Voltage Drop Calculator — Wire Size, Distance & Drop
Plan branch circuits and feeders with residential or commercial temperature modes. Switch between minimum conductor size, maximum run length, and voltage-drop results — all in your browser.
System parameters
Homeowner-oriented: single-phase, 60 °C ampacity, no parallels, max 100 A.
Locked to single in residential mode.
Input parameters
How to use this voltage drop calculator tool
- Choose residential or commercial temperature mode (60 °C, 75 °C, or 90 °C ampacity basis).
- Set power factor, AC or DC, length units, phase, conductor material, and installation type.
- Pick a calculator mode: minimum conductor size, maximum circuit distance, or voltage drop for a known size and length.
- Enter voltage, load amps, max allowed drop %, length (when required), conductor size (when required), and parallel sets.
- Review drop in volts and percent, ampacity check, recommended size or max distance, and the calculation steps.
About this voltage drop calculator tool
Excessive voltage drop causes motors to overheat, lights to dim, and sensitive electronics to misbehave. Rankify's voltage drop calculator helps you estimate conductor size and run length so the voltage at the load stays within your design target — commonly about 3% on branch circuits and 5% feeder-plus-branch combined for many installations.
Use minimum conductor size when you know the load, voltage, allowed drop, and one-way length. Use maximum circuit distance when the wire size is already chosen and you need the longest run that still meets the drop limit. Use voltage drop mode when both size and length are known and you only need the resulting volts and percent.
Residential mode keeps the workflow simple: single-phase, 60 °C ampacity basis, no parallels, and circuits at or under 100 A. Commercial modes unlock three-phase, parallels, and 60 / 75 / 90 °C ampacity columns for professional planning.
Voltage Drop Calculator — Options & Inputs
- System modes: residential (conservative single-phase) or commercial 60 / 75 / 90 °C
- Calculator modes: minimum conductor size, maximum circuit distance, voltage drop
- Power factor 0–1 for AC impedance-style estimates
- AC or DC current; feet or meters for cable length
- Single-phase or three-phase; copper or aluminum
- Installation: nonmagnetic conduit / cable / burial vs steel conduit (reactance)
- Conductor sizes from 14 AWG through 1000 kcmil; parallel conductor sets
What You Get
Each run returns the same structured results — values change with your inputs.
- Voltage drop in volts and as a percent of system voltage
- Estimated voltage at the load
- Minimum recommended conductor size (size mode)
- Maximum one-way circuit distance (distance mode)
- Approximate ampacity check against the selected temperature column
- Step-by-step notes explaining the estimate
How voltage drop is estimated
For DC and near-unity power factor AC, the tool uses the classic circular-mil formula with copper and aluminum constants and a single-phase or three-phase multiplier. Parallel sets divide the effective current per conductor.
When AC power factor is below 1, the estimate uses approximate conductor resistance and raceway reactance so inductive drop is included. Steel conduit uses a higher reactance table than PVC, cable tray, or direct burial style nonmagnetic paths.
These formulas are widely taught for preliminary sizing. Final designs should still apply ambient corrections, continuous-load factors, and the exact tables in the electrical code adopted in your jurisdiction.
Choosing max voltage drop percent
Many designers target about 3% drop on a branch circuit and keep feeder plus branch under about 5% so utilization equipment still sees adequate voltage. Critical loads, long motor feeders, and LED lighting sometimes need tighter budgets.
Raising the allowed percent shortens required wire size but increases heat and performance risk. If the calculator cannot find a size that meets both ampacity and drop, shorten the run, increase parallels, or raise voltage class where allowed.
Copper vs aluminum and parallels
Copper has lower resistivity, so the same ampacity often needs a smaller copper size than aluminum for the same drop. Aluminum feeders are common for cost and weight; ensure terminations and connectors are rated for aluminum.
Parallel conductors (joined at both ends) share current and reduce drop. Residential mode disables parallels for simplicity; commercial modes allow multiple sets when your design uses them.
From wire size to conduit fill
After you settle on AWG or kcmil, open the conduit fill calculator to check raceway percentage and jam risk for THHN, XHHW, and related insulation types. Sizing the conductor and the conduit together avoids redesign when the pull is already scheduled.
Important Notes & Limitations
- Ampacity and reactance values are planning approximations — not a substitute for the full code tables, adjustment factors, or engineered designs.
- Residential mode intentionally limits phase, parallels, and current for a simpler homeowner-oriented workflow.
- Long runs, harmonics, high ambient temperature, and bundling may require larger conductors than this tool suggests.
- Always have a qualified electrician or electrical engineer confirm final wire sizing for permits and safety.
Why use Rankify for voltage drop calculator?
- Three calculator modes in one place — size, distance, and drop — without leaving Rankify.
- Residential and commercial temperature modes so you can match the workflow you need.
- Copper and aluminum, AC/DC, feet/meters, and parallel sets for real feeder planning.
- Pairs with the conduit fill calculator when you move from conductor size to raceway fill.
- Runs entirely in the browser — no signup and no upload of project files.
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voltage drop calculator — frequently asked questions
Frequently Asked Questions
Yes. Rankify offers this voltage drop calculator at no cost with no account required. Calculations run in your browser.
A common planning target is about 3% on the branch circuit and about 5% for feeder plus branch combined. Your project specs or local rules may require tighter limits for motors or sensitive equipment.
Yes. Residential mode is single-phase only, uses a 60 °C ampacity basis, disallows parallels, and caps load at 100 A for a conservative homeowner-oriented workflow. Commercial modes allow three-phase, parallels, and 60 / 75 / 90 °C columns.
Yes in commercial modes. Select three-phase; the estimate uses the √3 multiplier with AC resistance and reactance when power factor is below 1.
No. The tool provides planning estimates. Verify ampacity adjustments, temperature ratings, termination limits, and adopted code requirements with a qualified professional before purchasing or installing conductors.