Free Electrical
Calculators for
US Engineers
Professional-grade tools for 3-phase power, cable sizing, VFD selection, and phase comparison — built on NEC standards, optimized for electricians, engineers, and energy professionals across the United States.
All-in-One Electrical Engineering Calculator Suite
Whether you’re sizing conductors for a commercial build, selecting a VFD for a pump motor, or comparing single-phase versus three-phase systems for a facility upgrade — Solvebility’s electrical calculators deliver fast, NEC-compliant answers without spreadsheets or subscriptions.
Our tools are used by licensed electricians, electrical engineers, facility managers, and energy consultants across the US — from quick field checks on a smartphone to detailed design reviews at the office. Every formula is validated against industry standards including NEC 2023, IEEE standards, and NEMA motor ratings.
Electrical Calculator Tools
Four specialized calculators covering the most common electrical engineering calculations — available free, right in your browser.
3-Phase Power Calculator
Calculate real power (kW), apparent power (kVA), line current (amps), and system efficiency for any three-phase load — used for panel sizing, breaker selection, and utility billing verification.
- Real power (kW) & apparent power (kVA)
- Line current per phase (amps)
- Power factor correction guidance
- Supports 208V, 480V, 600V systems
- Balanced & unbalanced load modes
VFD Sizing Calculator
Determine the correct Variable Frequency Drive horsepower and ampacity for AC motor applications — accounts for service factor, duty cycle, and application margins per NEMA standards.
- Motor HP to VFD HP selection
- Service factor & margin adjustment
- NEMA application type guidance
- Input ampacity derating calculation
- Pump, fan, and compressor modes
Cable Sizing Calculator
Size conductors correctly using NEC ampacity tables — with voltage drop analysis, temperature correction, conduit fill derating, and copper vs. aluminum comparison built in.
- NEC 310 ampacity table lookup
- Voltage drop % per conductor run
- Copper vs. aluminum conductor comparison
- Temperature & conduit fill derating
- Recommended AWG / kcmil output
Single vs. 3-Phase Comparison
Compare single-phase and three-phase power systems side by side — calculate conductor savings, efficiency gains, and cost delta to make the right infrastructure decision for your facility.
- Power delivery capacity comparison
- Conductor material cost difference
- Efficiency & loss delta
- Load capacity per circuit type
- Upgrade cost-benefit analysis
Common Use Cases by Role
From field electricians to design engineers — here’s how each calculator maps to real job tasks.
| Role | Typical Task | Best Tool | Standard |
|---|---|---|---|
| Licensed Electrician | Size feeder conductors for a 200A commercial panel | Cable Sizing Calculator | NEC 310 |
| Electrical Engineer | Verify 3-phase current draw for motor load design | 3-Phase Power Calculator | IEEE 141 |
| Facility Manager | Evaluate single-to-three-phase upgrade ROI | Phase Comparison Tool | NEMA |
| Energy Consultant | Select correct VFD for HVAC fan motor retrofit | VFD Sizing Calculator | NEMA MG1 |
| Controls Engineer | Calculate voltage drop across long cable run | Cable Sizing Calculator | NEC 215 |
How to Use These Calculators
Get professional electrical results in under 60 seconds — no software, no spreadsheets.
Choose a Calculator
Pick from 3-phase power, VFD sizing, cable sizing, or phase comparison based on your task.
Enter Your Values
Input load (kW/HP), voltage, power factor, conductor length, or motor specs — all clearly labeled.
Get Instant Results
Results calculate in real time — amps, wire gauge, VFD HP, or system comparison output instantly.
Save or Share
Copy results, screenshot for job site reference, or share the tool link with your team.
Built for Real Electrical Work
These aren’t generic math tools — they reflect how electrical systems are actually designed, sized, and installed in the US.
NEC 2023 Compliant
Formulas align with the National Electrical Code — the standard used by US inspectors, AHJs, and contractors nationwide.
Real-Time Calculation
Results update as you type — no submit button, no page reload. Ideal for quick field checks on mobile.
Mobile-First Design
Designed for job site use on smartphones — large tap targets, readable fonts, and no zooming needed.
Always Free
No subscription, no credits, no paywall. Every tool is free to use as often as needed — forever.
Engineer-Validated
Each formula is reviewed by licensed electrical engineers — not just derived from textbooks or Wikipedia.
Context-Rich Inputs
Tooltips, defaults, and inline explanations make every field self-evident — no manual needed.
Ready to Run Your Calculations?
Join thousands of US engineers and electricians using Solvebility every month — free, fast, and code-compliant.
Frequently Asked Questions
Common questions from US electricians and engineers using these tools.
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