Wire Gauge Calculator
Estimate AWG wire size for any run and load.
Use this wire gauge calculator to estimate the required AWG wire size for any run and load. The calculation uses amperage, one-way distance, conductor material, and allowable voltage drop, then identifies the smallest AWG wire with at least the required circular mil area.
Minimum wire
#8
copper AWG
Circular mils
14,333
CM required
Max drop
3.6
volts
Save this project
Sign in to save calculations to your dashboard.
Download your PDF report & project guide
Your results and inputs, a printable shopping list, a step-by-step guide and pro tips — in one PDF.
Planning a whole project?
Get every calculator, a full shopping list and a budget template for:
Recommended tools & materials
Handy picks for this project on Amazon.
Wire Stripper
Clean strips for 10–20 AWG
View on Amazon →
Digital Multimeter
Test voltage and continuity safely
View on Amazon →
Non-Contact Voltage Tester
Check for live wires first
View on Amazon →
Wire Connector Assortment
Twist-on and lever nuts
View on Amazon →
As an Amazon Associate, MaterialCalc earns from qualifying purchases.
How does the wire gauge calculator work?
Circular mils = (2 × K × amps × one-way distance) ÷ allowable voltage drop, where K = 12.9 for copper. Then pick the smallest AWG with at least that many CM.
What else do people ask about this calculator?
What wire size for a 20 amp circuit?
12 AWG copper up to ~50 ft on 120 V; for longer runs step up to 10 AWG to keep voltage drop under 3%.
Why does distance matter?
Longer runs multiply resistance, dropping voltage. NEC recommends keeping branch-circuit drop under 3%.
Which related calculators should I use next?
All calculators
Complete Your Wiring Project
These practical tools and connectors help you work safely and complete residential wiring projects.
Klein Voltage Tester
Search on Amazon →
WAGO 3-Wire Connectors
Search on Amazon →
Southwire 12/2 Cable
Search on Amazon →
Paid links: as an Amazon Associate, MaterialCalc earns from qualifying purchases.