Does voltage drop matter for LED lights?

Yes — LEDs are more sensitive to voltage drop than incandescent bulbs. Most LED drivers have a minimum operating voltage. If voltage drops below the driver's minimum input (typically 108V for 120V-rated drivers), the LED may flicker, dim unevenly, or not turn on. For LED lighting circuits, keep voltage drop under 3% (ideally under 2%). Daisy-chained recessed LED lights at the end of a long run are most affected.

Is voltage drop different for AC and DC?

The basic formula is the same for DC and purely resistive AC loads. For AC circuits with significant inductance (motors, transformers), impedance replaces resistance, which slightly increases voltage drop. For most residential and light commercial AC circuits (lighting, outlets, small motors), the resistance-based formula is sufficiently accurate. For large motors and long industrial runs, use impedance-based calculations.

How far can I run 12 gauge wire at 20 amps?

At 120V with 3% max drop: 12 AWG copper at 20A can run about 47 feet one-way. At 15A: about 62 feet. At 10A: about 93 feet. At 240V, these distances double. To go further at 20A, upsize to 10 AWG (about 75 ft at 120V) or 8 AWG (about 118 ft). Our calculator gives exact distances for any combination of wire size, current, and voltage.

Voltage Drop Calculator — Free Wire Voltage Loss & Cable Size Estimator 2026 | AllInOneTools

⚡ Electrical & Energy

Voltage Drop Calculator

Calculate voltage loss in electrical wiring based on wire gauge, distance, current, and conductor type. Checks NEC 3% and 5% limits with wire upsizing recommendations.

Circuit Parameters

Wire Gauge (AWG)

Current (Load)

Amps

One-Way Distance

feet

System Voltage

Phase

Conductor

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Voltage Drop Details

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Wire Comparison

📝 Step-by-Step Calculation

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Voltage Drop Calculator: The Complete Guide to Wire Voltage Loss

Every electrical wire has resistance, and current flowing through resistance causes voltage loss — this is voltage drop. While small amounts are normal, excessive voltage drop causes dim lights, motor overheating, equipment malfunction, and wasted energy. The NEC recommends keeping voltage drop under 3% for branch circuits and 5% total for combined feeder and branch circuits.

The Voltage Drop Formula

Single-Phase: VD = 2 × L × I × R
Three-Phase: VD = √3 × L × I × R
Where:
  L = one-way length (feet)
  I = current (amps)
  R = wire resistance (Ω per foot)
VD% = (VD ÷ Source Voltage) × 100
Voltage at Load = Source Voltage − VD

Worked Example — 12 AWG, 100 ft, 20A at 120V

Wire: 12 AWG copper (R = 1.93 mΩ/ft)
VD = 2 × 100 × 20 × 0.00193 = 7.72V
VD% = 7.72 ÷ 120 × 100 = 6.4%
Voltage at load: 120 − 7.72 = 112.3V
⚠️ Exceeds 3% — upsize to 10 AWG:
VD = 2 × 100 × 20 × 0.00121 = 4.84V (4.0%)
Or 8 AWG: VD = 3.06V (2.5%) ✓

Voltage Drop by Wire Size

AWG	20A/100ft (120V)	20A/100ft (240V)	Max Distance at 3%*
14	12.3V (10.2%)	12.3V (5.1%)	29 ft
12	7.7V (6.4%)	7.7V (3.2%)	47 ft
10	4.8V (4.0%)	4.8V (2.0%)	75 ft
8	3.1V (2.5%)	3.1V (1.3%)	118 ft
6	2.0V (1.6%)	2.0V (0.8%)	184 ft

*Max one-way distance for 20A at 120V, copper, single-phase, 3% limit

Pro Tip — 240V Halves Voltage Drop Percentage

Running a circuit at 240V instead of 120V halves the percentage voltage drop for the same wire size and distance, because the same voltage drop in volts is a smaller percentage of the higher source voltage. This is why electric dryers, ranges, water heaters, and EV chargers use 240V — it allows smaller wire sizes for long runs. If voltage drop is a problem on a 120V circuit, consider whether the load can run on 240V.

Important — Voltage Drop Causes Real Problems

Excessive voltage drop is not just a code issue — it causes real operational problems. Motors running on low voltage draw more current (trying to maintain power), overheat, and fail prematurely. LED lights flicker or dim. Sensitive electronics malfunction. And all the "dropped" voltage converts to heat in the wire — wasted energy and potential fire risk. If you measure voltage at an outlet significantly below nominal, voltage drop in the wiring is likely the cause.

Frequently Asked Questions

How do you calculate voltage drop?▼

VD = 2 × Length × Current × Resistance/ft (single-phase). VD% = VD ÷ Voltage × 100. Keep under 3% for branches, 5% total. Example: 12 AWG, 100ft, 20A at 120V = 7.72V (6.4%). Use our calculator for instant results with any wire size.

What is acceptable voltage drop?▼

NEC recommends max 3% for branch circuits, 5% total (feeder + branch). Sensitive electronics: 2% or less. At 120V, 3% = 3.6V (load sees 116.4V). These are recommendations, not hard code requirements, but exceeding them causes operational problems.

How do I reduce voltage drop?▼

Use larger wire (most common fix). Shorten the run. Use higher voltage (240V halves %). Reduce load current. Going from 12 to 10 AWG reduces drop by ~37%. Going from 120V to 240V halves the percentage drop.

Does voltage drop matter for LEDs?▼

Yes — LEDs are more sensitive than incandescent. Most LED drivers need 108V minimum (at 120V nominal). Below that: flickering, dimming, or failure. Keep LED circuits under 3% (ideally 2%). End-of-run daisy-chained recessed LEDs are most affected.

How far can I run 12 gauge wire?▼

At 120V, 3% limit: 20A → 47 ft, 15A → 62 ft, 10A → 93 ft. At 240V: distances double. Beyond these, upsize to 10 AWG or larger. Use our calculator for exact distances at any current level.

Is voltage drop different for AC vs DC?▼

Basic formula is the same for DC and resistive AC loads. For AC loads with inductance (motors, transformers), impedance replaces resistance, slightly increasing drop. For most residential circuits, the resistance-based formula is accurate enough.

What causes voltage drop?▼

Wire resistance. All conductors have resistance — current × resistance = voltage loss (Ohm's Law). Longer runs, thinner wire, and higher current all increase drop. The lost voltage becomes heat in the wire — wasted energy and potential safety concern.