when converting the Rainfall Rate unit from mm per HR (Sq. m) to inch per HR (Sq. ft) why are they multiplying by 25.4 only and not considering the conversion from m2 to ft2
for example
mm/m2 --> in/ft2 = (1/25.4 in)/(10.764 ft2) = 0.0036 in/ft2
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1$\begingroup$ Who are "they"? You should provide more context to the question. Welcome to Earth Science SE! $\endgroup$– Jean-Marie PrivalCommented Sep 4 at 15:37
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Rainfall rate as mm/hr or in/hr is in terms of length, not volume. You're thinking of it as a "per unit area" rate, but that would be reported in volume or mass, not length. Another way to put it is that the volume-per-area is already implicitly solved by reporting in units of length.
Imagine using a physical rain gauge with depth markers. If you convert from mm to inches, does the area occupied by the gauge change?
Note that your mm/m2 calculation would have rainfall being measured in units of inverse length and inverse time, which doesn't make physical sense.
