Guides & Explanations
Plain explanations of the math behind our calculators — how each formula works, what the result means, and the mistakes people make reading it.
All Guides
How to Calculate Cubic Yards (Without Getting It Wrong)
The ÷27 rule, why depth in inches trips everyone up, and how much extra to order.
Read guide →Reverse Sales Tax: How to Find the Price Before Tax
Why you divide instead of subtract, and the mistake that makes the tax look bigger than it is.
Read guide →How to Calculate Your GPA (College and High School)
The credit-weighted method, the 4.0 grade-point scale, and why credit hours change everything.
Read guide →How to Calculate Standard Deviation (Step by Step)
The difference between sample and population, why you square the deviations, and the n−1 rule.
Read guide →How to Calculate Molar Mass From a Chemical Formula
Add up atomic weights, handle parentheses, and turn grams into moles for any compound.
Read guide →How Much Should You Tip? A Simple US Tipping Guide
Standard tipping percentages, the quick 20% mental math, and how to split a bill with tip.
Read guide →The Ideal Gas Law (PV = nRT) Explained
What each variable means, why temperature must be in kelvin, and the molar volume at STP.
Read guide →How to Calculate Gas Cost for a Road Trip
The two-step formula, using real-world MPG, and why fuel economy matters more than price.
Read guide →Looking for a different calculator?
CalculatorPlus has free tools across finance, construction, math, health and more — each one showing the formula and a worked example.