Wind speed is the measure of how fast air is circulating horizontally within the atmosphere, a movement caused by differences in air pressure. For a homeowner, knowing the wind’s pace is practical for many reasons, including weather preparedness and maintaining structural safety. Understanding local wind conditions is important for planning gardening projects, deciding when to safely use outdoor items like trampolines or awnings, and assessing potential damage risk during storms. This knowledge provides insight into the local microclimate, affecting everything from energy consumption to the dispersion of pollutants.
Using Standard Instruments
The most common ready-to-use instruments for measuring wind speed at home are cup anemometers and vane anemometers. The cup anemometer features three or four cups mounted on a vertical shaft. The force difference between the concave and convex sides of the cups drives the rotation, causing the cups to spin.
This rotational speed is directly proportional to the wind speed. A sensor counts the revolutions per second, applying a conversion factor to translate this count into a standard speed unit like miles per hour (mph) or meters per second (m/s). Vane or propeller anemometers, often used as handheld devices, work similarly, using a small propeller that spins when pointed directly into the wind.
The instrument’s tail, like a wind vane, keeps the propeller oriented toward the wind source for accurate reading. These instruments provide a simple digital readout, making them convenient for quick spot checks or permanent mounting on a home weather station. Cup anemometers are better for continuous outdoor monitoring because they do not need to be oriented into the wind.
Estimating Wind Speed Without Tools
When no instruments are available, wind speed can be estimated effectively using the Beaufort Wind Force Scale, an empirical measure developed in the early 19th century. This scale correlates observable environmental effects with specific wind force numbers and speed ranges. The lower levels of the scale, from 0 to 5, are most useful for everyday estimation around the home and garden.
- Force 0, “Calm” (less than 1 knot): Smoke rises vertically.
- Force 1, “Light Air” (1–3 knots): Smoke begins to drift, but wind vanes remain still.
- Force 2, “Light Breeze” (4–6 knots): Wind is felt on the face, and small wavelets appear on water surfaces.
- Force 3, “Gentle Breeze” (7–10 knots): Light flags extend, and leaves and small twigs are in constant motion.
- Force 4, “Moderate Breeze” (11–16 knots): Strong enough to raise dust and loose paper, and small tree branches begin to move.
- Force 5, “Fresh Breeze” (17–21 knots): Characterized by moderate waves with frequent whitecaps on water, and small trees start to sway.
Constructing a Simple DIY Anemometer
A functional wind speed indicator can be built using common household items. You will need four small paper or plastic cups, two plastic straws, a straight pin or thumbtack, tape or a stapler, and a pencil with an eraser. Create the rotor arms by crossing the two straws at their centers to form a perpendicular ‘X’ shape, securing them with tape or staples.
Next, attach one cup to the end of each of the four straw arms, ensuring all cup openings face the same direction to catch the wind. Mark one of the cups with a distinct color or dot to easily count the rotations. The center of the straw cross should then be attached to the top of the pencil eraser using the straight pin or thumbtack.
Do not push the pin too far into the eraser, as the arms must be able to spin freely with minimal friction. To calculate a rough speed, hold the pencil vertically and count the number of times the marked cup passes a fixed point over a set time (e.g., 30 or 60 seconds). This gives you the rotations per minute (RPM) by calculating the circumference of the rotor path.
Ensuring Accurate Measurement Readings
Obtaining reliable wind speed data requires following specific guidelines, regardless of the instrument used. Proper placement is paramount, as airflow can be significantly distorted by nearby objects. Obstructions like buildings, trees, and fences create turbulence, resulting in inaccurate readings.
For fixed installations, the sensor should be placed in an open area, ideally elevated above the roofline or any nearby structure. Meteorologists often use a standard height of 10 meters (about 33 feet) to minimize surface friction effects, but a consistent height of at least 5 feet from the ground is recommended for home use. If using a handheld anemometer, hold it at arm’s length away from the body to prevent interference from body heat or movement.
Wind speed is inherently variable, fluctuating constantly between sustained periods and brief, strong gusts. To capture a stable average, readings should be taken over a period of at least 30 seconds to a minute. This averaging helps distinguish the sustained wind speed (the average over a longer interval) from the quick, high-speed peaks known as gusts. Be mindful of the units, as wind speed is commonly reported in miles per hour (mph), kilometers per hour (km/h), or meters per second (m/s), and knowing the conversion factor is necessary for comparing data.