 47.88 Pa) and forces from lbf to Newtons (1 lbf = 4.448 N). Air density defaults to 1.225 kg/m^3 at sea level; for sites above roughly 1000 m the density drops meaningfully and the input can be adjusted. At 1600 m altitude (Denver, Colorado) the density is about 1.045 kg/m^3, reducing wind pressure by about 15 percent compared to sea level.
Components and cladding vs. main wind-force resisting system
The pressures this calculator gives apply to the Main Wind-Force Resisting System (MWFRS), the structural skeleton that transfers lateral loads to the foundation. Component and cladding (C&C) pressures for windows, wall panels, roof sheathing, and fasteners are different and are generally larger in magnitude, particularly at building corners and roof edges. ASCE 7 Chapter 30 covers C&C and requires separate calculations using effective wind area and zone-specific pressure coefficients. Always consult the relevant chapter of ASCE 7 (or the applicable building code in your jurisdiction) and a licensed structural engineer for final design.
ASCE 7 Exposure Category Kz values (selected heights)
| Height (ft) | Exposure B | Exposure C | Exposure D |
|---|---|---|---|
| 15 | 0.57 | 0.85 | 1.03 |
| 20 | 0.62 | 0.9 | 1.08 |
| 30 | 0.7 | 0.98 | 1.16 |
| 40 | 0.76 | 1.04 | 1.22 |
| 50 | 0.81 | 1.09 | 1.27 |
| 60 | 0.85 | 1.13 | 1.31 |
| 80 | 0.93 | 1.21 | 1.38 |
| 100 | 0.99 | 1.26 | 1.43 |
| 120 | 1.04 | 1.31 | 1.48 |
| 160 | 1.13 | 1.39 | 1.55 |
| 200 | 1.2 | 1.46 | 1.61 |
Velocity pressure exposure coefficient Kz from ASCE 7-16 Table 26.10-1. Higher values = greater wind exposure.
Frequently asked questions
What is the ASCE 7 wind load formula?
The core formula is qz = 0.00256 x Kz x Kd x V^2 for velocity pressure (psf), where V is the 3-second gust design wind speed in mph. Design pressure on a wall is then p = qz x G x Cp, where G is the gust factor (0.85 for rigid buildings) and Cp is the external pressure coefficient (+0.8 on the windward wall). Total force is F = p x A.
What is the difference between Exposure B, C, and D?
Exposure Category B applies to urban and suburban areas, wooded areas, and other terrain with numerous closely spaced obstructions. Exposure C covers open terrain with scattered obstructions generally less than 30 ft high. Exposure D is the most severe, applying to flat, unobstructed coastal areas, mudflats, salt flats, and shorelines. The category is selected based on the fetch (upwind terrain) in the direction from which the critical wind comes, for a distance of at least 1500 ft (Exp. B) or 5000 ft (Exp. C/D).
What design wind speed should I use?
ASCE 7 provides wind speed maps by geographic location and risk category. For most standard-occupancy buildings (Risk Category II) in the continental US, design speeds range from about 85 mph in the interior to 170 mph or more along exposed Gulf and Atlantic coastal areas. Use the applicable map in ASCE 7-22 (or whichever edition your local building code has adopted), or check with your local building department for the adopted code and site-specific requirements.
How do I convert wind speed to pressure (psf or Pa)?
The simplified relationship is q = 0.00256 x V^2 (psf) for standard sea-level conditions, where V is in mph. In metric terms, q = 0.5 x rho x V^2 (Pa) where rho is air density (1.225 kg/m^3 at sea level) and V is in m/s. For example, a 100 mph wind gives about 25.6 psf of basic velocity pressure; at 45 m/s the pressure is about 1,239 Pa. Both figures exclude Kz, Kd, and pressure coefficients.
Does wind speed affect pressure linearly or quadratically?
Quadratically. Wind pressure is proportional to the square of wind speed. Doubling the wind speed increases the pressure by a factor of four, not two. This is why hurricane-force winds cause dramatically more damage than gale-force winds even though the speed difference may seem moderate.
What is the gust factor and when does it change?
The gust factor G accounts for the dynamic amplification of wind gusts on the structure. ASCE 7 permits G = 0.85 for rigid structures, defined as those with a fundamental natural frequency of 1 Hz or greater (typically low-rise and mid-rise buildings with stiff lateral systems). Tall, slender, or flexible structures require a calculated gust factor Gf per ASCE 7 Section 26.11.4, which can exceed 1.0 and significantly increase design loads.
What is the leeward pressure coefficient and how does depth-to-width ratio affect it?
The leeward Cp is always negative (suction). ASCE 7 sets it at -0.5 for buildings where the depth equals the width (L/B = 1), -0.3 for L/B = 2, and -0.2 for L/B = 4 or more. This means a shallow building (square plan) has more leeward suction per unit area than a deep one. The calculator interpolates Cp linearly between these values.
How does altitude affect wind load?
Air density decreases with altitude, which reduces dynamic pressure and wind force. At sea level the density is about 1.225 kg/m^3; at 1500 m it is roughly 1.058 kg/m^3 (a 14 percent reduction); at 3000 m it is about 0.909 kg/m^3 (a 26 percent reduction). The ASCE 7 constant 0.00256 assumes sea-level density. Adjust the air density input in this calculator for high-altitude sites, or consult the local building code, which may specify a modified wind speed or pressure for the elevation.