Wind Shear Exponent Calculator

1. Select a calculation mode matching your available data.
2. Enter heights and wind speeds using consistent units.
3. Optionally choose a terrain preset to suggest α.
4. Press Submit to view results above the form.
5. Use Download CSV or Download PDF to archive the run.

1) What the wind shear exponent represents

The wind shear exponent (α) describes how wind speed changes with height above ground. Lower values indicate smoother exposure such as open terrain, while higher values reflect rougher exposure with buildings and trees. In practical projects, α often falls around 0.10 to 0.33, but site conditions can vary.

2) Power-law method used in this calculator

This tool applies the power-law profile, V(z) = V_ref(z/z_ref)^α. When two measured points are available, α is derived from α = ln(V₂/V₁) / ln(z₂/z₁). Using logarithms stabilizes scaling and keeps α dimensionless.

3) Selecting reliable input data

Use averaged wind speeds over a consistent period (for example, 10-minute means) rather than momentary gusts. Choose heights with meaningful separation; a larger height ratio reduces sensitivity to measurement noise. Keep all heights in one unit system, and ensure both speeds are recorded under comparable weather conditions.

4) Example for elevated work and lifting operations

With V₁ = 8.5 m/s at z₁ = 10 m and V₂ = 11.2 m/s at z₂ = 50 m, the computed exponent is approximately α ≈ 0.171. If a target elevation is zᵗ = 80 m, the extrapolated wind speed becomes about 12.2 m/s. This supports preliminary checks for crane booms, temporary towers, and scaffold elevations.

5) Practical checks and limitations

The power-law approach is a simplified profile and does not replace site monitoring plans or governing standards. Complex terrain, nearby obstructions, strong stability effects, and storm events can alter the profile significantly. If α appears negative or unusually high, recheck sensors, heights, and data alignment.

1) Why did I get a negative α?

Negative α usually means the higher measurement is slower than the lower one, or heights were swapped. Confirm z₁, z₂, V₁, and V₂ are correct, positive, and represent the same averaging period.

2) Do speed units affect the exponent?

No. α is unitless because it uses a ratio of speeds. However, V₁, V₂, and V_ref must all be in the same unit for correct results.

3) Can I use feet for height inputs?

Yes. Heights can be in feet or meters as long as all height fields use the same unit. The exponent calculation depends on ratios, so consistent units are essential.

4) What does the terrain preset do?

Terrain presets provide a typical α value for an exposure type. They are useful when only one measured point is available. For critical work, prefer site-specific measurements or the controlling project standard.

5) Which mode should I choose?

Use “Compute α from two speeds” when you have two measured heights. Use “Compute speed at target height” when α is known or selected. Use “Compute α and speed at target” to do both in one run.

6) What is included in the CSV and PDF?

The CSV includes inputs, computed α, target-speed output, and a timestamp. The PDF is generated from the visible page values at download time, making it convenient for reporting and site records.

7) Is this suitable for lift go/no-go decisions?

Use it for planning and screening, not as the sole basis for safety-critical decisions. Follow the project lift plan, manufacturer limits, real-time monitoring, and the governing standard for your worksite.

Wind shear affects temporary works, crane operations, scaffold loading checks, and elevated work zones where wind speed increases with height.

Use this tool for planning and preliminary checks. For high-risk lifts or code-governed design, rely on site monitoring plans and the controlling standard for your project.