So then, your **equation** is this...

G = 3 * L * (I ^ 1.5) * 1440 / 1000000

where G is Million Gallons Per Day, L is Length and I is Inches (going over
the weir). Multiplying both sides by 1000000 and dividing both sides by L, 3
and by 1440 gives this rearrangement...

I ^ 1.5 = (1000000 * G) / (3 * 1440 * L)

Now, the 1.5 power is the same as the 3/2 power, so if we raise both sides
to the 2/3 power, we will have isolated I..

I = ((1000000 * G) / (3 * 1440 * L)) ^ 2/3

Assuming the Million Gallons Per Day value was stored in G1, and the Length
value was stored in L1, then your worksheet formula should be...

= ((1000000*G1)/(3*1440*L1))^(2/3)

Rick


"Shawn" wrote in message
...
Here is the formula set up to solve for MGD (Million Gallons per Day).
=3*936*A21^1.5*1440/1000000
936 is the length in inches.
A21 is a cell with the inches going over the weir.
1440/1000000 is to convert the gallons per minute to MGD.
What I want to do is set up another formula where the desired MGD could be
entered in a cell and the result would be the inches to let flow over the
weir.
(The practical application of all this is to set movable gates on a dam.)

"Rick Rothstein (MVP - VB)" wrote:

Show us the equation you have for calculating flow over a horizontal
weir...
there is no way we can help you isolate the "X" in "X^1.5" unless we know
the rest of the equation.

Rick


"Shawn" wrote in message
...
I have a formula for finding the flow over a horizontal weir. ( gpm = 3
*
weir L ins. * overflow ins. 1.5th) I want to set up an Excel formula to
give
the result as the overflow inches. ("X" in "X^1.5") How do I do that?