Math for Electricians

Electrical math is the backbone of safe, code-compliant work. Whether you’re sizing wire for a feeder run, calculating voltage drop on a long circuit, or figuring out conduit fill, the math is what separates a professional installation from a callback. These aren’t abstract formulas — they’re the calculations you’ll use on every job.

What You’ll Learn

This section covers the math skills tested on journeyman and master electrician exams and used daily on the job:

• Ohm’s Law — the foundation of all electrical math. Voltage, current, and resistance relationships that every electrician must know cold.
• Electrical Power Calculations — watts, volt-amps, and the power formula. Sizing circuits, calculating loads, and understanding demand factors.
• Series and Parallel Circuits — how resistance, current, and voltage behave in different circuit configurations.
• Voltage Drop Calculations — using the VD formula to ensure circuits meet NEC requirements for conductor length.
• Wire Sizing — selecting the correct conductor size based on ampacity, temperature ratings, and derating factors.
• Conduit Fill Calculations — determining how many conductors fit in a given conduit size per NEC Chapter 9.
• Conduit Bending Math — calculating offsets, saddle bends, and stub-ups using trigonometry and multipliers.
• Box Fill Calculations — counting conductor equivalents and selecting the right junction box size per NEC 314.16.
• Transformer Calculations — turns ratio, primary/secondary voltage and current relationships.
• Electrical Cost Estimation — calculating kilowatt-hours, energy costs, and basic job pricing.

Why This Matters

Every electrician exam tests these calculations:

• Journeyman exam — Ohm’s law, voltage drop, conduit fill, and box fill are the most-tested topics
• Master exam — adds transformer calculations, demand factors, and load calculations
• NEC compliance — voltage drop, wire sizing, and conduit fill calculations determine whether your work passes inspection
• Job pricing — accurate material and labor estimates keep your business profitable

Each topic uses real-world examples with NEC-standard values, actual wire gauge sizes, and practical job scenarios.

Where to Start

If you’re new to electrical math, start with Ohm’s Law — it’s the formula everything else builds on. Once you’re comfortable with V = IR, move to Power Calculations, then Voltage Drop and Wire Sizing.

If you’re studying for your journeyman exam, prioritize:

1. Ohm’s Law
2. Voltage Drop
3. Conduit Fill
4. Box Fill

Every page includes:

• Clear formulas with practical explanations
• Worked examples using real wire sizes and NEC values
• Practice problems with detailed solutions
• Common exam question patterns