Voltage Drop Calculator
Solves for the conductor size needed to hold voltage drop under a target percentage, using the K-constant method (12.9 for copper, 21.2 for aluminum) and circular-mil conductor areas.
What it calculates
- Actual voltage drop for a given conductor size, length and load current
- The smallest standard conductor size that meets a target voltage-drop percentage
- Single-phase and three-phase circuits
Typical inputs
- Load current
- One-way circuit length
- Source voltage
- Conductor material
- Target voltage-drop percentage (commonly 3% branch / 5% total)
Frequently asked
Is the 3%/5% voltage drop limit a hard NEC requirement?
No — it's an Informational Note in 210.19(A) and 215.2(A)(3), meaning it's recommended practice for efficient operation, not an enforceable code violation if exceeded. Most engineers hold to it anyway because equipment often has its own voltage-tolerance requirements.
Autodesk and Revit are registered trademarks of Autodesk, Inc. SYMATEQ is not affiliated with, endorsed by, or sponsored by Autodesk, Inc. SYMATEQ Electrical Calculators is an independent add-in for Autodesk® Revit®. Calculations are engineering aids and do not replace review by a licensed professional engineer or confirmation with the authority having jurisdiction.