Free Electrical Tools
Professional electrical calculation tools for NEC compliance. All tools are free, accurate, and designed for electricians.
Box Fill CalculatorMost Popular
Calculate electrical box fill per NEC 314.16. The most accurate and easy-to-use box fill calculator online.
Wire Gauge Chart
Complete AWG wire gauge chart with conductor volume allowances per NEC Table 314.16(B).
NEC Code Reference
Quick reference guide for NEC 314.16 electrical box fill requirements and code sections.
Volume Converter
Convert between cubic inches and cubic centimeters for electrical box volume calculations.
Conduit Fill Calculator
Calculate conduit fill percentage per NEC Chapter 9. Supports EMT, IMC, RMC, and PVC conduit.
Pull Box Sizing vs Box Fill Guide
Separate NEC 314.16 box-fill volume from NEC 314.28 pull-box length, angle-pull, and U-pull sizing rules.
Voltage Drop and Box Fill Guide
Plan long branch circuits without missing NEC 314.16 box volume, conductor upsizing, device yokes, clamps, and grounding allowances.
Conductor Derating and Box Fill Guide
Separate NEC 310.15 ampacity derating from NEC 314.16 box-fill volume when conductor size or count changes.
Equipment Grounding Conductor Box Fill Guide
NEC 314.16(B)(5) examples for counting ground wires, bonding jumpers, pigtails, and mixed-size grounding conductors in boxes.
Surge Protective Device Box Fill Guide
Size SPD junction boxes with NEC 314.16, NEC 242, grounding, conductor length, internal clamps, and IEC surge-protection context.
GFCI Receptacle Box Fill Guide
NEC 314.16 examples for GFCI outlet boxes with line/load conductors, device yokes, pigtails, grounds, and clamps.
Device Yoke Box Fill Guide
Count switches, receptacles, dimmers, and other device yokes correctly under NEC 314.16(B)(4).
USB-C Receptacle Box Fill Guide
Size USB-C, USB-A, and combination receptacle boxes with NEC 314.16 device-yoke, grounding, clamp, and conductor-count examples.
Terminal Block Box Fill Guide
NEC 2023 examples for terminal blocks, conductor counts, grounding allowances, clamps, and practical box sizing.
Multi-Wire Branch Circuit Box Fill Guide
Count shared neutrals, handle ties, device yokes, pigtails, grounds, and large conductors in MWBC junction and device boxes.
Dishwasher and Disposal Box Fill Guide
NEC 314.16 examples for dishwasher junction boxes, disposal switch boxes, GFCI receptacles, grounds, clamps, and 12 AWG kitchen wiring.
Smart Switch Box Fill Guide
Worked NEC box-fill examples for smart switches, neutral bundles, travelers, pigtails, and deep electronic controls.
Motor Disconnect Box Fill Guide
Size motor disconnect, pump-control, and motor junction boxes with NEC 314.16, NEC 430, grounding, clamps, and IEC enclosure-space checks.
EV Charger Box Fill Guide
Worked box-fill examples for NEMA 14-50 outlets, hardwired EVSE wallboxes, 40 A and 60 A charging circuits, and outdoor charger junctions.
Wire Connector Box Fill Guide
NEC 314.16 examples for wire nuts, lever connectors, splice bundles, pigtails, and practical box volume.
Frequency Table Calculator
Quick electrical frequency table for 50 Hz, 60 Hz, generator output, VFD output, and field compatibility checks.
Box Fill Chart
Quick chart for common electrical box sizes, conductor-only capacity, and practical box choices before you run the exact NEC calculation.
Box Fill Calculator PDF
Download a printable NEC 314.16 worksheet PDF for field counts, rough-in notes, and final box-volume checks.
Ceiling Fan Box Fill Guide
Worked examples for fan-rated ceiling boxes, support fittings, and conductor counts under NEC 314.16 and NEC 314.27.
Bathroom Fan and Light Box Fill Guide
Size bathroom fan, light, timer, humidity-control, and heater switch boxes with NEC 314.16 conductor counts.
Aluminum Wire Box Fill Guide
Worked box-fill examples for aluminum branch circuits, receptacle repairs, feeder splices, and NEC 110.14 / 314.16 checks.
Weatherproof Box Fill Guide
Worked box-fill examples for outdoor GFCI receptacles, weatherproof switches, pump circuits, and wet-location junction boxes.
Extension Ring and Box Extender Fill Guide
Worked examples for listed extension rings, box extenders, mud rings, and when a bigger box is the only safe answer.
Neutral and Pigtail Box Fill Guide
Worked NEC 314.16 examples for neutrals, shared neutrals, pigtails, smart switches, and multi-gang device boxes.
Multi-Gang Switch Box Fill Guide
Worked box-fill examples for 2-gang and 3-gang switch boxes, dimmers, smart switches, and crowded remodel layouts.
Mini-Split Disconnect Guide
Box fill and enclosure sizing advice for mini-split disconnect-adjacent boxes, whip transitions, and upsized HVAC conductors.
Generator Inlet Guide
Box fill and enclosure sizing advice for portable generator inlet boxes, transfer-adjacent splices, and larger backup-power conductors.
Water Heater Guide
Box fill and enclosure sizing advice for storage water heaters, tankless circuits, disconnect-adjacent boxes, and larger branch-circuit conductors.
Range and Oven Junction Box Fill Guide
Size range, wall-oven, cooktop, and appliance junction boxes with NEC 314.16, 300.14, 422, 210.19(A)(3), and large-conductor examples.
Solar Disconnect Box Fill Guide
Worked box-fill examples for PV AC disconnects, rapid-shutdown junctions, inverter transitions, and upsized solar feeder conductors.
Essential Electrical Calculation Tools
Our suite of free electrical tools helps electricians, contractors, and engineers perform accurate calculations for NEC compliance.
Why Use Our Electrical Tools?
- NEC NEC Compliant: All calculations follow current National Electrical Code requirements
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- Regularly Updated: Updated for NEC 2023 including terminal block requirements