Do You Have a Rain Gauge?

YES you do; but you may not know it!

This project is rated: MODERATE

Materials needed:
  • Glass container
  • Masking tape
  • Marking pen
  • Liquid measuring cup
  • Calculator

First, I will give the necessary technical details; and then I will give you specific details for a particular common container.

Your container can be a jar, a rectangular or round pan, a funnel on top of a glass, or any open top container. Just select a container and sit it outdoors in an open area away from trees or buildings. Then wait for rain.

After the rain has stopped, empty your “rain gauge” into a measuring cup or pitcher that is graduated in ounces. Determine how many ounces you have collected (you may want to estimate decimal fractions of an ounce also.)

Now comes the tricky part. You need to make some calculations. Some of these you can do once before you put out your “rain gauge.” Measure the very top opening of your “rain gauge.”

If it is rectangular, measure the width (W) and the length (L). Then calculate the total area of the opening with the formula:

AREA = W times L

If the opening is a circle, measure the diameter (D) (that’s the longest measurement across the circle.) Then calculate the total area of the opening with the formula:

AREA = .79 times D times D

Once you know the area, you can use the following formula to determine the amount of rainfall in inches:

INCHES = 1.8 times OUNCES divided by AREA

There, isn’t that easy?

If you don’t think so, I will give you a specific example, at right, below the project image.

Jar

Project Instructions

The project image above approximates a typical glass jar, in this case a “Miracle Whip” jar.

This jar has an opening whose inside diameter is approximately 2.42 inches. This yields an area of 4.63 square inches. The rainfall formula becomes:

INCHES = 1.8 times OUNCES divided by 4.63

This can be simplified by dividing 1.8 by 4.63. The simplified formula is:

INCHES = .39 times OUNCES

Advanced Instructions

Perhaps you would like to calibrate your “rain gauge.”

Take a piece of masking tape and attach it vertically to the outside of your jar. Measure out 2.56 liquid ounces of water. (You may find this difficult and you may need a laboratory graduate to measure this amount accurately. If your graduate is calibrated in milliliters, measure 75.7 milliliters.)

Now pour the measured water into your “rain gauge.”

Using permanent ink draw a horizontal line on the masking tape at the level of the water. Mark it “one inch.”

Add another 2.56 ounces of water and mark the level, “two inches.”

Continue adding the same amount of water and marking succeeding levels as 3, 4, 5, etc. inches.

Now your gauge is complete.

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