ASCE 7-22 · VELOCITY PRESSURE · q = 0.00256 V²
Wind Speed to Pressure Converter
Wind speed and wind pressure are two views of the same load. One equation ties them together: q = 0.00256 × V² — enter a speed in mph and read the velocity pressure in psf, or run it backward to recover the speed. It also converts psf, kPa, and Pa, so the number reads the same in any spec.
The base velocity pressure at standard conditions (all K-factors = 1.0). Site design pressure then layers on exposure, topography, directionality, and elevation.
THE CONVERSION
Speed and pressure, both ways
Velocity pressure is what a wind speed is, expressed as a load. The ASCE 7-22 relationship is a single equation you can run in either direction — speed to pressure, or pressure back to the speed that would produce it.
SPEED → PRESSURE
q = 0.00256 × V²
V in mph, q in psf. So 140 mph gives 0.00256 × 140² ≈ 50.2 psf, and 170 mph gives ≈ 74.0 psf — the base velocity pressure at standard conditions.
PRESSURE → SPEED
V = √( q ÷ 0.00256 )
Run it backward to see what speed a pressure implies. A 40 psf base velocity pressure corresponds to √(40÷0.00256) ≈ 125 mph.
V
The basic wind speed in mph — the 3-second gust from the ASCE 7-22 map, or a speed you're testing.
q
The velocity pressure in psf — what that speed pushes with, before any building factors.
0.00256
The fixed constant — half the density of air plus the mph-to-psf unit bundle. ASCE 7-22 Eq. 26.10-1.
V²
The square law — pressure rises with the square of speed, so small speed changes move q a lot.
psf · kPa
Read q in any unit — 1 psf = 47.88 Pa = 0.04788 kPa; 1 kPa = 20.885 psf.
This is the base velocity pressure at standard conditions. The full site pressure multiplies it by exposure (Kz), topography (Kzt), directionality (Kd), and elevation (Ke) — see the wind load pressure method.
THE SQUARE LAW
Why a little more speed is a lot more load
Because the V is squared, wind pressure climbs far faster than wind speed. That single fact is why a coastal upgrade from 140 to 170 mph is a bigger deal than it sounds, and why speeds are handled carefully.
Double the speed, 4× the load
Twice the mph is four times the psf. From 90 to 180 mph the base velocity pressure jumps from about 20.7 to 82.9 psf.
V²+10% speed, +21% pressure
A ten percent speed increase multiplies the pressure by 1.1² = 1.21. Small map revisions move real loads.
1.1²Round the speed up to 5
Design wind speeds are taken in 5-mph steps, rounded up — 138 mph becomes 140 — so the pressure is never understated.
5 MPHEvery psf here is the base velocity pressure at standard conditions. To turn a mapped speed into a site design pressure, layer on the K-factors and the shape coefficients — see the wind load pressure method.
UNITS
The same load, any unit
US drawings read in psf; metric and international specs read in kPa or Pa. It's one pressure — only the label changes. These factors move it cleanly in either direction.
psf
Pounds per square foot — the US customary unit for wind pressure and the one the DP ratings use.
1 psf = 47.88 PakPa
Kilopascals — the metric unit on international and SI drawings. About twenty-one psf to the kPa.
1 kPa = 20.885 psfPa
Pascals — newtons per square metre, for fine-grained work. A thousand Pa make one kPa.
1 psf = 0.04788 kPaBASE PRESSURE VS. SITE PRESSURE
This is the start, not the finish
q = 0.00256 V² is the base velocity pressure — it assumes flat open terrain, no hill, and sea level. A real site changes it. Exposure Kz accounts for terrain and height, Kzt for hills and escarpments, Kd for wind directionality, and Ke for ground elevation. Multiply them in and you have qz, the site velocity pressure; apply the shape coefficients and you have the design pressure a surface must resist. Use this converter to sanity-check the speed, then run the full method for the number that goes on the drawing.
FROM SPEED TO A REAL NUMBER
Ready for the site pressure?
The converter shows what a speed is worth in psf. When you need the actual design pressure for a wall, a roof, or an opening — with your ZIP's speed, exposure, and shape coefficients already applied — the free calculators do it end to end and return the number in about a minute. Full projects and an Engineering Report are on the paid tools.
Need the whole building, roofs, or specialty structures? See all calculators & pricing →
COMMON QUESTIONS
Speed and pressure, answered
What's the wind speed to pressure formula?
The velocity pressure is q = 0.00256 × V², with V in mph and q in psf. It's the ASCE 7-22 velocity pressure at standard conditions, before the exposure, topographic, directionality, and elevation factors. To reverse it, V = √(q ÷ 0.00256).
Why is the constant 0.00256?
It bundles half the mass density of air at standard conditions with the unit conversions that let you enter V in miles per hour and read q directly in pounds per square foot. It is the fixed coefficient in ASCE 7-22 Equation 26.10-1 for US customary units.
How do I convert psf to kPa or Pa?
One psf equals 47.88 pascals, which is 0.04788 kilopascals; one kilopascal equals 20.885 psf. So 40 psf is about 1.92 kPa, and 1 kPa is about 20.9 psf.
Does a higher wind speed mean much higher pressure?
Yes — pressure grows with the square of the speed, so doubling the speed quadruples the pressure and a 10% speed increase raises it about 21%. That's why going from 140 to 170 mph adds far more load than the speed change suggests. See the full pressure method.
KEEP READING
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