Source voltage in volts; presets do not select phase.
Enter any supported custom voltage directly.
Single-phase / two-wire resistive model; balanced three-phase resistive model. Phase is selected independently of voltage.
Positive decimal current in amperes. No ampacity or breaker inference.
Enter source-to-load distance once. The engine applies 2 or √3 internally.
Unit changes preserve physical distance.
100% IACS standard annealed copper
User-selected design target, greater than 0% and less than 100%. These presets are not code limits.
Enter a custom target directly.
Enter the conductor size you already selected from your ampacity/code/design process. This calculator can then show whether voltage-drop considerations would move you to a larger supported size.
Baseline refers to the selected material. Material comparison shows independent voltage-drop minima; it does not transfer an ampacity selection between materials. An entered baseline is never downsized.
Resistance model referenced at 20 °C using nominal conductor area. Warmer conductors generally have higher resistance. Actual cable construction and operating conditions can change voltage drop.
Software bounds: positive voltage/current ≤1,000,000 V/A; one-way distance ≤10,000,000 ft. Minimum positive value is 0.000001 in normalized units. These are software limits, not electrical requirements.
Smallest supported conductor meeting your selected 3% voltage-drop target under this calculator’s resistance model.
3 AWG estimates 2.46% drop and is the first supported size within your selected 3% target. The next smaller supported 4 AWG estimates 3.11%, above the target based on the unrounded value.
Resistance model referenced at 20 °C using nominal conductor area. Warmer conductors generally have higher resistance. Actual cable construction and operating conditions can change voltage drop.
Electrical note: This calculator estimates voltage drop only. It does not determine conductor ampacity, breaker/fuse size, terminal temperature rating, installation method, grounding/bonding, conduit requirements, or code compliance.
Verify applicable electrical requirements, equipment ratings and installation conditions before installation.
Actual AC voltage drop can also depend on conductor reactance, power factor, wiring method, frequency, conductor temperature, and installation conditions. This calculator uses the documented resistive model shown in the methodology.
Estimated voltage at load assumes the source remains at the entered nominal voltage; source sag, transformer regulation and upstream conductor drop are not modeled.
Ordered by nominal area, not label. Target decisions use unrounded percentages; a displayed value equal to the target can still exceed it before rounding.
| Conductor | Drop V | Drop % | Estimated load V | Target status |
|---|---|---|---|---|
| 6 AWG | 11.85 | 4.94% | 228.15 | Exceeds target |
| 4 AWG | 7.45 | 3.11% | 232.55 | Exceeds target |
| 3 AWG — selected/checked — smallest supported meeting target | 5.91 | 2.46% | 234.09 | Within target |
| 2 AWG | 4.69 | 1.95% | 235.31 | Within target |
| 1 AWG | 3.72 | 1.55% | 236.28 | Within target |
Nominal-area, straight-conductor resistive model at 20 °C. R per 1000 ft = K × 1000 / area in circular mils; K is 10.371 for standard annealed copper and 17.002 for EC-H19 aluminum, in Ω·cmil/ft. No strand-lay, coating, operating-temperature or AC-impedance corrections.
100% IACS standard annealed copper
Voltage Drop Wire Size Calculator Mode: Find Wire Size System voltage: 240 V Single-phase (two-wire resistive model) Load current: 60 A One-way distance: 250 ft; 250 ft Material: Copper; 100% IACS standard annealed copper Selected voltage-drop target: 3% (user-selected design target) Nominal-area, straight-conductor resistive model at 20 °C. R per 1000 ft = K × 1000 / area in circular mils; K is 10.371 for standard annealed copper and 17.002 for EC-H19 aluminum, in Ω·cmil/ft. No strand-lay, coating, operating-temperature or AC-impedance corrections. Resistance model referenced at 20 °C using nominal conductor area. Warmer conductors generally have higher resistance. Actual cable construction and operating conditions can change voltage drop. Smallest supported voltage-drop conductor: 3 AWG Copper: 5.91 V drop; 2.46%; estimated load 234.09 V; Within selected voltage-drop target; resistance 0.19704 Ω/1000 ft at 20 °C Retained/voltage-drop conductor: 3 AWG Copper: 5.91 V drop; 2.46%; estimated load 234.09 V; Within selected voltage-drop target; resistance 0.19704 Ω/1000 ft at 20 °C 3 AWG estimates 2.46% drop and is the first supported size within your selected 3% target. The next smaller supported 4 AWG estimates 3.11%, above the target based on the unrounded value. Nearby-size matrix 6 AWG Copper: 11.85 V drop; 4.94%; estimated load 228.15 V; Exceeds selected voltage-drop target; resistance 0.39507 Ω/1000 ft at 20 °C 4 AWG Copper: 7.45 V drop; 3.11%; estimated load 232.55 V; Exceeds selected voltage-drop target; resistance 0.24846 Ω/1000 ft at 20 °C 3 AWG Copper: 5.91 V drop; 2.46%; estimated load 234.09 V; Within selected voltage-drop target; resistance 0.19704 Ω/1000 ft at 20 °C 2 AWG Copper: 4.69 V drop; 1.95%; estimated load 235.31 V; Within selected voltage-drop target; resistance 0.15626 Ω/1000 ft at 20 °C 1 AWG Copper: 3.72 V drop; 1.55%; estimated load 236.28 V; Within selected voltage-drop target; resistance 0.12392 Ω/1000 ft at 20 °C One-way distance = 250 ft (76.2 m) Conductor resistance at 20 °C = 0.19704 Ω / 1000 ft; 0.64645 Ω/km Round-trip resistive path = 2 × 250 = 500 ft; R_total = 0.098518 Ω Vdrop = 2 × I × R_per_1000ft × L_ft / 1000 = 5.9111 V dropPct = Vdrop / systemVoltage × 100 = 2.463% Estimated voltage at load = systemVoltage − Vdrop = 234.09 V This checks voltage drop only. It does not determine whether the conductor has sufficient ampacity or meets installation requirements. Actual AC voltage drop can also depend on conductor reactance, power factor, wiring method, frequency, conductor temperature, and installation conditions. This calculator uses the documented resistive model shown in the methodology. Estimated voltage at load assumes the source remains at the entered nominal voltage; source sag, transformer regulation and upstream conductor drop are not modeled. Electrical note: This calculator estimates voltage drop only. It does not determine conductor ampacity, breaker/fuse size, terminal temperature rating, installation method, grounding/bonding, conduit requirements, or code compliance. Verify applicable electrical requirements, equipment ratings and installation conditions before installation. NIST/NBS Handbook 100: Copper Wire Tables (pp. 3, 6; PDF pages 9, 12): https://nvlpubs.nist.gov/nistpubs/Legacy/hb/nbshandbook100.pdf NIST/NBS Handbook 109: Aluminum Wire Tables (p. 1; PDF page 9): https://nvlpubs.nist.gov/nistpubs/Legacy/hb/nbshandbook109.pdf Schneider Electric: Calculation of voltage drop in steady load conditions: https://www.electrical-installation.org/enwiki/Calculation_of_voltage_drop_in_steady_load_conditions NIST Guide to the SI: length conversions: https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8
Estimate voltage drop for long runs, find the smallest supported conductor meeting your selected drop target, and understand a user-entered baseline upsize.
Choose Find Wire Size, Check Wire Size or Compare Materials. Enter system voltage, phase, load current, one-way conductor distance and your selected maximum voltage-drop percentage. Voltage presets never infer phase. Enter custom voltage and target values directly. Choose Copper or Aluminum, or compare both with identical electrical inputs.
The optional Advanced baseline is a conductor already selected by you through a separate ampacity/code/design process. This calculator never derives that baseline from current and never recommends downsizing it. Change ft/m without changing physical distance. Copy Voltage Drop Results and browser Print / Save PDF include inputs, method, results, comparisons and formulas. Reset restores the default fixture, Find mode and blank baseline.
Voltage drop is the estimated reduction in voltage along a conductor carrying current. In this resistance-only model, current multiplied by resistance gives the voltage change. Conductor area, material and distance affect resistance; this model does not represent every AC installation.
The voltage-drop conductor is the smallest supported size within your user-selected target under the stated model. It is a voltage-drop comparison, not a complete installation design.
Single-phase / two-wire resistive model: Vdrop = 2 × I × R_per_length × L. Here I is load current, R_per_length is one conductor’s resistance per foot, and L is one-way distance. The factor 2 accounts for outgoing and returning paths exactly once.
Using resistance in Ω/1000 ft: Vdrop = 2 × I × R_per_1000ft × L_ft / 1000. R_total = 2 × R_per_length × L is the round-trip resistive-path resistance for this model. The user must not enter a round-trip distance.
Balanced three-phase resistive model: Vdrop = √3 × I × R_per_length × L. Enter line-to-line system voltage when calculating percentage and estimated load voltage. Distance remains one-way.
√3 is a phase relationship factor. √3 × R × L is not labeled total circuit resistance. Schneider Electric’s electrical installation guide (opens in a new tab) gives more general formulas with resistance, reactance and phase angle; this page retains only the resistive term and does not model non-unity power factor or reactance.
One-way distance means from source to load, entered once for either circuit model. A 250 ft run is 76.2 m. Switching ft/m preserves that distance. The single-phase return path is handled by 2; balanced three-phase uses √3 instead.
No routing diagram or installation length allowance is implied. The circuit visual is only a source-to-load schematic.
Resistance is derived from nominal cross-sectional area rather than copied from a proprietary code table. R_per_1000ft = K × 1000 / areaCmil. Resistance model referenced at 20 °C. Copper uses standard annealed 100% IACS copper; aluminum uses EC-H19, 61.0% IACS.
AWG diameter in mils = 5 × 92^((36 − g) / 39); circular-mil area is diameter squared. For 1/0 through 4/0, g is 0 through −3. Larger kcmil sizes specify nominal area directly: 250 kcmil = 250,000 circular mils. Resistance decreases as area increases.
NBS Handbook 100 (opens in a new tab) supplies the AWG progression and annealed-copper constant 10.371 Ω·cmil/ft. NBS Handbook 109 (opens in a new tab) supplies the EC-H19 aluminum constant 17.002 Ω·cmil/ft. These are ideal nominal-area estimates, without strand-lay, coating or actual cable-construction adjustments. Use actual product data when those details matter.
To understand the resistive relationship, review the ideal voltage-current-resistance relationship in a separate ideal model. It does not add AC reactance, ampacity checks, protection-device selection or installation approval to this wire-run estimate.
At equal area and the same reference condition, the selected aluminum basis has higher modeled resistance than the copper basis. The material-comparison mode independently finds each material’s smallest supported size using the same voltage, phase, current, one-way distance and target.
EC-H19 is a specific electrical-conductor aluminum basis; it does not represent every aluminum alloy or modern cable product. Comparison does not infer cost, availability, termination suitability, ampacity or a universally preferred material.
dropPct = Vdrop / systemVoltage × 100. The maximum voltage-drop percentage is a user-selected design target. Convenience targets 2%, 3% and 5% and custom targets are not legal limits or compliance judgments.
Within selected voltage-drop target / Exceeds selected voltage-drop target describes only the modeled raw percentage. Even when 3.004% displays as 3.00%, it exceeds a strict 3% target. Only a floating-point tolerance of 8 × Number.EPSILON × max(1, |dropPct|, |target|) is allowed; no hidden design slack.
Iterate the canonical supported dataset from smallest to largest area and select the first conductor satisfying raw dropPct ≤ selected target, within the stated numerical tolerance. The sequence is 14 AWG, 12 AWG, 10 AWG, 8 AWG, 6 AWG, 4 AWG, 3 AWG, 2 AWG, 1 AWG, 1/0 AWG, 2/0 AWG, 3/0 AWG, 4/0 AWG, 250 kcmil, 300 kcmil, 350 kcmil, 400 kcmil, 500 kcmil, 600 kcmil, 750 kcmil, 1000 kcmil. It is not sorted lexically; larger AWG numbers denote smaller conductors.
No ampacity filter is applied. Unsupported intermediate gauges are never interpolated. The nearby matrix shows up to two smaller and two larger entries, centered on the active conductor where available. Why this size? compares the raw-selected conductor with the next smaller supported conductor.
If the largest supported conductor still exceeds the target: No supported conductor size in this calculator meets the selected voltage-drop target. The diagnostic matrix/formulas use the largest supported entries, without selecting or extrapolating a conductor.
Voltage-drop sizing and ampacity are different questions. A conductor with low enough modeled voltage drop may still be unsuitable for current, terminal ratings, installation method or applicable requirements. No ampacity table or hidden current-to-gauge rule is used here.
This checks voltage drop only. It does not determine whether the conductor has sufficient ampacity or meets installation requirements. Electrical note: This calculator estimates voltage drop only. It does not determine conductor ampacity, breaker/fuse size, terminal temperature rating, installation method, grounding/bonding, conduit requirements, or code compliance.
Enter the conductor size you already selected from your ampacity/code/design process. This calculator can then show whether voltage-drop considerations would move you to a larger supported size.
If the baseline fails the selected target and a supported larger conductor meets it, the engine lists each entry from baseline to result and counts supported dataset steps. AWG numbering is not subtracted numerically. If the baseline already meets the target, it is retained: No voltage-drop upsize needed. There is no downsizing recommendation.
A baseline applies to the selected material only. Material-comparison cards show unconstrained voltage-drop minima; they do not transfer a baseline ampacity selection between copper and aluminum.
estimatedLoadVoltage = systemVoltage − Vdrop. It is labeled Estimated voltage at load. Estimated voltage at load assumes the source remains at the entered nominal voltage; source sag, transformer regulation and upstream conductor drop are not modeled.
If calculated drop equals or exceeds source voltage, the algebraic zero/negative load result is outside a useful operating estimate; actual load behavior is not predicted by this simple model. A no-supported-size result is not extrapolated.
Resistance model referenced at 20 °C using nominal conductor area. Warmer conductors generally have higher resistance. Actual cable construction and operating conditions can change voltage drop.
Actual AC voltage drop can also depend on conductor reactance, power factor, wiring method, frequency, conductor temperature, and installation conditions. This calculator uses the documented resistive model shown in the methodology.
The fixed 20 °C condition is not a conductor temperature rating or an operating-temperature prediction. No temperature selector is provided. There is no power-factor input because reactive impedance is not modeled. Resistance displays use five significant figures; drop, percentage and estimated load voltage normally use two decimals.
240 V; Single-phase; 60 A; 250 ft one-way; Copper; 3% selected target.
3 AWG Copper: 5.91 V drop; 2.46%; estimated load 234.09 V; Within selected voltage-drop target; resistance 0.19704 Ω/1000 ft at 20 °C
240 V; Single-phase; 60 A; 250 ft one-way; Copper; 3% selected target.
6 AWG Copper: 11.85 V drop; 4.94%; estimated load 228.15 V; Exceeds selected voltage-drop target; resistance 0.39507 Ω/1000 ft at 20 °C
480 V; Three-phase; 100 A; 300 ft one-way; Copper; 3% selected target.
4 AWG Copper: 12.91 V drop; 2.69%; estimated load 467.09 V; Within selected voltage-drop target; resistance 0.24846 Ω/1000 ft at 20 °C
240 V; Single-phase; 60 A; 250 ft one-way; Copper; 3% selected target.
3 AWG Copper: 5.91 V drop; 2.46%; estimated load 234.09 V; Within selected voltage-drop target; resistance 0.19704 Ω/1000 ft at 20 °C
User-entered baseline 6 AWG Copper: 11.85 V drop; 4.94%; estimated load 228.15 V; Exceeds selected voltage-drop target; resistance 0.39507 Ω/1000 ft at 20 °C. Upsize path 6 AWG → 4 AWG → 3 AWG (2 supported steps).
240 V; Single-phase; 60 A; 250 ft one-way; Copper; 3% selected target.
3 AWG Copper: 5.91 V drop; 2.46%; estimated load 234.09 V; Within selected voltage-drop target; resistance 0.19704 Ω/1000 ft at 20 °C
3 AWG Copper: 5.91 V drop; 2.46%; estimated load 234.09 V; Within selected voltage-drop target; resistance 0.19704 Ω/1000 ft at 20 °C
1 AWG Aluminum: 6.09 V drop; 2.54%; estimated load 233.91 V; Within selected voltage-drop target; resistance 0.20315 Ω/1000 ft at 20 °C
Nominal-area, straight-conductor resistive model at 20 °C. R per 1000 ft = K × 1000 / area in circular mils; K is 10.371 for standard annealed copper and 17.002 for EC-H19 aluminum, in Ω·cmil/ft. No strand-lay, coating, operating-temperature or AC-impedance corrections.
Only one conductor per modeled current path; no parallel conductors, ampacity, breaker/fuse recommendation, grounding/bonding, terminal rating, conduit, fault, arc-flash, transformer, motor-specific or service design. No safe/approved or code-compliant conductor judgment.
Software bounds: positive inputs at least 0.000001 in normalized units; voltage/current up to 1,000,000 V/A; one-way distance up to 10,000,000 ft; target strictly greater than 0% and less than 100%; derived drop at most 10^15 V. These are software bounds, not code criteria. Strings are capped at 64 characters and enum selectors use supported values. Invalid inputs or missing data clear results, visual, comparison and matrix and disable copy/print.
Electrical note: This calculator estimates voltage drop only. It does not determine conductor ampacity, breaker/fuse size, terminal temperature rating, installation method, grounding/bonding, conduit requirements, or code compliance. Verify applicable electrical requirements, equipment ratings and installation conditions before installation. Calculations are local to this page session, without saved projects or numeric URL persistence.
Multiply load current by conductor resistance over the one-way distance and the circuit factor: 2 for the two-wire single-phase model or √3 for balanced three-phase.
The engine already accounts for the supported current-path or phase relationship. Entering round-trip distance would apply the single-phase return path twice.
Vdrop = 2 × I × R_per_length × L using one-way length and resistance at the documented reference condition.
Use √3 × I × R_per_length × one-way length for the balanced resistive approximation. Enter line-to-line source voltage for percentage and load-voltage estimates.
Larger nominal area reduces modeled resistance and drop at the same current and distance. Selection uses the supported ordered dataset, not interpolated gauges.
The documented copper and EC-H19 aluminum resistivity constants differ. Other alloys and actual cable products can have different resistance.
It is your selected design target compared with raw modeled drop/system voltage × 100. Target presets are not code limits.
A conductor selected through a separate ampacity/design process may exceed the desired voltage-drop target on a long run. Enter it as a baseline to see a supported upsize path; the calculator never recommends downsizing.
No. Find and check modes evaluate voltage drop only, without ampacity filtering, breaker/fuse matching or installation design.
No. It only meets your selected target under this resistive model. Applicable electrical requirements, equipment ratings and installation conditions still require verification.
Reviewed October 4, 2026. Historical public U.S. government handbooks supply nominal dimensions and material constants; calculated resistance rows are derived, not a copied proprietary standards table. Schneider Electric supports the general circuit relationships, while this calculator uses its separately documented 20 °C resistance-only method. NIST supplies exact length conversions. No source endorses BuzCalculator.