ElectricalIntermediateConductors and Circuits

Voltage-Drop Calculator

Estimate single-phase or balanced three-phase voltage drop using a transparent conductor reference, resistance-only estimate, or project-specific AC impedance data.

Why it matters: Excessive drop can impair starting, controls, lighting, and equipment performance even when ampacity is adequate.

User inputs

Enter field measurements

13 inputs

Choose the conductor-data methodSelections update the active engineering inputs.

Unit systemSelect the unit convention used for all values in this calculation.

Circuit typeSelect single-phase/two-wire or balanced three-phase.

Source voltage (Vs)VNominal or measured source voltage.

Load current (I)AExpected or measured load current.

One-way circuit length (L)ft or mOne-way length from source to load in the selected unit system.

Parallel conductor sets (n)sets/phaseNumber of identical conductors or cable sets in parallel per phase.

Conductor materialGeneric conductivity basis used only by the two estimated-data methods.

Conductor sizeSelect the conductor cross-sectional area used for the resistance estimate.

Conductor temperature (Tc)°CEstimated operating conductor temperature used to adjust resistance from its 20°C reference value.

Installation / racewaySelect the visible reactance screening assumption. Use the manufacturer-data tab when project values are available.

Displacement power factor (PF)0–1Use displacement power factor for the impedance-angle calculation.

Reactive directionLagging adds the X sin φ term; leading subtracts it.

Project screening limit (ΔVlimit)%Enter the project-specific review criterion; the calculator does not impose a code limit.

Calculated result

Engineering evaluation

Within entered screening limit

Estimated voltage drop (ΔV)5.38 V

Voltage drop (ΔV%): 1.12 %
Estimated load voltage (VL): 475 V
Conductor resistance used (Rc): 0.12 Ω/1,000 ft
Conductor reactance used (Xc): 0.05 Ω/1,000 ft
Parallel conductor sets (n): 1 sets/phase
Conductor area (Acond): 53.48 mm²
Circuit multiplier (k): 1.732
Power factor (PF): 0.9
Effective R cos φ component (Reff cos φ): 0.108 Ω/1,000 ft
Lagging effective X sin φ component (Xeff sin φ): 0.022 Ω/1,000 ft
Entered screening limit (ΔVlimit): 3 %

Engineering interpretation

Estimated load voltage is 475 V, a 1.12% change from the entered source voltage. The calculation used the conductor reference method with 1 parallel set per phase. The 3% comparison is a user-entered screening criterion, not conductor-selection or code-compliance certification.

Important limitations

Estimated conductor data is a transparent screening basis, not an electrical-code table or manufacturer product value. Confirm stranding, material, temperature, frequency, cable geometry, raceway, and installed impedance before final design.
The equation assumes a balanced sinusoidal circuit and user-entered conductor impedance at the applicable frequency and temperature. Harmonics, parallel-path current sharing, and connection resistance require separate evaluation.

Engineering knowledge center

Understand the calculation—not just the answer

2026-08-08 · Enhanced review build

Circuit voltage-drop equation

ΔV = \frac{\sqrt{3} I L (R_{c} \cos φ + X_{c} \sin φ)}{1000 n}

Percent voltage drop

ΔV % = \frac{ΔV}{V_{s}} \times 100

Estimated load voltage

V_{L} = V_{s} - ΔV

Conductor-data relationship

R_{c} (T_{c}) = ρ_{20} \frac{1000}{A_{cond}} [1 + α_{20} (T_{c} - 20)]

Current substitution

ΔV = 1.732 × 80 × 300 ft × [(0.11951 ÷ 1) × 0.9 + (0.05 ÷ 1) × 0.43589] Ω/1,000 ft / 1000 = 5.38 V; ΔV% = 1.12%.

Calculation sequence

Step-by-step method

Derive conductor resistance from material, area Acond, and entered temperature Tc; use the selected visible reactance assumption.
Divide single-conductor resistance and reactance by the number of equal parallel sets per phase.
Resolve effective impedance along the load-current angle using Reff cos φ and Xeff sin φ; subtract the reactive term for a leading load.
Apply the balanced three-phase circuit multiplier.
Divide calculated drop by source voltage and compare it only with the user-entered screening limit.

Equation legend

Inputs and calculated quantities

Vs: Source voltage — V
I: Load current — A
L: One-way circuit length — ft or m
n: Parallel conductor sets — sets/phase
Tc: Conductor temperature — °C
PF: Displacement power factor — 0–1
ΔVlimit: Project screening limit — %
ΔV: Estimated voltage drop — V
ΔV%: Voltage drop — %
VL: Estimated load voltage — V
Rc: Conductor resistance used — Ω/1,000 ft
Xc: Conductor reactance used — Ω/1,000 ft
n: Parallel conductor sets — sets/phase
Acond: Conductor area — mm²
k: Circuit multiplier
PF: Power factor
Reff cos φ: Effective R cos φ component — Ω/1,000 ft
Xeff sin φ: Lagging effective X sin φ component — Ω/1,000 ft
ΔVlimit: Entered screening limit — %

Conductor reference library

Transparent values—not reproduced code tables

The reference method derives resistance from conductor cross-sectional area, a stated material resistivity, and the entered temperature. The reactance choices are visible screening assumptions. For final work, replace them with the applicable manufacturer, project, measured, or legally adopted code data.

Common conductor areas and calculated resistance at 75°C
Conductor size	Area	Area	Copper R₇₅	Aluminum R₇₅
14 AWG	2.081 mm²	4.107 kcmil	3.0712 Ω/1,000 ft	5.0576 Ω/1,000 ft
12 AWG	3.309 mm²	6.53 kcmil	1.9315 Ω/1,000 ft	3.1807 Ω/1,000 ft
10 AWG	5.261 mm²	10.38 kcmil	1.2147 Ω/1,000 ft	2.0004 Ω/1,000 ft
8 AWG	8.367 mm²	16.51 kcmil	0.7638 Ω/1,000 ft	1.2579 Ω/1,000 ft
6 AWG	13.301 mm²	26.25 kcmil	0.4805 Ω/1,000 ft	0.7912 Ω/1,000 ft
4 AWG	21.151 mm²	41.74 kcmil	0.3022 Ω/1,000 ft	0.4976 Ω/1,000 ft
3 AWG	26.67 mm²	52.63 kcmil	0.2396 Ω/1,000 ft	0.3946 Ω/1,000 ft
2 AWG	33.631 mm²	66.37 kcmil	0.1900 Ω/1,000 ft	0.3129 Ω/1,000 ft
1 AWG	42.407 mm²	83.69 kcmil	0.1507 Ω/1,000 ft	0.2482 Ω/1,000 ft
1/0 AWG	53.475 mm²	105.6 kcmil	0.1195 Ω/1,000 ft	0.1968 Ω/1,000 ft
2/0 AWG	67.431 mm²	133.1 kcmil	0.0948 Ω/1,000 ft	0.1561 Ω/1,000 ft
3/0 AWG	85.029 mm²	167.8 kcmil	0.0752 Ω/1,000 ft	0.1238 Ω/1,000 ft
4/0 AWG	107.219 mm²	211.6 kcmil	0.0596 Ω/1,000 ft	0.0982 Ω/1,000 ft
250 kcmil	126.677 mm²	250 kcmil	0.0505 Ω/1,000 ft	0.0831 Ω/1,000 ft
300 kcmil	152.012 mm²	300 kcmil	0.0420 Ω/1,000 ft	0.0692 Ω/1,000 ft
350 kcmil	177.348 mm²	350 kcmil	0.0360 Ω/1,000 ft	0.0593 Ω/1,000 ft
400 kcmil	202.683 mm²	400 kcmil	0.0315 Ω/1,000 ft	0.0519 Ω/1,000 ft
500 kcmil	253.354 mm²	500 kcmil	0.0252 Ω/1,000 ft	0.0415 Ω/1,000 ft
600 kcmil	304.025 mm²	600 kcmil	0.0210 Ω/1,000 ft	0.0346 Ω/1,000 ft
750 kcmil	380.031 mm²	750 kcmil	0.0168 Ω/1,000 ft	0.0277 Ω/1,000 ft
1,000 kcmil	506.708 mm²	1,000 kcmil	0.0126 Ω/1,000 ft	0.0208 Ω/1,000 ft

Visible installation-reactance screening assumptions
Installation selection	X assumption	Intended use
Cable / closely grouped conductors	0.040 Ω/1,000 ft	Low-reactance screening assumption for closely grouped conductors.
PVC or nonmagnetic raceway	0.050 Ω/1,000 ft	General screening assumption for conductors in a nonmagnetic raceway.
Steel raceway	0.070 Ω/1,000 ft	Higher-reactance screening assumption; raceway geometry and conductor arrangement remain important.

What material changes

Material resistivity controls the calculated resistance. Aluminum generally needs more conductor area than copper for the same resistance target.

What temperature changes

Conductor resistance rises with temperature. The estimate applies a visible linear temperature correction from the 20°C reference.

What raceway changes

Raceway material and conductor geometry influence reactance. The listed X values are screening assumptions, not product or code values.

What this does not select

Voltage drop alone does not establish ampacity, insulation rating, terminal limits, overcurrent protection, fault duty, grounding, or code compliance.

Technical basis

References and source standards

Schneider Electric—Busway Systems Catalog 5600CT9101Page 42, Voltage Drop Sample Calculations: ΔV = √3 I(R cos φ + X sin φ), including worked 50% power-factor examples.
ABB—Electrical Installation Handbook, Vol. 2Section 2.2, page 57, Eq. (1): single- and three-phase conductor voltage drop using resistance, reactance, power factor, length, and parallel conductors.
NIST Circular 31—Copper Wire TablesPublic reference for AWG dimensions, circular-mil area, copper resistivity, resistance, and temperature relationships.
Copper Development Association—Recommended Practices for Designing and Installing Copper Building Wire SystemsSection 5.3 discusses conductor size, length, temperature, and the resistance-temperature relationship used in voltage-drop evaluation.
NFPA 70, National Electrical CodeThe legally adopted edition and local amendments govern final work; no protected conductor or voltage-drop tables are reproduced.

Engineering calculation disclaimer

These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.

Read the full use and limitation statement

Voltage-Drop Calculator

Enter field measurements

Engineering evaluation

Engineering interpretation

Important limitations

Understand the calculation—not just the answer

Step-by-step method

Inputs and calculated quantities

How this calculation is used

Building design

Construction

Commissioning

Assumptions and limitations

Assumptions

Limitations

Verification procedure

Common engineering mistakes

Transparent values—not reproduced code tables

What material changes

What temperature changes

What raceway changes

What this does not select

References and source standards

Engineering calculation disclaimer

Voltage-Drop Calculator

Enter field measurements

Engineering evaluation

Engineering interpretation

Important limitations

Understand the calculation—not just the answer

Step-by-step method

Inputs and calculated quantities

How this calculation is used

Building design

Construction

Commissioning

Assumptions and limitations

Assumptions

Limitations

Verification procedure

Common engineering mistakes

Transparent values—not reproduced code tables

What material changes

What temperature changes

What raceway changes

What this does not select

References and source standards

Related calculators

Engineering calculation disclaimer