I often hear people saying, it's no big deal, or I am no […], etc. I was wondering if it is acceptable to say it is no calculus in a college essay.
I think you're probably looking for an idiom like
It's not rocket science.
It's not brain surgery.
or, as some wags have it,
It's not rocket surgery.
This is one of those cases where modifying a cliché to make it fresher doesn't quite work. Saying "It's not calculus," while reasonable in a certain context, would not have currency among the general population and would not be readily understood to mean something easy or inconsequential.
EDIT: I answered with "not" constructions because I figured the OP would accept any negative construction, and as Scott Mitchell points out in his comment "not" certainly works better than "no" in the OP's example.
I would not risk using "It is no calculus". You might be meaning "It is not as hard as (differential or integral) calculus", in which case, say so. Or you might be referring to a logical system and stating "That isn't a calculus; it is merely an algebra", in which case, say that instead. Your original is ambiguous, therefore (at least, without the larger context to guide us), and probably too informal for a college essay.
It would depend on context. This is certainly no idiom.
… that I am familiar with.
I think you can certainly say "it's no calculus" if the context is correct. (What can't you say if the context is correct?)
For instance, the following sentence seems entirely plausible to me:
Horseback riding may have been challenging, but it was no calculus.
The implication here is that calculus was very difficult for you. It's important to note, though, that the emphasis of the sentence switches from horseback riding to calculus itself; the reader would probably expect the paragraph to transition into a discussion of the difficulties of calculus.
Contextually, it would make most sense as the introductory sentence to a paragraph about learning calculus, coming on the heels of a paragraph about the challenges of horseback riding.
So to answer your question, you can absolutely say it. Just be sure it's what you want to be saying.
I would say that the phrase "it is no calculus" could be used in an essay, but only under very specific circumstances, and for courses (Mathematics or Computer Science) that do not normally call for the types of essays that such a phrase would be used in anyway.
Most non-mathematicians use the term calculus to refer to a specific type of calculus -- that of differential and integral calculus developed by Isaac Newton.
Mathematicians (and Computer Scientists) use the term calculus to refer to a set of formula that can be used to define the changes in systems that incorporate some element of change. Examples of systems of calculus that have been defined include:
Relational Calculus: formulation that define ways to define a relational system and queries on that system. This is the basis of SQL databases.
Lambda Calculus: provides a formal definition system for data, functions and recursion. This calculus is the basis for the computer language LISP.
Predicate Calculus: is a formal definition of first order logic and the inferences and deductions that it is capable of. The computer language Prolog is based on this form of calculus.
So, if you have a system of equations of formulas, but it does not have the properties that it needs in order to be considered a type of a calculus, you could say that the system "is no calculus". But that is stretching things a bit.