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Rainfall converter: mm, inches, L/m²

Convert a rain amount between millimeters, centimeters, inches and liters per square meter. 1 inch of rain is exactly 25.4 mm, and 1 mm of rain is 1 liter on each square meter.

Result

254mm

1 in = 25.4 mm

In the rain gauge: 10 in = 254 mm

Quick challenge

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Guess the conversion before you calculate it. How many can you get in a row?

How it works

Rainfall is measured as the depth of water that would cover flat ground if none ran off or soaked in. Weather services outside the United States give it in millimeters; the US National Weather Service gives it in inches. Because a liter is a cubic decimeter, 1 liter spread over 1 square meter makes a layer exactly 1 mm deep: millimeters and liters per square meter are the same number.

All units compared

All units compared
UnitSymbolValue in millimeters
millimetermm1 mm
centimetercm10 mm
liter per square meterL/m²1 mm
inchin25.4 mm

Frequently asked questions

How many mm in an inch of rain?

Exactly 25.4 mm, because the inch is defined as 2.54 cm.

Is 1 mm of rain really 1 liter per square meter?

Yes: 1 L = 1 dm³, and 1 dm³ spread over 1 m² (100 dm²) is 0.01 dm deep, which is 1 mm.

How much is 1 inch of rain on a roof?

About 0.62 US gallon per square foot (144/231). The rainwater harvesting calculator does the math for a whole roof.

How many millimeters are in 1 inch?

1 inch = 25.4 millimeters. The other way round, 1 millimeter = 0.0393701 inches.

How many inches are in 1 millimeter?

1 millimeter = 0.0393701 inches. The other way round, 1 inch = 25.4 millimeters.

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