Learn: Basic wind velocity pressure
Basic velocity pressure converts a supplied basic wind speed into an energy-per-volume scale. It is a starting quantity for wind action calculations, not yet the pressure on a particular wall or roof.
What the formula is saying
The kinetic-energy expression contains one half of air density times speed squared. Squaring speed explains why a modest speed increase can produce a much larger pressure increase.
Read the symbols in plain language
- ρ
- Air density
Mass per unit volume for the stated material and condition. This is density, not weight per volume.
kg/m³Use kg/m³ as the base unit shown here. Use air density in kg/m³ and basic wind speed in m/s. The result is kg/(m·s²) = Pa. Convert km/h to m/s by dividing by 3.6 before squaring.
- vb
- Basic wind velocity
Basic wind velocity. Velocity pressure follows kinetic energy, which depends on speed squared.
m/sUse m/s as the base unit shown here. Use air density in kg/m³ and basic wind speed in m/s. The result is kg/(m·s²) = Pa. Convert km/h to m/s by dividing by 3.6 before squaring.
- qb
- Result to find
Basic wind velocity pressure. Multiply by half the air density to obtain pressure in pascals.
Pa
Sort out the units first
Use air density in kg/m³ and basic wind speed in m/s. The result is kg/(m·s²) = Pa. Convert km/h to m/s by dividing by 3.6 before squaring.
Assumptions before calculating
Air density and basic speed are supplied for the intended conditions. The speed is a magnitude, and the reference definition of basic speed must match the wind-action method being used.
This is a first-generation Eurocode teaching relationship or an explicitly simplified coefficient calculation. The numbers supplied here are exercise data, not a recommendation for any country. Check the adopted edition, relevant clause, National Annex, applicability conditions and all other limit states before any real design.
Let’s solve one together
Read the given values, follow each operation, then check what the result means.
Read the supplied values as one complete study case. Find qb and explain the result in the stated output unit.
- ρ · Air density
- 1.25 kg/m³
- vb · Basic wind velocity
- 30 m/s
Square the basic wind speed
Velocity pressure follows kinetic energy, which depends on speed squared.
(30)^2 = 900 m²/s²Convert to basic velocity pressure
Multiply by half the air density to obtain pressure in pascals.
0.5 × (1.25) × (900) = 562.5 Pa
Does this worked answer make sense?
Doubling wind speed multiplies qb by 4. Doubling density doubles qb; zero speed gives zero velocity pressure.
A second worked example — different values
A second case uses different data. Predict which way the answer will change, then calculate it without reusing the first answer.
- ρ · Air density
- 1.2 kg/m³
- vb · Basic wind velocity
- 40 m/s
Square the basic wind speed
Velocity pressure follows kinetic energy, which depends on speed squared.
(40)^2 = 1600 m²/s²Convert to basic velocity pressure
Multiply by half the air density to obtain pressure in pascals.
0.5 × (1.2) × (1600) = 960 Pa
Now try your own values
Change a value or its unit. The same method will show your calculation, step by step.
Results update only when you calculate. The lesson example above stays unchanged.
Your turn — check your understanding
Solve this separate case yourself. Use only the values below; the two worked examples use different data. Give the requested result in the selected unit.
- ρ · Air density
- 1.25 kg/m³
- vb · Basic wind velocity
- 24 m/s
Find: Learn: Basic wind velocity pressure
A hint, not the answer
The kinetic-energy expression contains one half of air density times speed squared. Squaring speed explains why a modest speed increase can produce a much larger pressure increase.
Use air density in kg/m³ and basic wind speed in m/s. The result is kg/(m·s²) = Pa. Convert km/h to m/s by dividing by 3.6 before squaring.
Show the full practice solution
Compare the steps with your work; revealing a solution does not mark the lesson complete.
Square the basic wind speed
Velocity pressure follows kinetic energy, which depends on speed squared.
(24)^2 = 576 m²/s²Convert to basic velocity pressure
Multiply by half the air density to obtain pressure in pascals.
0.5 × (1.25) × (576) = 360 Pa
Avoid the common trap
Do not input wind speed in km/h while selecting m/s. Do not omit the square or confuse basic velocity pressure qb with peak velocity pressure qp.
When this method applies — and when it does not
Terrain, height, turbulence, orography, directionality, peak pressure and surface coefficients are not calculated here. The result alone cannot be applied as a building’s final design wind pressure.
For study and understanding, not approval of a real structure, site operation or design. Apply the correct standard, National Annex and professional review to actual engineering work.
One idea understood. Keep going.
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Sources & further reading
References open in a new tab and explain the underlying principles. The teaching text and examples here are SimpleFlick’s own; the source organisations have not endorsed this calculator.
Reading focus: Basic wind velocity pressure. Action-specific reading: EN 1991-1-1 for self-weight, EN 1991-1-3 for snow, and EN 1991-1-4 for wind. National and site data are not generated by this lesson.
Lesson updated: · Both examples and the separate practice case are checked against an independent high-precision numerical implementation. This verifies arithmetic for the stated model, not engineering certification.