Q&A for How to Measure Rain

A gauge should be unprotected from the elements in all directions, it should be kept clean inside, and it should be emptied every day at the same time.

Use mm, cm, or inches.

The same way. Just measure and report in centimeters instead of inches. If you measured in inches and want to convert to centimeters, see How to Convert Inches to Centimeters .

There could some some deviation on the ground level due to wind direction, buildings, tree, etc. Putting the rain gauge 30 meters above the ground can negate some of these factors.

Daily rainfall is measured over 24-hour periods beginning at local midnight (so, 12 am to 12 am).

The surface area increases as the rain gets higher in the gauge, therefore the gradation is smaller as the gauge fills.

Inches, centimeters, feet, etc. It just depends on what you're going to use the data for.

1/10" = 0.100". 1/8" = 0.125". So for casual measurement, there is not a lot of difference. But if you want to be more specific, there is 1¼ tenths in an eighth of an inch.

It depends entirely on the lateral dimensions of the rain gauge. 500 ml of water poured into a wide gauge would show a depth less than the same 500 ml poured into a narrow gauge.

No. Rainfall is measured in linear dimensions (inches or millimeters, for instance) rather than by volume (cubic inches or liters).

You can assume 175 mm of rain throughout your parcel of land. Typically there's not much variation in rain depth among adjacent locations, although it's impossible to know for sure without measuring at each location.

If the gauge overflows, you won't have an accurate measurement. As for the diameter, oddly enough it doesn't matter: while the volume of water in the gauge does vary with the diameter, the depth of the water does not (and the depth is all you care about).

You don't. Square gauges work just fine. No matter the shape, the sides of the gauge have to be straight and vertical (unless you're using a professionally graduated gauge).

As with any set of data, to find the average you add up all the annual rainfall totals into one large depth, and then divide that depth by the number of years of data you're considering.

If each bottle is a perfect cylinder (even if they have different diameters), each will contain the same depth of rainwater (assuming they are next to each other in the rain).

The time frame is however long it's been since you last emptied your gauge.

Nobody's lying. Either someone's equipment is faulty, or your specific location gets more rain than theirs.

Most crops -- plants of any sort, actually -- need 1 or 1½ inches of water every week during the growing season.

It doesn't matter. Two cylinders of different diameters, when placed side-by-side, will collect the same depth of rainwater in any given period of time (assuming equal exposure to the weather).

Actually, no. A container with a larger diameter will collect a greater volume of rainwater, but the depth will be the same, regardless of the diameter. Thus the rainfall measurement will be unaffected by diameter (since we're measuring depth, not volume).

That 11.33 (inches) is a monthly average of the amount of rain collected in a certain gauge over a three-month period. It does not suggest that the rain penetrated the soil to any particular depth. (That's a completely different discussion that involves composition and moisture content of the soil.)

No. While the volume of rain collected increases with a gauge's diameter, its depth does not. The depth measurement remains the same regardless of the gauge's diameter.