When to use it
Use it for early sizing and scenario comparisons on two-conductor DC or single-phase runs. Ampacity, insulation rating, temperature, bundling, terminations, protection, and applicable code must still be checked separately.
Voltage Drop Calculator
Estimate DC/single-phase voltage drop for copper or aluminum.
Everything runs in your browserNo account requiredPrivacy-firstv1.0.0Updated Aug 5, 2026
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Circuit parameters
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Conductor material
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About the voltage drop calculator
Estimate conductor voltage drop for a DC or single-phase circuit using the approximate-resistance formula VD = 2 · K · I · L / CM.
How it works
Load current, one-way run length, wire AWG size, and conductor material feed into the classic K-factor method. The factor of 2 accounts for the out-and-back conductor path. Source voltage is used only to express drop as a percentage.
Wire sizes
AWG sizes come from the built-in reference table (4/0 through 40 AWG). Reference ampacity values shown in the dropdown are typical NEC Table 310.16-style figures for copper — not a code determination on their own.
Limitations
This is a simplified DC-resistance approximation. It ignores conductor temperature rise, AC skin and proximity effects, and reactance. Three-phase circuits use a different multiplier (√3, not 2) and are out of scope. It is not a substitute for an NEC Chapter 9 voltage-drop study or a licensed electrician's calculation.
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All calculations run locally in your browser. Nothing you type is sent to a Dockzio server.
Practical guidance
Use voltage drop as one check in conductor selection
The calculator estimates resistive drop for DC or simple single-phase circuits. It helps compare run length, current, conductor material, and AWG size, but it does not perform a complete electrical design.
Worked example
For a 120 V, 15 A copper circuit with a 50 ft one-way run and 12 AWG conductor, the K-factor estimate is about 2.4 V drop, or roughly 2.0%. Doubling the one-way length approximately doubles the drop when the other inputs stay fixed.
Formula and inputs
The approximation is VD = 2 × K × I × L ÷ CM. K represents conductor resistivity, I is current, L is one-way length, and CM is circular-mil area. Percent drop is VD ÷ source voltage × 100. The factor 2 represents outbound and return paths.
Limits and safety
The simplified model omits temperature-adjusted resistance, AC reactance, harmonics, power factor, connection losses, and three-phase geometry. Do not use it as an ampacity ruling, code determination, or substitute for a licensed electrical professional.
FAQ
Quick answers to common questions.
Yes. Voltage Drop Calculator is free to use with no account required.
No. This tool runs entirely in your browser. Nothing you enter is sent to a Dockzio server.
Learning Center
Guides related to Voltage Drop Calculator
Short explainers that pair well with this tool — concepts first, then practice.
- Voltage Drop: Keeping Circuits Within Spec8 min read→
- Wire Gauge Explained: AWG, Ampacity, and Choice7 min read→