NEC electrical calculators
built for the field

Voltage Drop Calculator

Single- and three-phase AC drop. K-factor under #2 AWG, NEC Table 9 for #2 and larger. Flags the 3% and 5% NEC recommendations.

DC Voltage Drop Calculator

DC circuits (solar, battery banks, marine) using NEC Chapter 9, Table 8 resistance values.

Solar Voltage Drop Calculator

PV DC string and array conductors against the 2% and 3% solar design targets. Reports power loss; NEC Chapter 9, Table 8 resistance.

3-Phase Voltage Drop Calculator

Three-phase voltage drop using the √3 multiplier. NEC Table 9 AC resistance, same method as the main VD tool.

12V Voltage Drop Calculator

Automotive, RV, and battery systems. Defaults to 12V; override for 24V and 48V banks.

Extension Cord Voltage Drop

Match a cord gauge (16-10 AWG) to a tool load. Practical 3% guideline; K-factor method.

Marine Voltage Drop Calculator

Boat wiring per ABYC E-11: K = 10.75 copper formula, 3% critical and 10% non-critical limits, marine cable sizes 18 AWG to 4/0.

Voltage Drop Chart

Printable max-run-distance tables at the 3% recommendation, for 120V and 240V, copper and aluminum, by AWG and load.

Wire Size Calculator

Returns the minimum conductor for a load, distance, and target voltage drop. Checks NEC Table 310.16 ampacity, derating, and standard OCPD sizes.

Wire Gauge Calculator

Enter a required ampacity, get the minimum AWG. NEC Table 310.16 with full derating: ambient, conductor count, and 110.14(C) termination cap.

Wire Ampacity Calculator

Derated ampacity per NEC 310.15: ambient correction, conductor-count adjustment, and 110.14(C) termination cap.

Wire Ampacity Chart

Printable NEC Table 310.16 base ampacities for copper and aluminum, 60/75/90C columns, 18 AWG to 2000 kcmil. Computed from the audited ampacity calculator.

DC Wire Size Calculator

Sizes conductors for solar PV, battery banks, and 12/24/48V systems. Table 8 DC-resistance voltage drop plus Table 310.16 derated ampacity.

AWG Calculator

AWG/kcmil ↔ mm² conversions from the published NEC Chapter 9 Table 8 areas, with the IEC 60228 metric cross-reference.

Cable Size Calculator

Sizes each conductor of a multi-conductor cable when more than three current-carrying conductors are bundled, applying the NEC Table 310.15(C)(1) adjustment on top of Table 310.16 ampacity.

Dwelling Service Conductor Calculator

Minimum copper and aluminum service or feeder conductor for a 100 to 400 amp single-phase dwelling under the NEC 310.12 83% allowance, with the standard Table 310.16 size for comparison.

Ampacity Correction & Adjustment Calculator

Reads the NEC Table 310.15(B)(1) ambient temperature correction factor and Table 310.15(C)(1) conductor-count adjustment for a conductor, then reports the derated ampacity.

Parallel Conductor Sizing Calculator

Total ampacity of conductors run in parallel under NEC 310.10(G): the 1/0 minimum, per-conductor ampacity times the number of sets, the shared-raceway Table 310.15(C)(1) derating, and the 250.122(F) grounding conductor per raceway.

Conduit Fill Calculator

Mixed conductors in EMT, RMC, IMC, or PVC against the 53% / 31% / 40% limits in NEC Chapter 9, Table 1.

Conduit Size Calculator

Minimum conduit trade size for your conductor bundle across EMT, RMC, IMC, and PVC Schedule 40/80, all in one comparison table.

Cable Tray Fill Calculator

Multiconductor cable fill for ladder and ventilated trough trays per NEC Table 392.22(A), Columns 1 and 2, with the minimum standard tray width.

Wireway Fill Calculator

Conductor fill for metal and nonmetallic wireways against the NEC 376.22(A) / 378.22 20% limit, minimum standard size, and the over-30-conductor adjustment flag.

EMT Conduit Fill Calculator

Fill calculation locked to EMT. Minimum trade size and actual fill percentage for your conductor bundle.

PVC Conduit Fill Calculator

PVC Schedule 40 and Schedule 80 fill per NEC Chapter 9. Separate Table 4 areas applied for each schedule.

Conduit Fill Table

Max same-size conductor counts from NEC 2020 Annex C: EMT, IMC, RMC, PVC Sch 40/80. THHN/THWN-2 and XHHW-2. Printable.

PVC Conduit Expansion Calculator

Thermal length change of a straight PVC conduit run from the temperature swing per NEC Table 352.44, with the 1/4 inch expansion-fitting threshold and an optional direct-sunlight allowance.

Conduit Support Spacing Calculator

Maximum support spacing for PVC, RMC, EMT, FMC, and LFMC by trade size per NEC 352.30/344.30/358.30/348.30/350.30, with the box-securing distance and a support-point count for your run.

RTRC Conduit Expansion Calculator

Thermal length change of a straight RTRC (fiberglass) conduit run from the temperature swing per NEC Table 355.44, with the 1/4 inch expansion-fitting threshold and an optional direct-sunlight allowance.

Box Fill Calculator

Required outlet, switch, or junction box volume per NEC 314.16(B): conductor, clamp, support-fitting, device-yoke, and grounding allowances against the box capacity.

Pull Box Size Calculator

Minimum pull and junction box dimensions per NEC 314.28(A): straight pulls at 8x the largest raceway and angle or U pulls at 6x plus the row sum, for conductors 4 AWG and larger.

Breaker Size Calculator

Standard NEC 240.6(A) breaker for a load with the 125% continuous rule, plus the minimum conductor the breaker can legally protect.

Fuse Size Calculator

Standard NEC 240.6(A) fuse for a general-use load, including the fuse-only 1/3/6/10/601 A ratings, with the 125% continuous rule and the minimum conductor per 240.4(B)/(D).

Motor Breaker Sizing Calculator

Motor branch-circuit breaker or fuse per NEC Article 430: full-load current from Table 430.250, Table 430.52 device percentages, and the 430.22 conductor.

GFCI Breaker Sizing Calculator

Check whether NEC 2020 210.8 requires GFCI protection for a location, then size the GFCI breaker and conductor with the 1-pole or 2-pole call.

EV Charger Circuit Calculator

Branch-circuit breaker and wire for an EV charger: NEC Article 625 continuous-load rule sizes the circuit at 125% of the charger rating, with SAE J1772 Level 1/2 presets.

Transformer Sizing Calculator

Maximum primary and secondary overcurrent device for a transformer 1000V or less per NEC Table 450.3(B): rated current from kVA and the 125/167/250/300% limits.

MCA & MOCP Calculator

HVAC minimum circuit ampacity and maximum overcurrent protection per NEC Article 440: 125% conductor (440.33), 175%/225% device (440.22), and the Table 310.16 wire size.

Motor Overload Protection Calculator

Running-overload relay for a motor per NEC 430.32: 125% or 115% of nameplate full-load current, with the 430.32(C) increase to 140% or 130%.

Motor & HVAC Disconnect Sizing Calculator

Minimum disconnect ampere rating for a motor (NEC 430.110) or an A/C compressor (NEC 440.12): 115% of the table full-load current, or of the greater of RLA or BCSC.

Motor Full-Load Current Calculator

Look up motor full-load current from NEC Table 430.248/430.250 by horsepower and voltage (430.6(A)(1)), with the 430.22 branch-circuit conductor minimum ampacity.

Multi-Motor Feeder Calculator

Size a feeder for a group of motors per NEC 430.24 (125% of the largest motor FLC plus the other motors) and 430.62(A) (largest branch device plus the other FLCs, rounded down).

Feeder Tap Conductor Size Calculator

Size a feeder tap conductor under the NEC 240.21(B) 10-foot and 25-foot tap rules: required ampacity (1/10 or 1/3 of the feeder OCPD) and the smallest Table 310.16 conductor.

Generator Conductor Size Calculator

Size generator output conductors under the NEC 445.13(A) 115%-of-nameplate rule: nameplate current from kVA and the smallest Table 310.16 copper or aluminum wire.

Welder Circuit Calculator

Size a single arc welder branch circuit per NEC Article 630: the Table 630.11(A) duty-cycle-adjusted conductor from Table 310.16 and the 630.12 200% overcurrent device.

Capacitor Conductor & OCPD Calculator

Size power-capacitor circuit conductors per NEC 460.8(A): 135% of the rated capacitor current (from kVAR or entered directly) and the smallest Table 310.16 copper or aluminum wire.

Water Heater Circuit Calculator

Size an electric water heater branch circuit per NEC 422.13: the 125% continuous-load minimum breaker and conductor, plus the 422.11(E) 150% breaker maximum window.

Electrical Load Calculator

Dwelling service load per NEC 220.82 (optional method): floor area, appliances, and HVAC in; calculated amps and standard service size out.

Existing Dwelling Load Calculator

Existing dwelling addition per NEC 220.83: check whether an existing service can carry an added load, with the 8 kVA/40% split and the 220.60 noncoincident larger-of-HVAC rule.

Existing Load by Metered Demand Calculator

Existing load from measured demand per NEC 220.87: recorded maximum demand at 125% plus the new load, checked against the feeder ampacity or service rating, with the spare-capacity figure.

Multifamily Dwelling Load Calculator

Apartment building feeder and service load per the NEC 220.84 optional method: per-unit connected load at 100% nameplate, the Table 220.84 demand factor by unit count, and house loads added after.

Residential Electrical Load Calculator

Dwelling service load by the NEC Article 220 standard method: category-by-category demand factors (Tables 220.42/220.54/220.55, noncoincident HVAC, largest-motor adder).

Commercial Load Calculator

Non-dwelling load per NEC 220 Part III: general lighting by occupancy (Table 220.12), receptacle, kitchen, and show-window loads to a service size.

Service Size Calculator

From a known load: minimum service disconnect (NEC 230.79), service-entrance conductor (230.42, Table 310.16), and grounding electrode conductor (Table 250.66) with the 250.66(A)/(B) caps.

Range / Cooktop Demand Load Calculator

Household cooking demand per NEC Table 220.55 Column C: one or more identical ranges, the Note 1 step over 12 kW, and the Note 4 branch-circuit cases for ranges, ovens, and cooktops.

Electric Dryer Demand Load Calculator

Household electric clothes dryer demand per NEC 220.54: the 5000 VA (or nameplate) per-dryer minimum and the Table 220.54 multi-dryer demand factors, with demand amps at 240 V.

Commercial Kitchen Equipment Demand Calculator

Commercial kitchen equipment demand per NEC Table 220.56: the demand factor by unit count plus the two-largest-loads floor made explicit, with demand kVA, kW, and amps.

Commercial Receptacle Load Calculator

Non-dwelling receptacle load per NEC 220.14(I) and Table 220.44: 180 VA per strap, first 10 kVA at 100% and the rest at 50%, plus the 220.14(K) office 1 VA/ft² floor.

Neutral Load Calculator

Feeder and service neutral load per NEC 220.61: the maximum unbalance with the range and dryer 70% reduction, the over-200 A 70% demand factor, and the nonlinear no-reduction rule.

Minimum Branch Circuits Calculator

Minimum dwelling branch circuits per NEC 210.11: general-purpose circuits from the 3 VA/ft² general lighting load plus the required small-appliance, laundry, bathroom, and garage circuits.

Show Window & Sign Lighting Load Calculator

Show-window and sign loads per NEC 220.43(A)/220.14(G) and 220.14(F): 200 VA per linear foot of show window plus 1200 VA per required sign circuit, with the 125% continuous figure and amps.

Multi-Outlet Assembly Load Calculator

Fixed multioutlet assembly load per NEC 220.14(H): 180 VA per 5 ft where appliances are unlikely to run at once, or per 1 ft where likely, with the connected load and amps.

Track Lighting Load Calculator

Track lighting load per NEC 220.43(B): 150 VA per 2 ft of lighting track (or fraction thereof) at 100% in other-than-dwelling occupancies, with the 125% continuous figure and amps.

Equipment Grounding Conductor Size Calculator

Minimum equipment grounding conductor from the OCPD rating per NEC Table 250.122, with the 250.122(B) proportional upsize for voltage-drop conductors and the 250.122(F) parallel-raceway rule.

Grounding Electrode Conductor Size Calculator

Minimum grounding electrode conductor from the service conductor size per NEC Table 250.66, with the 250.66(A) ground-rod and 250.66(B) concrete-encased caps and parallel equivalent-area handling.

Bonding Jumper Size Calculator

Minimum main, system, or supply-side bonding jumper and grounded conductor from the phase conductor per NEC Table 250.102(C)(1), including the Note 1 12.5% rule above 1100 kcmil and parallel equivalent-area handling.

Solar PV Wire Size Calculator

PV source and output circuit conductors and fuses per NEC 690.8 and 690.9: 125% maximum current from Isc, the larger of the two 690.8(B) paths on Table 310.16, and the standard OCPD rating.

Solar 120% Rule Calculator

Load-side PV and storage interconnection per NEC 705.12(B)(3): the sum method and the 120% rule tested from 125% of the source output current, with the maximum source and largest standard backfed OCPD a busbar allows.