Wind Force

Wind Load Calculator

Use this calculator to compute the force of the wind on a given surface area:


It is natural to assume that if the wind speed increases from 5 to 10 mph then its force will double. But that isn't correct. The effective force of the wind actually increases 400%! If the wind further increases to 15 mph, then the effective force is 900% greater than it was at 5 mph.

The generic formula prescribed by the American Society of Civil Engineers for calculating wind load is Wind Pressure Per Square Foot x Surface Area in Square Feet, where:

Wind Pressure Per Square Foot = .00256 x Wind Velocity in MPH2

Sailors quickly learn this once they realize that sailing in 15 mph of wind is completely different than sailing in 5 mph. The difference is so dramatic that most sailors won't even venture out in winds much over 15 mph.

The purpose of this page is to provide a resource to help compare different wind velocities and predict how those changes may affect a given boat.

Beaufort Scale

The Beaufort Scale is a measurement of wind velocity based on observed conditions at sea and on land. It was developed in 1805 by Francis Beaufort, a Royal Navy officer, and remains a very practical and handy means of expressing wind velocity without the need for instuments. The table below shows the 13 levels of the Beaufort Scale:

0Calm< 1 knot
1Light Air1-3 knots
2Light Breeze4-6 knots
3Gentle Breeze7-10 knots
4Moderate Breeze11-16 knots
5Fresh Breeze17-21 knots
6Strong Breeze22-27 knots
7Near Gale28-33 knots
8Gale34-40 knots
9Strong Gale41-47 knots
10Storm48-55 knots
11Violent Storm56-63 knots
12Hurricane Force>= 64 knots