Wind Pressure Calculator
Wind psf, roof uplift, and hurricane category.
What it does
Wind pushes with the square of its speed. One hundred mph presses 25.6 psf while 157 mph presses 63.1, so Category 5 more than doubles Category 2 pressure. Roofs feel the product: pressure times area lifts thousands of pounds.
The tool above runs base ASCE 7 velocity pressure with K factors at 1. Enter mph and roof square feet for psf, uplift pounds, and the Saffir-Simpson category. Defaults give 25.6 psf with 25,600 lb on 1,000 sq ft at Category 2.
Standards confirm each piece. ASCE 7 carries the qz equation with 0.00256 from air density through unit conversion, and NOAA publishes the Saffir-Simpson bands from tropical storm through Category 5. Full design adds exposure, height, gust, and shape factors.
Uplift decides connections before sheathing. Straps, clips, and anchors must beat the computed pounds with margins, since gusts punch past sustained figures. Evacuation and shutter calls follow forecasts, not this page.
How to use
- Enter the wind speed in mph.
- Enter the roof area in sq ft.
- Read psf first, then uplift.
- Read the hurricane category.
- Apply K factors for real design.
- Anchor roofs for the uplift.
Formula
- V
- Sustained wind speed in mph, 0 to 300.
- roof
- Roof area catching uplift in sq ft.
ASCE 7 Eq. 26.10-1 with K=1; NOAA confirms Saffir-Simpson bands. Full design needs exposure and gust factors.
Worked example
Example: 100 mph wind
Defaults: 100 mph on 1,000 sq ft.
- Inputs: 100 mph wind, 1,000 sq ft roof.
- Square: 100 x 100 = 10,000.
- Pressure: 0.00256 x 10,000 = 25.6 psf.
- Uplift: 25.6 x 1,000 = 25,600 lb.
- Category 2 (96-110 band edge check: 100 sits inside). Tool shows 25.6 psf, 25,600 lb.
Reference table
| Wind | psf | Category |
|---|---|---|
| 74 mph | 14.02 | Cat 1 low |
| 95 mph | 23.10 | Cat 1 high |
| 100 mph | 25.60 | Cat 2 |
| 129 mph | 42.60 | Cat 3 high |
| 157 mph | 63.10 | Cat 5 low |
Limits
- Base pressure only (K=1). Real design differs.
- Sustained winds; gusts punch higher.
- Shape and opening effects excluded.
- Not a structural design stamp.
Common mistakes
- Reading mph as psf directly.
- Forgetting uplift multiplies by area.
- Ignoring gust factors in design.
- Mixing 3-sec gusts with sustained bands.
- Skipping professional stamps.
Try it yourself
Quick checks. Answers sit tucked under each question.
90 mph on 1,500 sq ft?
90^2 = 8,100. q = 0.00256 x 8,100 = 20.74 psf. Uplift 20.74 x 1,500 = 31,104 lb. Cat 1.
157 mph on 1,800 sq ft?
157^2 = 24,649. q = 63.1 psf. Uplift 63.1 x 1,800 = 113,583 lb. Cat 5.
Questions
How is wind pressure figured?
0.00256 times mph squared (K factors = 1). Here 0.00256 x 10,000 = 25.6 psf.
How is uplift figured?
Pressure times roof area. Here 25.6 x 1,000 = 25,600 lb of uplift.
What are the hurricane bands?
Cat 1: 74-95, Cat 2: 96-110, Cat 3: 111-129, Cat 4: 130-156, Cat 5: 157+ mph.
Where does 0.00256 come from?
Yes: 0.5 x 0.002378 air density times the mph-to-ft/s conversion squared gives 0.00256.
Is this the full ASCE 7?
Yes. Exposures, gusts, heights, and shapes need full ASCE 7 tables with K factors.
Do weak storms matter?
Yes. Tropical storm under 74 mph still damages; categories start at 74.