An Anemometer is an instrument to measure wind speed. There are many type of designs, some are extremely complex. This guide will help you build a simple and free anemometer that works. Follow it step by step, you can not go wrong.

What you will need: Cardboard (or light material such as fibre), 4 Cups (plastic or other type, but must be light), a rod or pencil and a base (wood, fibre or modelling clay).

Step One: Paint one of the cups so that it is different from the others.

Step Two: Cut two strips of cardboard (or fibre) in equal length. 30 cm long and 5 cm across, or other similar size ratio will work well.

Step Three: Paste or tape one cup on each end. You should now have two strips of cardboard with four cups secured to each side. The four cups should be aligned. Open ends should all face the same direction.

Step Four: Make a cross with both strips of cardboard attached to the middle. Secure them. You should now have a cross with a cup on each end side.

Step Five: In the exact centre of the cross attach a rod or pencil. The cross should be attached to the rod but it should also spin freely on it’s axis.

Step Six: Secure the rod or pencil to the base. Some people use plasticine (modelling clay) others use wooden or plastic supports. The important things is that it should be firm. Remember you are working with winds.

Step Seven: Make sure the cross and cups turn and the base is firm.

Step Eight: Give it a test. Put your Anemometer out in the wind. You should see the cup of a different colour go round and around. The instrument should move with ease and it should be firm.

Step Nine: Count the revolutions per minute. Using a watch count how many times you see the coloured cup take a spin. You will use this count number (called revolutions) to calculate the wind speed. You can make different counts to get average speeds.

Step Ten: How to Calculate wind speed. Measure the diameter of the Anemometer in metres. If it is 20 cm then it would be 0.20 metres. The diameter would be the distance from centre of the cup, to the centre of the opposite cup. Now, multiply the diameter by 3.14 (π). Your result will be the Circumference. Multiply Revolutions (RPMs) by Circumference (C), you will get the speed per minute(s/m). Now multiply the speed by 60 minutes to get speed per hour (s/h). The result is the wind speed.

You can change this design to make it more professional. Use more high end materials. Instead of ordinary cups use plastic or fibre cups. Instead of pencils use fibre roads. Instead of counting revolutions by eye. Attach an electronic digital revolution counter. The digital revolution counters are not very expensive. They will mark average speeds as well as maximum and minimum speed.