Calculate voltage drop, solve for minimum conductor size, or find the maximum run length — with an instant NEC 3%/5% verdict and the real energy cost of every volt you lose in the cable.
Voltage drop never travels alone. Size the conductor, check the ampacity, fill the conduit, price the copper, and verify the motor actually starts — one network of calculators.
Drop, %, end-of-run voltage and NEC verdict for any AC or DC circuit.
02Reverse-solve the minimum AWG or kcmil that meets your % limit and ampacity.
03How far can this gauge go before the drop exceeds your budget?
04Solar, RV, marine and battery wiring — 12, 24 and 48 volt systems.
05Automotive, RV and solar 12-volt runs where every tenth of a volt matters.
06208, 480 and 600 V feeders with the √3 factor and power factor built in.
07Panel → subpanel → load chains with cumulative drop per segment.
08NEC Table 310.16 with ambient temperature and bundling derates.
0940% rule for EMT with THHN conductor counts and minimum trade size.
10Gauge converter with diameter, area and resistance for every size.
11Price the watts your cable burns as heat, per year, at your kWh rate.
12Battery banks, telecom and off-grid systems at higher DC voltages.
13Audit every circuit in a panel at once and export the verdicts to CSV.
14Inrush at 6× running current — will it start, and what torque is left?
15NEMA MG-1 unbalance percentage with the motor derating curve.
16North American residential service, entered correctly — one leg, both legs, or a shared neutral.
17Drag the sliders, watch the wire change color and the bulb dim — voltage drop you can feel.
18400 A doesn't fit in one wire. Compare 2, 3 and 4 parallel sets by ampacity, drop and cost.
Resistance values come from NEC Chapter 9, Table 8 (DC resistance at 75 °C). AC results apply your power factor as an effective-impedance approximation; parallel sets divide the conductor resistance. Full formula reference →
Recommended maximum drop from panel to the farthest outlet — NEC 210.19(A), Informational Note No. 4.
Recommended maximum total drop from service equipment to the final outlet — NEC 215.2(A), Informational Note No. 2.
The NEC recommends keeping branch-circuit voltage drop under 3% and the combined feeder-plus-branch drop under 5%. For a 120 V circuit that means no more than 3.6 V lost in the branch wiring. Low-voltage DC systems (12/24/48 V) usually target 3% or less because every volt matters far more.
Current flows out to the load and back, so a single-phase or DC circuit has two conductors carrying current over your one-way distance. The factor of 2 in the formula accounts for that round trip; three-phase circuits use √3 instead.
Aluminum has roughly 61% higher resistance than copper at the same size, so an aluminum conductor typically needs to be about two AWG sizes larger to match copper's voltage drop. Aluminum wins on price and weight for large feeders.
Yes — the lost voltage becomes heat in the wire. Power lost equals the drop times the current (P = Vd × I). A 4% drop on a heavily loaded circuit can quietly burn tens of dollars of electricity a year, which is why this calculator prices the loss for you.
The NEC treats it as a performance recommendation, not a safety requirement — but excessive drop causes motor overheating, dim lighting, nuisance tripping and shortened equipment life. Ampacity, by contrast, is a hard safety limit this tool also checks.
DC resistance values for uncoated copper and aluminum conductors from NEC Chapter 9, Table 8 at 75 °C, with ampacities from Table 310.16. AC power factor is applied as an effective-impedance approximation suitable for typical branch and feeder work.