Drag Force Calculator

Wind drag from speed, area, and Cd with power shown.

What it does

Air pushes with the square of speed. Thirty meters per second on two square meters at Cd 0.3 gives about 331 newtons, near 74 pounds force. Doubling to sixty would quadruple toward 1300.

The tool above takes speed, frontal area, and Cd and returns drag force, dynamic pressure, and push power. The defaults 30 m/s with 2 m2 match the worked example, so the page opens showing 330.8 N. Switch to imperial for mph.

Dynamic pressure q = half rho v squared with rho 1.225 kg/m3. Force multiplies by Cd and area. Power multiplies by speed again. Here q is 551.3 Pa, force 330.8 N, power 9923 W.

Use this for signs, racks, and cars in steady air. Gusts, yaw, and ground effects shift real loads. Structures need codes beyond free field drag.

This page shows the formulas, one full hand checked example at 30 m/s, a reference table, and practice checks that run through the tool in both unit systems.

How to use

1. Pick Metric (m/s, m2) or Imperial (mph, ft2).
2. Type speed in the active unit.
3. Type frontal area facing wind.
4. Type Cd, car 0.3, plate 1.1.
5. Read Drag force as the main result.
6. Read Power to hold that speed.

Formula

v

Speed in m/s.

A

Frontal area.

Cd

Shape factor 0 to 2.

Sea level rho 1.225 here. Altitude thins air and cuts drag. Gusts need peak speeds, not averages.

Worked example

Reference table

Limits

• Steady sea level air assumed.
• Single Cd assumed. Real Cd shifts with yaw and Reynolds.
• No gusts here. Use peak speeds for peaks.
• Structures need code combos beyond free drag.

Common mistakes

• Forgetting square on speed.
• Mixing mph with m/s in one product.
• Using plan area instead of frontal.
• Reading pressure Pa as force N.
• Expecting linear rise with speed.

Try it yourself

Quick checks. Answers sit tucked under each question.

Questions

Sources

• NASA
• BIPM: SI Brochure

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