Electrical calculators for voltage drop, conduit fill, wire sizing, ampacity, and service-load estimates. Practical reference tools for electricians and contractors.
Calculate voltage drop on long runs and compare the result to common 3% and 5% design guidance values.
Verify NEC 40% fill rule for 1-2 conductors and 31-40% for 3+ conductors. Prevents overloading and damage.
Reference AWG sizes from #14 to 2000 MCM with ampacity ratings and physical dimensions for all conductor types.
NEC-based ampacity ratings accounting for insulation type, temperature conditions, and conductor grouping.
Cross-sectional areas and fill capacities for rigid, intermediate, and flexible conduit types.
Estimate service entrance size for residential, commercial, and industrial applications per NEC requirements.
The National Electrical Code (NEC) governs electrical installations in the United States, but real projects still depend on insulation ratings, terminal limits, equipment listings, local amendments, and the exact calculation method required by the job. These calculators are best used as planning and reference tools, not as substitutes for a full code review.
Voltage drop occurs when current flows through wire resistance over distance. The familiar 3% branch-circuit and 5% combined feeder-plus-branch values are common design guidance targets used to maintain performance. Excessive voltage drop reduces motor efficiency, causes lights to dim, and can damage appliances. A 240V circuit with 5% drop operates at only 228V.
Distance matters enormously. A 20-amp circuit on #14 copper wire can safely run only about 50 feet before hitting 3% drop. The same circuit on #8 wire extends to over 130 feet. Our voltage drop calculator instantly shows whether your wire size is adequate for your run distance.
The NEC 40% fill rule for 1-2 conductors and 31-40% for 3+ conductors prevents wire damage during installation and reduces heating from bundled conductors. Overstuffing conduit makes pulling wire difficult, can strip insulation, and creates dangerous heat buildup. A 1-inch conduit holds about 0.864 square inches of usable area—enough for two #8 THHN wires or six #12 THHN wires, but not both. Our calculator prevents these mistakes.
Wire size must match the circuit breaker protecting it and the actual load. A #12 wire rated at 20 amps needs a 20-amp breaker, never a 30-amp breaker. Oversized breakers don't protect undersized wire—they just allow dangerous overheating. Ampacity ratings depend on insulation type (THHN is rated higher than NM), temperature (90°C rated wire in a 60°C application), and how many wires bundle in the same conduit (derating applies). Professional electricians reference our ampacity charts daily to avoid costly mistakes.
Article 220 contains specific calculation methods for residential, commercial, and industrial services. Because those methods can vary by occupancy and load type, a simplified online calculator should be treated as an estimate until the full required method is applied. That still makes these tools useful for planning, budgeting, and early sizing decisions.
Equipment grounding conductors (EGC) must be the same size as circuit wires up to #6, then follow specific rules. Main bonding jumpers on services often require 0000 copper or 250 kcmil aluminum. Grounding electrode conductors running to rod or plate grounds must be sized by the service entrance conductor. These rules directly impact safety—poor grounding has caused fatal shocks and equipment damage. Our reference tools help you get grounding calculations right.
