Free Voltage Drop Calculator - Electrical Made Easy
Calculate voltage drop in electrical circuits based on wire length, gauge, and current. Ensure safe, efficient electrical installations within code limits.
Quick Answer
NEC recommends max 3% voltage drop on branch circuits. On 120V circuit, that is 3.6V. Use larger wire gauge or shorter runs to reduce drop.
Key Facts about Voltage Drop Calculator:
- Max recommended: 3% branch, 5% total
- VD = 2 × current × resistance × length
- Larger wire = less voltage drop
- Copper has lower resistance than aluminum
- 3% of 120V = 3.6V maximum drop
Why Use Our Voltage Drop Calculator?
Complete voltage calculations:
Voltage Drop
Calculate wire losses.
Wire Sizing
Find correct gauge.
Code Compliance
NEC recommendations.
Both Materials
Copper and aluminum.
Instant Results
Get drop immediately.
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How to Voltage Drop Calculator in 3 Easy Steps
Calculate voltage drop:
Enter Values
Current, length, gauge.
Select Material
Copper or aluminum.
Get Drop
See voltage drop and %.
Safe Electrical
Code-compliant wiring
Proper wire sizing
Efficient installations
Safety assurance
Common Use Cases for Voltage Drop Calculator
Perfect for:
Frequently Asked Questions
Everything you need to know about our voltage drop calculator
What is acceptable voltage drop?
3% for branches, 5% total (NEC recommendation)
NEC recommends max 3% for branch circuits, 5% total (feeder + branch). On 120V: 3% = 3.6V drop, 5% = 6V drop. Lower is better for efficiency.
How do I calculate voltage drop?
VD = (2 × K × I × Distance) / Circular Mils
VD = (2 × K × I × D) / CM. K=resistivity (copper≈12.9), I=current(amps), D=distance(feet), CM=wire circular mils. Or use: VD = 2 × I × R × length.
How does wire gauge affect voltage drop?
Larger wire (smaller gauge number) = less voltage drop
Larger gauge (smaller number) = less resistance = less voltage drop. Going from 14 AWG to 12 AWG reduces resistance by ~37%. For long runs, upsize the wire.
Still have questions? Try the tool yourself!
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