Ohm's Law Calculator & Electrical Math Practice Lab
Solve for voltage, current, resistance, or power, then practice the same electrical math yourself. The lab also includes series and parallel resistance calculators, targeted feedback, and printable practice sets.
Calculator
Solve V, I, R, and P
Enter exactly two known values. The calculator derives the other two and shows the equations used.
Enter two positive values, then select Calculate.
Show calculation steps
Formula wheel
Pick the value you want to find
Series and parallel resistance
Equivalent resistance calculator
Add up to eight resistors and choose series or parallel.
Start with the two resistor values above.
Practice
Electrical math practice lab
Work randomized problems and get a worked solution when you miss one.
Ready when you are.
Select Start practice to generate a problem.
Curious about the trade?
Enjoying this kind of problem solving?
Electrical training builds on this foundation with code, drawings, safety, tools, wiring methods, troubleshooting, and supervised hands-on work. If this math clicks for you, explore what electrician training actually involves before choosing a program.
Explore electrician schools and training or see the steps to become an electrician.
Printable practice
Generate an electrical math worksheet
Create a fresh 10- or 20-question set with an answer key and worked solutions.
Generate a set when you are ready.
About this Ohm's Law calculator
This free electrical math lab combines a four-variable Ohm's Law calculator, an interactive formula wheel, a series and parallel resistance calculator, randomized practice problems, and printable worksheets. It is meant to help learners understand the math rather than only grab an answer.
Ohm's Law and electrical power formulas
Ohm's Law relates voltage, current, and resistance. The basic relationship is V = I x R. Electrical power adds the relationship P = V x I. Combining those two equations produces the other useful forms below.
| Find | Useful formulas | Standard unit |
|---|---|---|
| Voltage (V) | V = I x R; V = P / I; V = sqrt(P x R) | volt (V) |
| Current (I) | I = V / R; I = P / V; I = sqrt(P / R) | ampere (A) |
| Resistance (R) | R = V / I; R = V^2 / P; R = P / I^2 | ohm |
| Power (P) | P = V x I; P = I^2 x R; P = V^2 / R | watt (W) |
Series vs. parallel resistance
Resistors in series add directly: Rtotal = R1 + R2 + R3 + .... Parallel resistance uses reciprocal addition: 1 / Rtotal = 1 / R1 + 1 / R2 + 1 / R3 + ....
A quick error check helps with parallel problems: equivalent parallel resistance must be lower than the smallest branch resistance. If your result is larger than every branch, you probably used the series rule or forgot the final reciprocal step.
How the practice lab helps
The practice engine creates new numbers each time instead of recycling one fixed test. When a wrong answer closely matches a predictable math error, the lab can point out the likely issue. Otherwise, it simply shows the correct formula and worked solution. It does not invent a personality score, apprenticeship-readiness score, or other fake precision from a handful of questions.
Why these skills appear in electrical training
Basic DC circuit theory is part of mainstream electrician training. The Electrical Training Alliance describes direct-current instruction that progresses through basic circuits, series circuits, parallel circuits, and combination circuits. NCCER's current Electrical curriculum also places electrical theory and circuit fundamentals in Level 1.
That is different from an apprenticeship entrance or aptitude test. General algebra, arithmetic, and reading may be tested before training begins, while circuit theory is taught as technical instruction. For admissions-style preparation, use our mechanical aptitude practice tool where relevant rather than treating this page as an entrance exam.
What this calculator does not determine
This page intentionally does not size conductors, breakers, services, feeders, motors, transformers, boxes, raceways, or protective devices. It does not determine code compliance. It also does not model AC impedance, reactance, phase angle, power factor, harmonics, or equipment-specific inrush behavior.
For other electrical tasks, use the electrical field planner, conduit bending calculator, or conduit and box fill calculator. Physical electrical work must follow applicable code, manufacturer instructions, and qualified supervision.
Electrical math FAQ
What is Ohm's Law?
Ohm's Law describes the relationship among voltage, current, and resistance in an ohmic circuit: V = I x R. Rearranging the same equation lets you solve for current or resistance.
What is the difference between Ohm's Law and Watt's Law?
Ohm's Law connects voltage, current, and resistance. The electrical power relationship P = V x I connects power, voltage, and current. Combining them produces formulas such as P = I^2 x R and P = V^2 / R.
Why is parallel resistance lower than the smallest resistor?
Adding a parallel branch creates another path for current and increases total conductance. Since resistance is the reciprocal of conductance, equivalent resistance drops below the resistance of any single branch.
Can I use this calculator for AC circuits?
Not as a complete AC design tool. This calculator treats values as ideal resistive DC magnitudes. Real AC circuits can involve impedance, phase angle, reactance, power factor, harmonics, and equipment-specific behavior.
Is this an electrician aptitude test?
No. This lab teaches circuit math. Apprenticeship aptitude tests may emphasize general algebra, arithmetic, and reading rather than electrical theory.
Can I use the answers to size wiring or breakers?
No. Real installations require code-compliant design and equipment-specific information that this learning tool does not model.
Sources
- OpenStax Physics: Key Equations - Ohm's Law, series resistance, parallel resistance, and electric power.
- Electrical Training Alliance: Electrical Theory / Direct Current - basic DC, series, parallel, and combination circuit training.
- NCCER Electrical Curriculum, 12th Edition - current 2026 electrical training structure and Level 1 electrical theory.
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