Wind Load Calculator
Calculate wind velocity pressure using the ASCE 7 formula from basic wind speed and exposure factors — a simplified version of the code's wind load calculation.
How this calculator works
Wind pushes on a building because moving air carries force, and that force has to be turned into a number before anyone can size a wall, roof, or connection against it. ASCE 7 starts that process with a value called velocity pressure — how hard the wind pushes based purely on its speed, before accounting for the building’s shape.
This calculator runs that first step. You enter the basic wind speed for your site along with three adjustment factors, and it returns the velocity pressure in pounds per square foot (psf).
Formula: qz = 0.00256 × Kz × Kzt × Kd × V², where V is basic wind speed in mph, Kz is the exposure coefficient (height/terrain-dependent), Kzt is the topographic factor, and Kd is the wind directionality factor.
Worked example
A site with basic wind speed V = 115 mph, Kz = 1.0, Kzt = 1.0, and Kd = 0.85 (standard for buildings):
- qz = 0.00256 × 1.0 × 1.0 × 0.85 × 115²
- 115² = 13,225
- qz = 0.00256 × 0.85 × 13,225 ≈ 28.78 psf
Notes
This is the velocity pressure step of ASCE 7’s wind load procedure. The full calculation then multiplies qz by a pressure coefficient (GCp) that depends on the building’s shape and which surface — wall, roof, or corner — you’re checking. That coefficient varies by geometry, so it isn’t a single number this calculator can supply.
Basic wind speed (V) comes from the ASCE 7 wind speed map for your location, not from a formula. Look it up for your address before using this calculator, since an incorrect V changes the result by the square of the error.
How to use
Enter the basic wind speed for your site, along with the exposure, topographic, and directionality factors that apply to your building. The calculator returns velocity pressure (qz) in psf — the base value the full ASCE 7 wind load procedure builds on for a specific surface.
This is a planning estimate using a simplified version of the standard code formula, not a substitute for engineering design. Confirm actual load values and code compliance with a licensed structural engineer.
Frequently asked questions
What is velocity pressure (qz) and why isn't it the final wind load?
Velocity pressure is the base pressure the wind's speed alone creates against a surface. It's the first step in the ASCE 7 procedure, not the final design wind load — the code then multiplies qz by a pressure coefficient specific to the building's shape and the surface being checked, so qz on its own understates the real force on any one wall, roof plane, or corner.
Where do I find the basic wind speed (V) for my location?
Basic wind speed comes from the ASCE 7 wind speed map, which assigns a design speed in mph to your location based on historical storm data. It is not something you calculate — look it up for your address in the current ASCE 7 map or ask your local building department, then enter that value here.
What do Kz, Kzt, and Kd represent?
Kz is the exposure coefficient, adjusting for building height and surrounding terrain roughness. Kzt is the topographic factor, adjusting for hills or ridges that speed up wind. Kd is the wind directionality factor, a code-specified reduction (0.85 for most buildings) accounting for the odds of peak wind hitting the worst-case direction and surface at once.
Can I use this qz value to size a beam, wall, or connection?
No. Velocity pressure is only an intermediate step toward the full wind load procedure in ASCE 7, which also requires the correct pressure coefficient (GCp) for the specific surface and building geometry involved. Member sizing and connection design are safety-critical and must be completed by a licensed structural engineer.
Estimates only. Verify quantities with your supplier before purchasing.