Parameter Types. Inconsistent Units converting Sqare Feet to GPM

[RD-k3migr]

I'm attempting to modify an automatic sizing roof drain I found on revitcity.
I would like to Convert the Roof area In Square Feet to Gallons Per Minute. With a variable of rainfall rate in inches per hour, which can vary from 1 to 6 depending on the location. (1 / 12 of a Cubic Foot * 7.48 Gallons in 1 cubic foot = .623 gallons per inch of rain fall per hour. Divide that by 60 to get .0104 gallons per inch of rain fall per minute.)

Below is what I thought the formulas would look like. However every time I try and formulate these parameters I get "Inconsistent Units" error, because the units are not the same I assume.
To Calculate GPM
I want a GPM parameter. "type" by "Flow" (for gpm units to carry thorough the connector.)

GPM = total area * rainfall rate * .0104
ex.. 3,340 sq/ft * 4 * .0104 = 139 GPM

Next I would like to Size the connector/pipe by gpm here is the formula I had in mind for that.
Pipe Size = if(and (gpm > 0, gpm <61), 0' 3", if(and (gpm > 60, gpm <121), 0' 4", if(and (gpm > 120, gpm <341), 0' 6", if (and (gpm > 340, gpm <711), 0' 8", if (and (gpm > 710, gpm < 1311), 0' 10")))))

Also Is there a way to pull the "Area" Parameter which my family would reside in, from the project into my family to use in this formula?

I hope this isn't too difficult to understand as it was difficult to explain. Any help or suggestions would be greatly appreciated. Also attached is the family that I'm trying to modify.

thanks,
ken.

[asommer]

Be careful, I don't think 1/12 of a cubic foot is a cubic inch.  more like 1/1728.  144 square inches in a square foot, x 12.

As far as the inconsistent units, you might have to use all bare numbers as a calculator would.  The Revit doesn't know how to do some of these conversions.

keep trying, it might suprise you what it can do.

[RD-k3migr]

Thanks,

I tried just using bare numbers. But my biggest problem is not being able to link the final number, to the connector in gpm.

[asommer]

Yeah, Looks like it won't work that way.  You can still set it up where you punch in the area and rainfall rate and get the end result, you would just have to manually enter the GPM value.