For study estimates only, not engineering design
Table of Contents
Table of Contents
Need the numbers before you pull wire or quote a job in the U.S.? These free online electrical calculators give you fast answers for voltage drop, wire size/AWG, single-phase & three-phase power, and kW↔kVA↔kVAR conversions. Because speed matters in the field, every tool is lightweight, clear, and tuned for typical NEC workflows.
Jump to: Calculate • Learn • Career
Start here: free electrical calculators
- Voltage Drop Calculator — single/three-phase, percent drop and suggested wire size.
- 1-Phase / 3-Phase Power Calculator — P-V-I-PF math with kW/kVA/kVAR.
- Battery Runtime Calculator (AC/DC) — capacity, depth-of-discharge, and efficiency.
- Transformer kVA Calculator — size a transformer from load kW/kVA.
- Energy Cost Estimator — estimate running cost from load, hours, and rate.
- Backup Generator Size Calculator — size a standby or portable generator from the loads you need to keep running.
- Electrician Career Transition ROI Calculator — training cost, lost income and payback time for a career change.
- Texas license timeline: when your hours reach each Texas license step.
Tip: If you work residential 120/240 V or commercial 277/480 V, these tools default to those values so you can move faster.
Studying for the Texas Journeyman exam? Calculations are one of its two timed parts. See what the Calculations part tests and how to solve each type, or try 70 free questions. All Texas electrician exams.
8 electrical calculators and Amp Sprint
The 8 electrical calculators and the Amp Sprint game, grouped by what you need them for. Each tool has its own page.
Basics and self-test
New to electrical work? Get fluent with volts, amps, ohms and watts first, then time yourself with the game.
- Ohm’s Law & Power Calculator — enter any two of volts, amps, ohms and watts to get the other two
- Series & Parallel Circuit Calculator — total value of resistors in series or parallel
- Amp Sprint — a timed game: see the watts and volts, call the amps, and see how fast you are
Local voltage, frequency and wire units
Voltages, frequency and wire units differ by country, so set your local conditions before you calculate.
- Voltage Drop Calculator — percent drop and a suggested wire size for your run
- Single / Three-Phase Power Calculator — kW, kVA and amps at your local voltage and power factor
- Inductive Reactance Calculator — XL and current at your local 50 or 60 Hz
Advanced
AC circuits, signal power and heating: questions that show up on licensing exams and on the job.
- Impedance Calculator — capacitive reactance, series RLC impedance and phase angle
- dBm to Watts Converter — convert between dBm, mW, W and dBW
- Joule Heating Calculator — H = I²Rt in joules, calories and BTU
The full toolkit: Calculate, Learn, Career
Every link below is a real, live page on this site — not a placeholder. Each card states exactly what you put in, what you get out, what it does and doesn’t cover, and its safety or regulatory boundary, so you know what you’re clicking before you click it.
Calculate
Ohm’s Law & Power Calculator
Input: any 2 of Voltage, Current, Resistance, Power
Output: the remaining 2 values, computed instantly
Scope: universal physics — no jurisdiction dependency
Safety / regulatory boundary: for learning/planning only; always verify final wiring and equipment ratings against your local code.
Series & Parallel Circuit Calculator
Input: a list of resistor values, and series or parallel mode
Output: total circuit resistance
Scope: universal physics — no jurisdiction dependency
Safety / regulatory boundary: for learning/planning only; not a substitute for measuring real installed resistance.
Single / Three-Phase Power Calculator
Input: voltage, current, power factor, and 1-phase or 3-phase
Output: kW, kVA, kVAR
Scope: universal formulas; US voltage defaults (120/240V, 208/277/480V)
Safety / regulatory boundary: pre-design check only; confirm against your utility service and local code before sizing equipment.
Circuit Breaker Size Calculator
Input: load amps or watts, voltage, and a breaker series (e.g. US 15/20/30A)
Output: the next standard breaker size
Scope: US-style breaker series by default; other regions use different standard series
Safety / regulatory boundary: does not replace conductor ampacity tables, code compliance checks, or an AHJ/engineer’s sign-off.
Voltage Drop Calculator
Input: current, one-way length, voltage, wire size/material
Output: percent voltage drop and a suggested wire size
Scope: US NEC-oriented 3% branch / 5% total guidance
Safety / regulatory boundary: a pre-design check, not a final design; always verify against your local code and installation conditions.
Learn
Electrician Fundamentals: Learn, Practice & Mock Exam
Input: nothing required to start — a short lesson, then a 10-question quiz
Output: a pass/fail score with explanations for each answer
Scope: universal fundamentals (Ohm’s law, basic circuit math) — not jurisdiction-specific
Safety / regulatory boundary: this is a free self-practice quiz, not an official certification or licensing exam, and it doesn’t replace your local code or a qualified electrician’s judgment.
Career
Global Electrician Career Paths
Input: your content language and target work location
Output: the matching regional pathway guide
Scope: currently Taiwan and Canada → British Columbia only — other regions not yet covered, stated honestly
Safety / regulatory boundary: educational information, not legal, immigration, or employment advice.
British Columbia Electrician Pathway Eligibility Self-Check
Input: your current experience, education, and work-authorization status
Output: an honest self-assessment of which BC apprenticeship entry path may fit you
Scope: British Columbia, Canada specifically — not valid for other provinces or countries
Safety / regulatory boundary: not an official determination; verify your actual eligibility with SkilledTradesBC before acting on it.
Why electricians use calculators instead of “head math”
On a long day it’s easy to miss a factor of 2L on single-phase, forget the √3 on three-phase, or mix up kW and kVA. Therefore, a reliable calculator prevents change orders, nuisance trips, and callbacks. In addition, it helps apprentices learn the pattern while keeping journeymen quick and consistent.
In short: use the Voltage Drop Calculator for long runs, the Power Calculator for load sizing, the Wire Size Calculator for conductor selection, the kW/kVA/kVAR Converter for power triangle math, and the PF Calculator for power-factor questions.
When should you use which electrical calculators?
- Sizing a branch circuit or feeder — start with Voltage Drop; if you’re near 3% at the branch or 5% total, bump the conductor.
- Figuring motor or EV charging load — use the 1ϕ/3ϕ Power Calculator with actual PF; as a result, your breaker and conductor choice matches real demand.
- Comparing copper vs aluminum — run the same current/length in the Wire Size Calculator; however, always check terminals and torque listings.
- Estimating generator/UPS size — convert with kW↔kVA↔kVAR and set a sensible PF.
Voltage drop: when is it critical?
- Long exterior runs: driveway lighting, detached garages, docks.
- Starting loads: well pumps, compressors, heat pumps, and EVSE—keep branch drop tighter than 3%.
- Low-voltage lighting & controls: even small absolute loss is a big percent at 12/24 V.
- Commercial three-phase: the geometry helps, nevertheless, check both feeder and branch because margins stack.
How this toolbox fits your learning path (skill tree)
Beginner → learn the P-V-I-PF triangle and try the 1ϕ/3ϕ power tool.
Intermediate → practice voltage drop and wire size decisions with a 3% / 5% target.
Advanced → layer on ampacity, derating, and OCPD coordination; then verify against your local code.
Extended reading about electrical calculators (internal links)
- Panel upgrades & breaker selection
- AFCI/GFCI protection basics →
/afci-gfci-guide - Copper vs Aluminum — wire size & ampacity →
/wire-size-ampacity
References (outbound links)
- NEC informational notes on voltage drop (3% / 5%)
- Engineering Toolbox — conductor resistivity tables
- NEMA/ANSI wire and AWG references
Disclaimer: These calculators are for education and pre-design checks. Therefore, final selections must follow the NEC and local amendments, equipment listings, and the AHJ or project engineer. When in doubt, upsize and document your assumption.
U.S. system presets in these calculators
The calculators ship with the three services you meet most often in U.S. buildings, all at 60 Hz, so you do not have to type the voltages every time.
- 120/240 V split-phase: standard residential service. 240 V between the two hot legs, 120 V from either leg to neutral.
- 120/208Y V three-phase: light commercial. 208 V line to line, 120 V line to neutral, which is why ordinary receptacles still work on it.
- 277/480Y V three-phase: commercial and industrial. 480 V for motors and large equipment, 277 V line to neutral for lighting.
The wye presets give you both a line-to-line and a line-to-neutral value, so a single-phase load taken from a three-phase panel is calculated correctly. If your service is a 240 V delta, enter the voltages manually; the presets assume a neutral.
These three cover most U.S. work. For 230/400 V systems and mm² conductors, switch the units in the calculator instead of using a preset.
FAQ
Yes—formulas follow common industry practice; however, you still need to check ampacity, installation method, ambient temperature, grouping/derating, and breaker coordination.
Not for branch circuits, but feeders and services in light commercial often use three-phase. Consequently, it helps to understand both.
Aim for ≤3% on a branch and ≤5% total feeder + branch. In addition, sensitive loads may need tighter limits.
Absolutely. Meanwhile, you can toggle m ↔ ft and Cu ↔ Al; the calculators update instantly.
