Voltage Drop Calculator
Calculate an idealized circuit voltage drop using conductor resistance and the complete current path. The result separates calculated performance from conductor ampacity and code-compliance decisions.
How to use the Voltage Drop Calculator
Enter copper or aluminum, DC or AC phase type, AWG conductor size, one-way length, load current, and source voltage.
Review actual conductor resistance, termination temperature, phase configuration, power factor, ampacity, continuous-load rules, and adopted electrical code.
Read nominal conductor area, assumed resistance, voltage drop, percentage drop, and estimated load voltage.
Formula
Using nominal circular-mil area and material constant K, DC or single-phase drop ΔV = 2KLI ÷ CM; three-phase drop ΔV = √3KLI ÷ CM. Percentage drop = ΔV ÷ source voltage × 100.
Example
A 120 V circuit with a calculated 3.0 V loss delivers about 117 V and has 2.5% voltage drop.
Assumptions and limitations
- The estimate excludes reactance, temperature, ampacity, overcurrent protection, grounding, and code compliance; hazardous electrical work requires qualified review.
- Voltage Drop Calculator treats the entered values as estimates and does not infer missing project, account, or personal details.
- Calculations retain working precision except where the cited method requires an intermediate rounding step; displayed values are then formatted separately. Source rules and dated rates must be rechecked when they change.
Sources
- National Fire Protection Association: NFPA 70, National Electrical CodeElectrical-system design and voltage-drop informational guidance. Reviewed 2026-08-14.
- National Institute of Standards and Technology: SI Units — Electric CurrentSI electrical units and definitions. Reviewed 2026-08-14.
- ASTM International: ASTM B258 — Standard Nominal Diameters and Cross-Sectional Areas of AWG SizesOfficial formula, rate, or program guidance used by this calculator. Reviewed 2026-08-14.
- National Fire Protection Association: NFPA 70, National Electrical Code, 2023 editionOfficial formula, rate, or program guidance used by this calculator. Reviewed 2026-08-14.
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Frequently asked questions
How does the Voltage Drop Calculator work?
Using nominal circular-mil area and material constant K, DC or single-phase drop ΔV = 2KLI ÷ CM; three-phase drop ΔV = √3KLI ÷ CM. Percentage drop = ΔV ÷ source voltage × 100.
What information should I enter in the Voltage Drop Calculator?
Enter copper or aluminum, DC or AC phase type, AWG conductor size, one-way length, load current, and source voltage, then verify actual conductor resistance, termination temperature, phase configuration, power factor, ampacity, continuous-load rules, and adopted electrical code.
What should I verify before using this Voltage Drop Calculator result?
The estimate excludes reactance, temperature, ampacity, overcurrent protection, grounding, and code compliance; hazardous electrical work requires qualified review.
Reviewed 2026-08-14 · 1.0.0 · content-2026-08-14 · Trusty Calculator Editorial Team