What this calculator does
Wind pressure is a velocity pressure multiplied by a shape coefficient, and the two come from different places. The site fixes the first; what the surface actually IS fixes the second. A parapet edge and a flat wall differ by a factor of several, and that choice is the whole design task.
How to use it
- Enter the reference wind velocity for your site and the exposure/height factor for this building.
- Enter the shape coefficient for the SURFACE you are checking — the tool will not choose one for you.
- Enter the area and the force coefficient for the particular force you need.
- Note that uplift is NOT covered here: wind suction on a roof is comparable to the downward pressure.
Governing formula
q_p = ½ · ρ · v² · c_e → p = q_p · c_pe → F = p · A · C_f Where:
-
q_p= Velocity pressure, Pa -
c_e= Exposure / height factor -
c_pe= Shape coefficient for the surface -
C_f= Force coefficient
Derived Equations:
q ∝ v² Worked example — 30 m/s on a 25 m² wall
The figures below were produced by running this page's own engine with the example inputs (Reference wind velocity (m/s), Air density (kg/m³), Exposure / height factor (–), Shape coefficient for this surface (–), Surface area (m²), Force coefficient (–)). If the calculator returns something different for the same numbers, that is a bug, not a rounding difference.
| Total force on the surface | 21499 N |
|---|---|
| Pressure on the surface | 661.5 Pa |
| Site velocity pressure | 826.88 Pa |
| Force per m² | 859.95 N/m² |
| What this means | The site velocity pressure is 827 Pa. With a shape coefficient of 0.8 the surface sees 662 Pa, and the force on 25 m² is 21.50 kN. |
- The velocity pressure is ½ · 1.225 · 30² · 1.5 ≈ 827 Pa.
- At c_pe = 0.8 the surface sees about 662 Pa.
- Over 25 m² with C_f = 1.3 that is roughly 21.5 kN.
Assumptions & limitations
Engineering calculation. Velocity pressure from the site, then the surface pressure and force for a shape coefficient YOU supply for the surface in question.
- The shape coefficient is YOUR value for the surface. This tool holds no pressure-coefficient table and does not choose one for a wall, a roof zone or a parapet — that choice is the whole design task.
- Velocity, density and the exposure/height factor are site inputs. No code edition, terrain roughness, gust factor, reference height or standard is asserted here.
- Suction is not modelled. Wind uplift on a roof is comparable to the downward pressure and is NOT represented by this tool, which reports pressure and force only.
- No internal pressure, netting, porosity, shielding between buildings, dynamic response or vortex shedding is included.
This tool supports professional engineering work; it does not replace a sealed design. Confirm every result against the applicable standard and a licensed engineer before it is built.
References & standards
- BS EN 1991-1-4 and ASCE/SEI 7 — wind actions, as the framework behind the coefficients.