Write These Formulas in Your Code Book—You’ll Be Glad You Did
One of the best things you can do is write your most important formulas directly into your NEC book. Most testing centers allow brief, handwritten notes—so don’t miss the chance to give yourself a huge advantage. Just double-check your exam bulletin to make sure notes are permitted.
When you're under time pressure during the exam, flipping through your book to search for formulas can waste valuable minutes. Having them already written where you can find them quickly may save you from second-guessing and keep your momentum going.
🔗 Before you go any further, download your free Electrical Formulas Cheat Sheet.
It includes must-know formulas for motor calculations, box fill, conduit fill, transformers, EIR, PIE, and more.
Why You Need These Formulas
The electrical license exam isn’t just about finding the right Code section—it’s about knowing how to apply it. You'll likely face questions that require calculating current, resistance, voltage drop, and power. These formulas are the tools you'll rely on.
While memorization is key, it’s also smart to have the formulas written in your book for quick reference—if allowed. That way, you're not stuck trying to remember a formula mid-exam. If your testing site doesn’t allow notes, be sure these formulas are committed to memory well before exam day.
Here’s a list of the most common PIER (Power, Current, Voltage, Resistance) formulas used in electrical exam preparation. These are foundational for solving many types of calculation questions on the electrician licensing exam.
PIER Core Formulas
These formulas are based on the relationships between P (Power), I (Current), E (Voltage), and R (Resistance).
Power Formulas
- P = I × E
Power = Current × Voltage - P = I² × R
Power = Current squared × Resistance - P = E² ÷ R
Power = Voltage squared ÷ Resistance
Current Formulas
- I = P ÷ E
Current = Power ÷ Voltage - I = E ÷ R
Current = Voltage ÷ Resistance - I = √(P ÷ R)
Current = Square root of Power ÷ Resistance
Voltage Formulas
- E = P ÷ I
Voltage = Power ÷ Current - E = I × R
Voltage = Current × Resistance - E = √(P × R)
Voltage = Square root of Power × Resistance
Resistance Formulas
- R = E ÷ I
Resistance = Voltage ÷ Current - R = E² ÷ P
Resistance = Voltage squared ÷ Power - R = P ÷ I²
Resistance = Power ÷ Current squared
Don't Forget the Basics: PEMDAS
One often overlooked but critical reminder: review the order of operations. A surprising number of exam-takers make mistakes on simple math because they forget how to properly work through multi-step calculations.
PEMDAS = Parentheses, Exponents, Multiplication & Division, Addition & Subtraction
A fun way to remember it: “Please Excuse My Dear Aunt Sally”
Whatever phrase helps you recall it use it. Just don’t lose points on something that simple.
Final Thoughts
✅ Download the Electrical Formulas Cheat Sheet now so you can start reviewing and writing them into your Code book while you study.
If notes are allowed during your exam, this will give you a major edge. If not, you’ll still be glad you took the time to master them early. These formulas are more than just shortcuts—they’re critical thinking tools you’ll use on exam day and throughout your career.
Start now. Get organized. Know your formulas.
You’ve got this.
