What this calculator does
Wind load is the force that moving air exerts on a surface, such as a sign, a fence panel or a flat wall section. A simplified but widely used way to estimate it is the basic drag-force formula: force equals half the air density, times wind speed squared, times a drag coefficient, times the exposed area.
This calculator uses that simplified formula, not a full building-code wind assessment. Standards such as AS1170 build in terrain category, building height, gust factors, importance factors and other variables this basic formula does not capture, so treat the result here as a rough estimate for learning or early sizing, not a substitute for a proper structural wind-load calculation on any real structure.
The formula
Wind speed is converted to metres per second, then squared, since drag force rises with the square of speed. This is multiplied by air density (about 1.225 kg per cubic metre at sea level), a drag coefficient describing how bluff or streamlined the shape is (around 1.2 for a flat plate face-on to the wind), and the area exposed to the wind, then halved.
| Term | Meaning |
|---|---|
| Air density (ρ) | Mass of air per cubic metre, roughly 1.225 kg/m³ at sea level and 15°C, lower at altitude or in hot air. |
| Drag coefficient (Cd) | A dimensionless number describing how much drag a shape produces; around 1.0 to 1.2 for a flat plate facing the wind, lower for streamlined shapes. |
| Exposed area (A) | The area of the surface facing into the wind, in square metres. |
| Wind load (F) | The resulting force on the surface, in newtons: F = 0.5 × ρ × v² × Cd × A. |
The inputs explained
| Field | What to enter |
|---|---|
| Wind speed (km/h) | Wind speed, in kilometres per hour, converted internally to metres per second for the formula. |
| Air density (kg/m³) | Air density; 1.225 kg/m³ is a common sea-level default, lower at altitude or in warmer air. |
| Drag coefficient | Drag coefficient for the shape; around 1.2 for a flat surface square to the wind. |
| Surface area exposed (m²) | Area of the surface exposed to the wind, in square metres. |
When to use it
Sizing a fence panel or hoarding
A quick estimate of the force a gust could put on a flat panel, before deciding whether bracing or a lower solid area is needed. Final sizing for anything load-bearing should still follow the relevant building code.
Sanity-checking a code calculation
A basic drag-force number gives a rough ballpark to compare against a more detailed AS1170 or equivalent standard-code result, as a check that the fuller calculation is in the right order of magnitude.
Teaching or coursework
The formula is a standard introductory fluid-dynamics relationship, useful for working through how force scales with wind speed and area.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How wind load changes with wind speed, on a fixed 2 m² surface
The same panel facing a range of wind speeds.
| Wind speed | Wind load (force) |
|---|---|
| 40 km/h | 181.5 N |
| 60 km/h | 408.3 N |
| 80 km/h | 725.9 N |
| 100 km/h | 1,134.3 N |
| 120 km/h | 1,633.3 N |
| 150 km/h | 2,552.1 N |
How wind load changes with exposed area, at 80 km/h
The same wind speed against panels of increasing area.
| Exposed area | Wind load (force) |
|---|---|
| 0.5 m² | 181.5 N |
| 1 m² | 363.0 N |
| 2 m² | 725.9 N |
| 4 m² | 1,451.9 N |
| 6 m² | 2,177.8 N |
| 10 m² | 3,629.6 N |
Questions
How do you calculate wind load?
Use F = 0.5 × air density × wind speed squared × drag coefficient × area, with wind speed in metres per second. This gives an estimate of the force in newtons on a flat surface.
What is the wind load formula in full?
F = 0.5 × ρ × v² × Cd × A, where ρ is air density, v is wind speed, Cd is the drag coefficient of the shape, and A is the exposed area.
Is this the same as an AS1170 wind load calculation?
No. AS1170 and similar building codes add terrain roughness, building height, regional wind speed data, gust and importance factors. This calculator only applies the basic drag formula and should not replace a code-compliant assessment for any structure people rely on.
What drag coefficient should I use?
Around 1.0 to 1.2 is typical for a flat surface facing directly into the wind. Rounder or more streamlined shapes have lower coefficients; the exact value depends on shape and orientation.
For everyday air-resistance style force calculations rather than structural sign-off, this pairs with the general physics tools; check local building code requirements such as AS1170 for anything load-bearing.