compute box for siemens step 7?

In Allen-Bradley PLC software a compute
box exists where you can write mathematical
formulas even with floating point numbers.
Example=(((3.1415927* 15)|17.25)+125.345)
In Siemens step 7 does an instruction
such as this exist anywhere or must
you use a single box for each mathematical
equation?

Sorry, no

compute is indeed a very handy instruction in the AB PLC. There is no such thing in S7.
I can only recommend to master S7 math using STL.
If you are familliar with the good old HP calculators that sported "reverse polish notation", then you wont find the use of "accumulators" in S7 to be too difficult.

Another way is if you are familiar with high level programming is to code your blocks in scl. This is a high level programming language much like pascal.

SCL is the answer. The quickest is STL. I am assuming the "pipe" command is division.

L 3.141593e+000
L 1.500000e+001
*R
L 1.725000e+001
/R
L 1.253450e+002
T "Example"