Wind Load Calculator (ASCE 7)
Simplified wind pressure in psf and force in lb from wind speed, height, exposure and risk category, in the style of ASCE 7. Not a design calculation. How it works
Use the Wind Load Calculator (ASCE 7)
About the Wind Load Calculator (ASCE 7)
At 115 mph, 30 ft, Exposure C, Risk Category II, an enclosed building and Kzt 1.0, this simplified estimate gives a velocity pressure of 28.27 psf and a main wind force pressure of 24.31 psf. It follows the shape of the ASCE 7 equation q = 0.00256 × Kz × Kzt × Kd × V² × I with fixed coefficients, so it is an orientation figure, not an ASCE 7-22 calculation and not a design value.
Velocity pressure and MWFRS pressure by wind speed
| Wind speed | Velocity pressure q | MWFRS pressure p |
|---|---|---|
| 85 mph | 15.44 psf | 13.28 psf |
| 100 mph | 21.37 psf | 18.38 psf |
| 115 mph | 28.27 psf | 24.31 psf |
| 130 mph | 36.12 psf | 31.06 psf |
| 150 mph | 48.09 psf | 41.36 psf |
| 180 mph | 69.25 psf | 59.56 psf |
At 30 ft, Exposure C, Risk Category II, enclosed, Kzt 1.0. Pressure grows with the square of the speed: 200 mph gives four times the pressure of 100 mph.
Velocity pressure coefficient Kz by height and exposure
| Height | Exposure B | Exposure C | Exposure D |
|---|---|---|---|
| 15 ft | 0.575 | 0.849 | 1.030 |
| 30 ft | 0.701 | 0.982 | 1.162 |
| 60 ft | 0.854 | 1.137 | 1.311 |
| 100 ft | 0.988 | 1.266 | 1.433 |
| 200 ft | 1.205 | 1.464 | 1.616 |
| 500 ft | 1.565 | 1.776 | 1.896 |
Kz = 2.01 × (z / zg)^(2 / α), with zg 1,200, 900 and 700 ft and α 7.0, 9.5 and 11.5 for B, C and D, and z at least 15 ft.
Components & Cladding pressure by roof zone, 10 sq ft element
| Roof zone | GCp used | Design pressure p | Element force |
|---|---|---|---|
| Interior | -0.9 | -30.53 psf | -305.28 lb |
| Edge | -1.2 | -39.01 psf | -390.08 lb |
| Corner | -1.8 | -55.97 psf | -559.68 lb |
Same inputs as the example. The page shows the governing negative value, which is suction. The roof-zone coefficients are illustrative values set by this page, not read from the ASCE 7 figures, so edge and corner suction may be understated.
Assumptions
- Importance factors 0.87, 1.00, 1.15 and 1.15 for risk categories I to IV. The American Wood Council comparison gives 1.0 for Category II and 1.15 for III and IV under ASCE 7-05; the 0.87 for Category I is not verified.
- Components and cladding use the negative coefficients −0.9, −1.2 and −1.8 for interior, edge and corner zones, with no reduction for effective wind area.
How to use this tool
- Choose MWFRS (main wind force system) or Components & Cladding.
- Type the wind speed (85 to 250 mph), the building height (15 to 500 ft), the exposure (B, C or D), the risk category (I to IV), the enclosure class and Kzt (1.00 to 3.00).
- For MWFRS add a wall width in ft; for Components & Cladding add an element area in sq ft and a roof zone.
- Read the velocity pressure q, the design pressure p (negative is suction) and the force. Open Calculation Methodology to see each step.
Frequently asked questions
- How do you calculate wind load in psf?
- Start from the velocity pressure q = 0.00256 × Kz × Kzt × Kd × V², with V in mph, then multiply by a pressure coefficient and add or subtract the internal pressure. At 115 mph, 30 ft and Exposure C, q is 28.27 psf. This page uses a gust factor of 0.85 and a windward coefficient of 0.8, giving 24.31 psf for the main wind force system.
- Does this calculator follow ASCE 7-22?
- No. It is a simplified estimate in the style of ASCE 7. It uses a fixed directionality factor of 0.85, a fixed gust factor of 0.85, one windward coefficient of 0.8, its own components and cladding coefficients by roof zone, and internal pressure of ±0.18 (enclosed) or ±0.55 (partially enclosed). A licensed structural engineer must do the design.
- Which wind speed and risk category should I enter?
- Here the category only sets an importance factor of 0.87, 1.00, 1.15 or 1.15, so Risk Category III gives 32.51 psf against 28.27 psf for II at the starting values. Since ASCE 7-10 the standard has no such factor: it gives a separate basic wind speed map for each risk category instead. If you read V from the map for your building’s category, choose Risk Category II here so the factor is not counted twice.
- What do Exposure B, C and D mean?
- They describe the ground the wind crosses before it reaches the building. The American Wood Council summarizes ASCE 7-10 as: B, urban and suburban areas, wooded areas or other terrain with many closely spaced obstructions; C, open terrain with scattered obstructions; D, flat, unobstructed areas facing wind over open water for at least a mile. At 30 ft this page’s Kz is 0.701, 0.982 and 1.162 for B, C and D, so the same wind gives about two-thirds more pressure in D than in B.
- How close is Kz to the ASCE 7 values?
- A comparison published by the American Wood Council for ASCE 7-10 lists Kz of 1.0 for Exposure C and 1.18 for Exposure D at 33 ft, and 1.13 (C) and 1.31 (D) at 60 ft. This page gives 1.002, 1.182, 1.137 and 1.311 for those cases.
- Why is the pressure negative?
- A negative value is suction, pulling away from the surface. The components and cladding mode uses the negative coefficient for the roof zone you pick, so a corner element at the starting values gets -55.97 psf, and a 10 sq ft element -559.68 lb. The page takes the internal-pressure sign that gives the larger magnitude.
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