Free Electrical Calculators | NEC Compliant Tools
Professional-grade electrical calculators built for electricians, engineers, and students. Instantly calculate conduit fill, voltage drop, and breaker sizing per NEC standards.
Conduit Fill Calculator
Calculate NEC-compliant conduit fill percentages. Select conduit type, size, and wire gauge to determine maximum conductor capacity.
Open CalculatorVoltage Drop Calculator
Determine voltage drop across wire runs. Input wire length, gauge, load amps, and voltage to ensure compliance with NEC recommendations.
Open CalculatorBreaker Size Calculator
Find the correct breaker and wire size for your circuit. Enter your load requirements and let the calculator match NEC ampacity tables.
Open CalculatorElectrical calculations made simple.
Electrical work demands precision. Whether you're sizing a conduit run for a commercial buildout or verifying voltage drop on a long residential feeder, accurate calculations are the difference between a safe installation and a code violation. Our suite of conduit fill, voltage drop, and breaker sizing calculators gives you instant, NEC-referenced answers.
Every calculator is built around the National Electrical Code tables that professional electricians rely on daily. We surface the math transparently — you see the wire areas, fill percentages, resistance values, and ampacity ratings behind every result. No black boxes, no hidden assumptions. Just the numbers you need to plan, bid, and install with confidence.
These tools are designed for journeyman electricians studying for their license, electrical engineering students learning NEC fundamentals, and seasoned contractors who want a quick cross-check in the field. Each calculator runs entirely in your browser — no data is collected, no account required. Bookmark the page and use it whenever you need a fast, reliable reference.
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Frequently Asked Questions
A conduit fill calculator helps electricians determine how many wires of specific sizes can safely fit inside a conduit. The NEC (National Electrical Code) sets maximum fill percentages — typically 40% for three or more conductors — to ensure wires can be pulled through without damage and to prevent excessive heat buildup.
Voltage drop occurs when electrical current flows through a conductor, causing a reduction in voltage at the load end. Excessive voltage drop can lead to underperforming equipment, flickering lights, and potential damage to sensitive electronics. The NEC recommends keeping voltage drop below 3% for branch circuits and 5% total for feeders and branch circuits combined.
Breaker sizing depends on the wire gauge, the load being served, and NEC requirements. The breaker must protect the wire from overheating — its amperage rating should match or be slightly below the wire's ampacity. For continuous loads (running 3+ hours), the breaker must be sized at 125% of the load current.
Our calculators reference NEC tables and standards as educational tools. While we strive for accuracy based on current NEC editions, always verify results with the specific code edition adopted in your jurisdiction. Local amendments may apply, and a licensed electrician should review all calculations for actual installations.
These calculators are designed as educational and reference tools for both residential and commercial calculations. However, commercial projects often have additional requirements such as demand factors, derating for ambient temperature, and specific conduit fill considerations. Professional electricians and engineers should use these as a starting point and verify against project-specific requirements.